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Deploy Alternative Refrigerants

Highly Recommended
Supermarket refrigerator

This solution involves reducing the use of high-global warming potential (GWP) refrigerants, instead deploying lower-GWP refrigerants. High-GWP (>800 on a 100-yr basis) fluorinated gases (F-gases) are currently used as refrigerants in refrigeration, air conditioning, and heat pump systems. Over the lifetime of this equipment, refrigerants escape into the atmosphere where they contribute to climate change. 

Leaked lower-GWP refrigerant gases trap less heat in the atmosphere than do higher-GWP gases, so using lower-GWP gases reduces the climate impact of refrigerant use. In our analysis, this solution is only deployed as new equipment replaces decommissioned equipment because alternative refrigerants cannot typically be retrofitted into existing systems.

Last updated November 5, 2025

Solution Basics

kt high-GWP refrigerant phased out

t CO₂-eq (100-yr)/unit
units
Current 440 05,5005,900
Achievable (Low to High)

Climate Impact

Gt CO₂-eq (100-yr)/yr
Current 0.2 2.52.7
US$ per t CO₂-eq
50
Emergency Brake

F-gases

Additional Benefits

183
    183
    • 184
    • 185
    • 186
    • 187
    • 188
191,194

Overview

Refrigerants are chemicals that can absorb and release heat as they move between gaseous and liquid states under changing pressure. In this solution, we considered their use in six applications: residential, commercial, industrial, and transport refrigeration as well as stationary and mobile air conditioning. Heat pumps double as heating sources, though they are included here with air conditioning appliances. Refrigerants are released to the atmosphere during manufacturing, transport, installation, operation, repair, and disposal of refrigerants and equipment. Deploy Alternative Insulation Materials covers the use of refrigerant chemicals to produce foams.

Climate impacts of emissions of refrigerants can be reduced by:

  • using lower-GWP refrigerants
  • reducing leaks during equipment manufacturing, transport, installation, use, and maintenance
  • reclaiming refrigerant at end-of-life and destroying or recycling it
  • using less refrigerant through efficiency improvements or reduction in demand.

This solution evaluated the use of lower-GWP refrigerants alone. Leak reduction and responsible disposal are covered in Improve Refrigerant Management. Lowering use of and demand for refrigerants – while outside the scope of these assessments – is the most effective way to reduce emissions.

Most refrigerants used in new equipment today are a group of F-gases called hydrofluorocarbons (HFCs) (Figure 1). HFCs are GHGs and are typically hundreds to thousands of times more potent than CO₂  (Smith et al., 2021). Since high-GWP refrigerants are usually short-lived climate pollutants, their negative climate impacts tend to be concentrated in the near term (Shah et al., 2015). High-GWP HFC production and consumption are being phased down under the Kigali Amendment to the Montreal Protocol, but existing stock and production remains high worldwide (Amendment to the Montreal Protocol on Substances That Deplete the Ozone Layer, 2016; United Nations Framework Convention on Climate Change [UNFCCC], 2023). Other types of refrigerants that deplete the ozone layer – including chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) — are also being phased out of new production and use globally (Montreal Protocol on Substances That Deplete the Ozone Layer, 1987; Figure 1).

Figure 1. Examples of common refrigerants and their climate and environmental impacts

High-GWP: red; Medium-GWP: yellow; Low-GWP: green

Type GWP
(20-yr)		 GWP
(100-yr)		 Life
(yr)		 Ozone
Depleting?		 PFAS? Safety
Class*
R11CFC8,3206,23052YesA1
R12CFC12,70012,500102YesA1
R22HCFC5,6901,96011.9YesA1
R141bHCFC2,7108609.4Yes
R125HFC6,7403,74030NoYesA1
R134aHFC4,1401,53014NoYesA1
R143aHFC7,8405,81051NoYesA2L
R404AHFC
blend		7,2084,728NoYesA1
R407CHFC
blend		4,4571,908NoYesA1
R410AHFC
blend		4,7152,256NoYesA1
R452AHFC/HFO
blend		4,2732,292NoYesA1
R32HFC2,6907715.4NoNoA2L
R452BHFC/HFO
blend		2,275779NoYesA2L
R454AHFC/HFO
blend		943270NoYesA2L
R513AHFC/HFO
blend		1,823673NoYesA1
R290
(Propane)		Natural0.0720.020.036NoNoA3
R600a
(Isobutane)		Natural< 1< 10.019NoNoA3
R717
(Ammonia)		Natural< 1< 1< 1NoNoB2L
R744
(CO₂)		Natural11NoNoA1
R1234yfHFO1.810.5010.033NoYesA2L
R1234ze(E)HFO4.941.370.052NoYesA2L

*Safety classes based on ASHRAE Standard 34: 

A1: non-flammable, lower toxicity

A2L: lower flammability, lower toxicity

A3: higher flammability, lower toxicity

B2L: lower flammability, higher toxicity

 

Sources:

Baha, M., & Dupont, J.-L. (2023, September 15). Global warming potential (GWP) of HFC refrigerants. International Institute of Refrigeration. 

Behringer, D., Heydel, F., Gschrey, B., Osterheld, S., Schwarz, W., Warncke, K., Freeling, F., Nödler, K., Henne, S., Reimann, S., Blepp, M., Jörß, W., Liu, R., Ludig, S., Rüdenauer, I., & Gartiser, S. (2021). Persistent degradation products of halogenated refrigerants and blowing agents in the environment: Type, environmental concentrations, and fate with particular regard to new halogenated substitutes with low global warming potential. Final report. Umweltbundesamt [German Environment Agency]. 

Burkholder, J. B., Hodnebrog, Ø., McDonald, B. C., Orkin, V., Papadimitriou, V. C., & Van Hoomissen, D. (2023). Annex: Summary of abundances, lifetimes, ODPs, REs, GWPs, and GTPs. Scientific Assessment of Ozone Depletion 2022. 

Garry, M. (2021, June 23). Certain HFCs and HFOs are in PFAS group that five EU countries intend to restrict. 

Smith, C., Nicholls, Z. R. J., Armour, K., Collins, W., Forster, P., Meinshausen, M., Palmer, M. D., & Watanabe, M. (2021). The Earth’s energy budget, climate feedbacks, and climate sensitivity supplementary material. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. 

Trevisan, T. (2023, July 3). Overview of PFAS refrigerants used in HVAC&R and relevance of refrigerants in the PFAS Restriction Intention. UN Montreal Protocol 45th OEWG, Bangkok. 

United Nations Environment Programme. (2023). Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee: 2022 assessment report. 

United Nations Environment Programme & ASHRAE. (2025). Update on new refrigerants designations and safety classifications June 2025. 

In this solution, production and consumption of high-GWP refrigerants (which we defined as GWP>800, 100-yr basis) are avoided by the use of lower-GWP refrigerants in new equipment. These alternative refrigerants can still leak to the atmosphere, but their heat-trapping effect is much lower. Some promising alternatives have low GWPs (<5, 100-yr basis), including some hydrofluoroolefins (HFOs) as well as natural refrigerants, which include CO₂, ammonia, propane, and isobutane. (Figure 1). However, the adoption of these low-GWP refrigerants comes with challenges, including flammability, cost, building codes, and technical limitations (see Risks and Take Action sections below).

Refrigerants with medium GWPs (<800, 100-yr basis; <2,700, 20-yr basis (Smith et al., 2021)) can also be near-term alternatives that increase adoption while providing a climate benefit. In our analysis, we separately considered medium-GWP alternatives in applications where low-GWP alternatives are less common (Figure 2).

Figure 2. Alternative refrigerants used to calculate the low-GWP and medium-GWP scenarios. The low-GWP scenario assumed equipment using high-GWP refrigerants is replaced at end-of-life with equipment using alternative refrigerants with GWP<5. The medium-GWP calculations assumed GWP<800 (100-yr basis) and GWP<2,700 (20-yr basis) alternatives in applications where low-GWP replacements are currently less common (commercial refrigeration, transport refrigeration, stationary air conditioning) and assumed low-GWP replacements for the remaining applications where they are more developed technologies (residential refrigeration, industrial refrigeration, mobile air conditioning). The alternative refrigerants in the table are used for effectiveness and/or cost calculations. 

Application Scenario 1: Low-GWP only
(low GWP: < 5, 100-year basis) 		Scenario 2: Medium-GWP when low-GWP alternatives are less common, otherwise low-GWP
(medium GWP: < 800, 100-year basis)
Residential refrigeration Isobutane
Commercial refrigeration Propane, CO₂ Medium-GWP HFC and HFO blends
Industrial refrigeration Ammonia, CO₂, propane
Transport refrigeration Propane, propene, ammonia, CO₂,
low-GWP HFOs		 Medium-GWP HFC and HFO blends
Mobile air conditioning CO₂, low-GWP HFOs
Stationary air conditioning Propane, CO₂,
ammonia, low-GWP HFOs		 Medium-GWP HFC and HFO blends

Sources:

Purohit, P., & Höglund-Isaksson, L. (2017). Global emissions of fluorinated greenhouse gases 2005–2050 with abatement potentials and costs. Atmospheric Chemistry and Physics, 17(4), 2795–2816. 

Sustainable Purchasing Leadership Council Climate Friendly Refrigerant Action Team. (2021). Recommendations for climate friendly refrigerant management and procurement. 

United Nations Environment Programme. (2023). Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee: 2022 assessment report. 

United Nations Framework Convention on Climate Change. (2023). National inventory submissions, Annex 1 parties [Data set]. 

U.S. Environmental Protection Agency. (2011). Transitioning to low-GWP alternatives in transport refrigeration. 

There is currently no single refrigerant that perfectly fits the climate, safety, and performance requirements for all applications. Instead, the optimal alternative refrigerant will vary depending on equipment type and location (United Nations Environment Programme [UNEP], 2023). 

Generating electricity to run heating, ventilation, air conditioning, and refrigeration (HVAC&R) equipment also produces high levels of emissions (mostly CO₂ ) at power plants – more than twice the emissions from direct release of refrigerants (United Nations Development Programme [UNDP], 2022). Using alternative refrigerants can impact efficiency, changing these electricity-related emissions. However, indirect emissions are not quantified in this solution.

Impact Calculator

Adjust effectiveness and adoption using range sliders to see resulting climate impact potential.

Effectiveness

t CO2-eq/kt high-GWP refrigerant phased out/yr
25th
percentile
400,000
75th
percentile
460,000
median

Adoption

440
kt high-GWP refrigerant phased out
Low
5,500
High
5,900
440
current
Achievable Range

Climate Impact

0.00
Gt CO₂-eq/yr (100-yr)
05
which is the equivalent of
0.00%
of global emissions

The Details

Current State

For every kt high-GWP refrigerant phased out in favor of low-GWP refrigerant, approximately 460,000 t CO₂‑eq/yr of F-gas emissions will be mitigated on a 100-yr basis (Table 1). If medium-GWP refrigerants are instead adopted in certain applications (Figure 2), the effectiveness decreases to 400,000 t CO₂‑eq (100-yr)/kt high-GWP refrigerant phased out/yr (Table 1). Effectiveness is based on average GWP of the high-, low-, and medium-GWP refrigerants; the difference in refrigerant charge; and the expected percent released to the atmosphere.

Since F-gases are short-lived climate pollutants, the effectiveness of this solution on a 20-yr basis is higher than on a 100-yr basis. Switching to low-GWP refrigerants saves 860,000 t CO₂‑eq /kt high-GWP refrigerant phased out/yr on a 20-yr basis. Medium-GWP refrigerants in certain applications reduces the effectiveness to 700,000 t CO₂‑eq (20-yr)/kt high-GWP refrigerant phased out/yr.

Using low-GWP refrigerants mitigates almost all CO₂‑eq emissions from direct release of high-GWP refrigerants. Medium-GWP refrigerants potentially offer a faster path to adoption in certain applications, but yield a smaller reduction in CO₂‑eq emissions. Switching to the lowest possible GWP refrigerant appropriate for a given application will have the highest effectiveness at cutting emissions.

Table 1. Effectiveness at reducing emissions using low-GWP refrigerants only or medium-GWP refrigerants in some applications and low-GWP alternatives otherwise

Unit: t CO₂‑eq /kt high-GWP refrigerant phased out/yr, 100-yr basis

Average – Low GWP only 460000
Average – Medium & low GWP 400000

We estimated the cost of purchasing and using low-GWP alternative refrigerants and equipment by taking a weighted average across all application types, averaging to US$23 million/kt high-GWP refrigerant phased out/yr. A kt of refrigerant goes a long way; a typical residential air conditioner requires only 0.6–3 kg refrigerant, depending on the country and refrigerant type (CLASP & ATMOsphere, 2022). On average across all applications, the emissions abatement cost for this solution is only US$50/t CO₂‑eq on a 100-yr basis (Table 2), or US$27/t CO₂‑eq on a 20-yr basis.

We separately evaluated the net costs of using medium-GWP refrigerants in some applications (Figure 2). Using medium-GWP refrigerants brought average costs down to US$9.4 million/kt high-GWP refrigerant phased out/yr. The emissions abatement cost is US$24/t CO₂‑eq (100-yr basis) or US$13/t CO₂‑eq (20-yr basis).

We calculated cost using values of initial cost and annual operation and maintenance costs from Purohit and Höglund-Isaksson (2017). The overall net cost is a weighted average of the average net costs of switching to alternative refrigerants for each of the six refrigerant applications (Figure 2). Costs are likely to change as the HFC phase-down continues under the Kigali Amendment. We did not evaluate external costs such as those to manufacturers. 

Although our calculated costs are averages, costs varied widely depending on the specific equipment, refrigerant type, and geographic location. Using ammonia in industrial refrigeration yields net savings of US$24 million/kt high-GWP refrigerant/yr. Low-GWP alternative refrigerants for transport refrigeration lead to cost savings over high- or medium-GWP refrigerants, as do hydrocarbons in residential and commercial air conditioning.

We did not consider energy cost differences due to changes in efficiency. Since electricity costs are the majority of the life-cycle costs for certain equipment, these changes in energy costs may be significant (Goetzler et al., 2016).

Table 2. Cost per unit of climate impact for low-GWP refrigerants.

Unit: 2023 US$/t CO₂‑eq , 100-yr basis

Average 50.00

We did not find a learning rate for this solution, although there is evidence that costs of equipment and refrigerant decrease as more alternative refrigerants are deployed. Zanchi et al. (2019) claim that after regulations limiting emissions from F-gases and capping allowable refrigerant GWP were enacted in Europe, component prices for natural refrigerant equipment – particularly in commercial refrigeration – became comparable with lower HFC unit prices. Equipment prices have trended downwards through other similar technological transitions in the past (JMS Consulting & Inforum, 2018).

The cost of refrigerants can change with adoption as well as the cost of equipment. Natural refrigerants tend to be inexpensive, but cost premiums for expensive HFO refrigerants could drop by more than 75% as production volumes increase (Booten et al., 2020). Certain expensive-to-produce alternative refrigerants like HFO-1234yf have limited information about possible future price reductions, but other refrigerant transitions have indicated that prices should decrease due to increased production experience, capacity, and number of producers – especially as patents expire (Sherry et al., 2017). 

Speed of action refers to how quickly a climate solution physically affects the atmosphere after it is deployed. This is different from speed of deployment, which is the pace at which solutions are adopted.

At Project Drawdown, we define the speed of action for each climate solution as emergency brake, gradual, or delayed.

Deploy Alternative Refrigerants is an EMERGENCY BRAKE climate solution. It has the potential to deliver a more rapid impact than gradual and delayed solutions. Because emergency brake solutions can deliver their climate benefits quickly, they can help accelerate our efforts to address dangerous levels of climate change. For this reason, they are a high priority.

Adoption

We estimated that 440 kt high-GWP refrigerants already have been phased out in favor of low-GWP alternative refrigerants worldwide (Table 3). For adoption, we did not differentiate between low- and medium-GWP alternative refrigerants due to insufficient data. 

There are limited recent and global data available to quantify the adoption of alternative refrigerants. For this reason, our approach to quantifying adoption is a simplified approximation. We used projected 2022 HFC emissions from Velders et al. (2015) as our baseline. These projections were made before any Kigali Amendment phase-down began, and we assumed they represent a reasonable 2022 emissions picture in the absence of policy-regulated HFC reductions. 

To calculate current adoption, we analyzed a Velders et al. (2022) model of 2022 HFC emissions accounting for current policies. Projected 2022 emissions in the current model were 6.4% lower than the 2015-projected baseline, which we assumed to be proportional to the amount of high-GWP HFC phased out and replaced with low-GWP alternatives. We estimated current adoption by applying this assumption to an estimated 6,480 kt bank of existing refrigerants (Climate and Ozone Protection Alliance, 2025). That bank includes all HFC and ozone-depleting refrigerants in new, in-use, and end-of-life equipment, and represents the potential refrigerant that could be replaced by alternative refrigerants. Since some alternative refrigerants were adopted before our 2015 baseline, the current adoption value is likely an underestimate.

Some applications are known to have higher levels of current adoption than others. For example, 800 million domestic refrigerators are estimated to use isobutane refrigerant globally, and most of the market for commercial supermarket plug-in cases in Europe, the United States, and Japan use hydrocarbons such as propane (Hayes et al., 2023; UNEP, 2023).

Table 3. Current (2022 modeled) adoption level of low-GWP alternative refrigerants relative to 2015 baseline levels.

Unit: kt high-GWP refrigerant phased out

Estimate 440

We estimated that 77 kt high-GWP refrigerants are phased out for alternative low-GWP refrigerants each year (Table 4). Using the same method as current adoption, we compared baseline and policy-adjusted projections of HFC emissions from Velders et al. (2015, 2022) for 2019–2022. The difference between the projections increased by a median 1.2% year-over-year.

We applied this percent change directly to the 2022 HFC refrigerant bank estimate to determine the tonnage of high-GWP refrigerant that will be phased out as new equipment replaces decommissioned stock. We assumed the replacements all use low-GWP refrigerants.

Although more HFC is being phased out each year, the bank and associated emissions of HFCs are also growing as refrigeration and cooling equipment are more heavily used globally. Alternative refrigerant adoption will need to outpace market growth before net emissions reductions occur. The adoption trend is likely higher today than what is reflected by the data used in our calculations (prior to 2023), since 2024 was a Kigali-mandated increase in HFC phase-down for certain countries. We expect adoption trend to continue to increase as HFC restrictions tighten further in the future.

Table 4. 2019–2022 adoption trend of low-GWP alternative refrigerants.

Unit: kt high-GWP refrigerant phased out/yr

Estimate 77

The adoption ceiling for this solution is phasing out all high-GWP refrigerants, or 6,900 kt globally (Table 5). This value represents the entire current bank of HFCs and ozone-depleting refrigerants added to the current adoption of low-GWP refrigerants (Climate and Ozone Protection Alliance, 2025).

This quantity assumes no increase in the total refrigerant bank above 2022 levels, while in reality the bank is projected to increase substantially as demand for cooling and refrigeration grows worldwide (International Energy Agency [IEA], 2023). Consumption of refrigerants in stationary air conditioning applications alone is projected to increase 3.5-fold between 2020–2050 (Denzinger, 2023). Additionally, new equipment that uses refrigerants (such as heat pump water heaters) is expected to replace non-refrigerant equipment, adding to future refrigerant demand. However, projecting future refrigerant demand was not part of this assessment.

We assumed that in all future cases, high-GWP refrigerants can be phased out for low-GWP alternatives. While ambitious, this ceiling is possible across all applications as new refrigerants, blends, and equipment are developed and commercialized. Since we considered implementation in new equipment, it comes with an adoption delay as existing equipment with high-GWP refrigerants finish their lifespans, which can last 10–20 years (California Public Utilities Commission, 2022; CLASP & ATMOsphere, 2022). 

Table 5. Adoption ceiling for low-GWP refrigerants.

Unit: kt high-GWP refrigerant phased out

Estimate 6,900

The achievable adoption range is clearly laid out by the Kigali Amendment schedule for reduction in HFC consumption and production. The Achievable – Low adoption assumes that worldwide, all countries meet the Kigali phase-down schedule and collectively reach 80% reduction from baseline emissions by 2045. Under the Kigali Amendment, all participating countries are expected to meet at least this standard by this date. It is achievable that this adoption level could be reached collectively across all nations (including higher-adopting countries and non-Kigali signatories). This comes to 5,500 kt reduction in high-GWP refrigerants, calculated as 80% of the sum of net bank and current adoption (Table 6). 

Achievable – High assumes that all countries average the highest Kigali-mandated HFC reduction levels for any country (85% reduction from baseline), which comes to 5,900 kt high-GWP refrigerant phased out when applied to our adoption ceiling. If countries continue to follow the Kigali Amendment phase-down schedule, most production and use of HFCs will be eliminated over the coming decades. Other high-GWP ozone-depleting refrigerants are mostly phased out of new production under the Montreal Protocol, although large quantities still exist in refrigerant banks (Montreal Protocol on Substances That Deplete the Ozone Layer, 1987). 

Our achievable adoption values do not account for growth in the refrigerant bank over 2022 levels. Although refrigerant use is expected to grow substantially in the coming decades (IEA, 2023), we did not project future demand as part of our assessment. If HFC phaseout does not outpace refrigerant demand growth, emissions can increase despite more widespread adoption of this solution. Lowering the demand for refrigerant while ensuring that all people have access to refrigeration, heating, and cooling will be challenging.

Table 6. Range of achievable adoption levels for low-GWP refrigerants.

Unit: kt high-GWP refrigerant phased out

Current Adoption 440
Achievable – Low 5500
Achievable – High 5900
Adoption Ceiling 6900

Impacts

This solution has high potential climate impact due to both the quantity and high GWP of many current refrigerants. High-GWP refrigerant already phased out for low-GWP alternatives has an estimated current climate impact of 0.20 Gt CO₂‑eq/yr on a 100-yr basis (Table 7). If the Kigali Amendment HFC phasedown schedule is followed globally, we expect the achievable-adoption climate impact to be 2.5–2.7 Gt CO₂‑eq (100-yr)/yr. Reaching the adoption ceiling could potentially mitigate 3.2 Gt CO₂‑eq (100-yr)/yr. 

Due to the short lifetime of most high-GWP refrigerants, the climate benefit of phasing them out for alternatives is higher on a 20-year time horizon, making this solution highly impactful in the short-term. The use of low-GWP refrigerants currently saves an estimated 0.38 Gt CO₂‑eq (20-yr)/yr. The achievable 20-year impact is 4.7–5.0 Gt CO₂‑eq/yr, with a ceiling of 5.9 Gt CO₂‑eq/yr.

Since medium-GWP refrigerants are less effective at reducing emissions, the climate impacts are lower. If the same achievable adoption scenarios are reached but the effectiveness is calculated for medium-GWP refrigerants in commercial refrigeration, transport refrigeration, and stationary air conditioning applications, the climate impact reduces to 2.2–2.4 Gt CO₂‑eq (100-yr)/yr or 3.9–4.1 Gt CO₂‑eq (20-yr)/yr.

Our findings differ from some prominent literature estimates of the scale of current refrigerant emissions. The Green Cooling Initiative (n.d.) reports 1.4 Gt CO₂‑eq/yr in total direct refrigerant emissions in 2024. The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment (2023) estimates less than 1.0 Gt CO₂‑eq/yr in 2019. Expert estimates of emission reduction potential through 2050 are detailed under Evidence Base. We find potential for greater mitigation than these estimates of emissions. This difference could be due to our use of national self-reported emissions data, much of which did not specify sector or particular refrigerant type, leading to uncertainties in average GWPs and refrigerant release rates. These average GWPs and release rates were calculated using data from a small number of countries, primarily Annex I countries. This could overestimate effectiveness and climate impact if the actual global averages of these values are less than our calculations.

Table 7. Climate impact at different levels of adoption of low-GWP alternative refrigerants.

Unit: Gt CO₂‑eq/yr, 100-yr basis

Current Adoption 0.20
Achievable – Low 2.50
Achievable – High 2.70
Adoption Ceiling 3.20

Income and Work

Transitioning from HFCs to refrigerants with lower GWP can increase jobs (Colbourne et al., 2013; U.S. EPA, 2025). Reports from the Alliance for Responsible Atmospheric Policy and collaborators found that moving toward lower GWP refrigerants in the United States would increase jobs, increase manufacturing outputs of alternative refrigerants, and create more exports, strengthening the United States’ trade position (Inforum et al., 2019; JMS Consulting & Inforum, 2018). It is possible that using alternative refrigerants could lead to consumer savings on energy bills, depending on the alternative refrigerant, application, and equipment design (Colbourne et al., 2013; Purohit & Höglund-Isaksson, 2017; Shah et al., 2019; Zaelke & Borgford-Parnell, 2015). For example, an analysis of mobile air conditioning found that switching to an alternative refrigerant, such as R152a, can lead to high cost savings over its lifetime, and consumers in hotter climates would see the savings benefits (Blumberg et al., 2019). Since efficiency improvements are possible but not guaranteed in all cases, we do not consider this a guaranteed additional benefit. 

Land Resources

For a description of the benefits to land resources, please refer to Air Quality below. 

Air Quality

Some F-gases such as HFCs are considered per- and polyfluoroalkyl substances (PFAS) and can persist in the environment for centuries, posing serious human and ecosystem health risks (Figure 1) (Dimitrakopoulou et al., 2024; Fenton et al., 2021). PFAS can decompose in the atmosphere to produce trifluoroacetic acid (TFA), which can harm the environment and human health (UNEP, 2023). Possible impacts of high atmospheric TFA concentrations include acid rain, accumulation in terrestrial ecosystems in water and plant matter, and harmful effects on the environment and organisms (Chele et al., 2024; Hanson et al., 2024). Non-fluorinated alternative refrigerants would reduce the amount of PFAS pollution and reduce atmospheric TFA formation, lessening these harmful impacts. Some of these air quality benefits would also benefit indoor air quality because most refrigerants are used in buildings. Using alternative refrigerants avoids release of ozone-depleting substances such as HCFCs that can harm the ozone layer (Bolaji & Huan, 2013).

These benefits depend on the alternative refrigerant used – some low-GWP F-gas refrigerants such as HFOs are highly reactive, can be classified as PFAS, and can form TFA and other degradation products (Salvador et al., 2024). Therefore, the type of alternative refrigerant affects whether this is a benefit or a risk (see Risks below for more information). The thresholds at which these impacts occur are not well understood, and more research is needed to understand the potential harmful effects of TFA (Arp et al., 2024). 

Other

Permanence

There is a low risk of the emissions reductions for this solution being reversed. Each kt high-GWP refrigerant phased out for a lower-GWP alternative reduces the emissions from refrigerant release during manufacturing, transport, installation, operation, repair, and disposal of equipment. 

Additionality

This solution is additional when alternative refrigerant is used in applications that would have used HFCs or other high-GWP refrigerants in recent history. HFCs are not the baseline refrigerant in every scenario: hydrocarbons, for example, have been widely used in residential refrigeration and ammonia in industrial refrigeration for many years. 

In our analysis, we considered any path to adoption of alternative refrigerants to be part of its effectiveness at reducing GHG emissions. For example, we considered all HFC reductions mandated by policy to be considered additional over baseline HFC usage. However, some GHG accounting or crediting organizations would consider this regulatory additionality; the only emissions reductions that count as additional would be those not mandated by international, regional, and application-specific policy limits.

Some alternative refrigerants – including propane and ammonia – can react in the atmosphere to form polluting or toxic compounds (Chele et al., 2024). Low- and medium-GWP HFO or HFC refrigerants degrade into TFA, which is considered by some regulating bodies to be a PFAS, a class of chemicals with a proposed ban in Europe (European Chemicals Agency, 2023; European Environmental Bureau, 2025; Garavagno et al., 2024). Although TFA concentrations are currently low and impacts are minimal, increased HFO use could lead to greater accumulation, making it important to further study the potential risks (Chele et al., 2024; European Environmental Bureau, 2025; Hanson et al., 2024; Holland et al., 2021). Moreover, HFOs are made from high-GWP feedstocks, perpetuating the production and release of high-GWP chemicals (Booten et al., 2020; Chele et al., 2024). The use of other alternative refrigerant chemistries will reduce these risks (see Figure 1 and Additional Benefits).

Alternative refrigerants can be flammable (e.g., propane, ammonia) and toxic (e.g., ammonia). This potentially risks the well-being of people or property due to ignition, explosion, or refrigerant leaks (Shah et al., 2017). Minimizing leaks, reducing proximity to ignition sources, enhancing leak sensing, regulating safe charge sizes, and training installation and maintenance professionals are ways to lower this risk (Secop, 2018). Many alternative refrigerants are classified in ASHRAE safety group A2L, and these refrigerants have a low risk of ignition (Gradient, 2015; Imamura et al., 2015). Many countries have updated their standards in recent years to ensure safe use of low-GWP refrigerants, but adoption can be slowed if building codes do not allow for adoption (Heubes et al., 2012; UNEP, 2023).

Some specific technological solutions are required to avoid risks – for example, ammonia corrodes copper (Dräger, n.d.), and CO₂ refrigerant requires equipment and safety mechanisms that can handle its high operating pressure (Zanchi et al., 2019).

For particular alternative refrigerants and applications, switching to a lower-GWP refrigerant can reduce equipment efficiency (ASHRAE, 2009). Such a switch would decrease direct emissions due to reduction in refrigerant GWP, but would increase emissions associated with electricity generation.

Less efficient refrigerants may also require larger equipment and heavier masses of refrigerants, increasing the emissions for producing and transporting appliances. Fabris et al. (2024) reported that transport refrigeration systems using CO₂ refrigerant are heavier, leading to a 9.3% increase in emissions from fuel consumption during transport.

Reinforcing

Decreasing food loss and waste could require increases in cold storage capacity, especially in commercial, residential, and transport refrigeration (Babiker, 2017; Food and Agriculture Organization of the United Nations, 2019). Alternative refrigerants will lead to reduced GHG emissions from this new food refrigeration equipment, particularly for high-leakage systems such as supermarket refrigeration. However, if less food is produced to better manage food loss, this could lead to a decreased demand for cold storage (Dong et al., 2021).

Competing

Decreasing emissions from air conditioning technology would decrease the effectiveness of other building cooling solutions relative to single-building refrigerant-based air cooling units.

Using alternative refrigerants will decrease the CO₂‑eq emissions from released refrigerants. This means that management practices to reduce refrigerant release will save fewer CO₂‑eq emissions.

Consensus of effectiveness in reducing emissions: High

Phasing out high-GWP refrigerants for low or medium-GWP refrigerants is unquestionably effective at reducing emissions from refrigerant use.

In a report from two U.S. national laboratories, Booten et al. (2020) claim that systems using F-gas refrigerants for refrigeration and air conditioning are “the most difficult and impactful” innovation spaces for refrigerants. Zaelke and Borgford-Parnell (2015) asserted that reducing short-lived climate pollutants including HFCs “is the most effective strategy for constraining warming and associated impacts in the near term.” Utilizing low-GWP alternative refrigerants is a proven means to achieve this.

The IPCC Sixth Assessment (2023) cites the World Meteorological Organization (2018) and Höglund-Isaksson et al. (2017) in claiming that worldwide compliance with the Kigali Amendment schedule would reduce HFC emissions by 61% over baseline emissions by 2050. Velders et al. (2022) modeled future HFC emissions under the Kigali Amendment and found that these HFC reductions could save 3.1–4.4 Gt CO₂‑eq , 100-yr basis/yr by 2050. Dreyfus et al. (2020) estimate possible cumulative savings of 33–47 Gt CO₂‑eq (100-yr) through 2050, with an additional 53 Gt CO₂‑eq (100-yr) through 2060 if HFC phase-down is immediate.

Expert consensus is that the potential impact of alternative refrigerants will increase as a warming climate and increased population and development drive demand for higher use of cooling equipment (Campbell et al., 2018; Dreyfus et al., 2020; Petri & Caldeira, 2015). This will particularly be true for developing countries in already warm climates (Dong et al., 2021). 

The results presented in this document summarize findings from one review article, six original studies, two reports, one international treaty, two industry guidelines, one conference proceeding, and eight national GHG inventory submissions to the United Nations. This reflects current evidence from 34 countries, primarily Annex 1 countries as identified by the United Nations as well as China. We recognize this limited geographic scope creates bias, and hope this work inspires research and data sharing on this topic in underrepresented regions.

Take Action

Looking to get involved? Below are some key actions for this solution that can get you started, arranged according to different roles you may play in your professional or personal life.

These actions are meant to be starting points for involvement and are not intended to be prescriptive or necessarily suggest they are the most important or impactful actions to take. We encourage you to explore and get creative!

Lawmakers and Policymakers

  • Develop national cooling plans and integrate them into national climate plans.
  • Enact comprehensive policies that incentivize the lowest possible GWP refrigerants, penalize high-GWP refrigerants, and provide updated building code requirements.
  • Create government procurement policies that become stricter over time to mandate the use of alternative refrigerants or implement refrigerant GWP limits in government buildings and cooling systems.
  • Offer financial incentives such as subsidies, tax credits, and grants for using alternative refrigerants.
  • Implement the transition to alternative refrigerants while simultaneously working to improve equipment energy efficiency.
  • Implement an array of safety regulations that reduce the risk of leaks and exposure, such as restricting charge sizes, improving ventilation and leak sensors, and requiring certification for professionals.
  • Create free workforce training programs to improve safety around installation and maintenance.
  • Invest in R&D to improve availability, compatibility with existing equipment, and safety of alternative refrigerants.
  • Require detailed recordkeeping for vendors, contractors, and technicians to track and report on refrigerant types and amounts in use.
  • Develop refrigerant audit programs similar to energy audit programs.
  • Conduct consultations with national and local government agencies, businesses, schools, universities, farmers, healthcare professionals, research institutions, nonprofits, and the public to determine how best to transition local supply chains to alternative refrigerants.
  • Create certification schemes to identify which businesses utilize alternative refrigerants.
  • Offer educational resources, creating one-stop shops for information on alternative refrigerants and energy efficiency; offer demonstrations, highlighting their cost savings and climate benefits.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

Practitioners

  • Use alternative refrigerants and equipment that uses the lowest possible GWP refrigerant, and phase in alternative refrigerants throughout the rest of your supply chain.
  • Advocate for comprehensive policy plans that incentivize the lowest possible GWP refrigerants, penalize high-GWP refrigerants, and provide updated building code requirements.
  • Avoid venting or intentional releases of high-GWP refrigerants and conduct regular maintenance on equipment.
  • Maintain detailed records to track and report on refrigerant types and amounts in use.
  • Improve building, operations, and cooling designs to reduce demand for refrigerants.
  • Implement an array of safety protocols to reduce the risk of leaks and exposure, such as restricting charge sizes, improving ventilation and leak sensors, and ensuring only trained professionals service the equipment.
  • Take advantage of financial incentives such as subsidies, tax credits, and grants for using alternative refrigerants.
  • Participate in consultations with national and local government agencies, businesses, universities, farmers, healthcare professionals, research institutions, nonprofits, and the public to determine how best to transition local supply chains to alternative refrigerants.
  • Stay abreast of changing regulations, identify authoritative and trustworthy sources of legal and policy information, and invest in technology that stays ahead of the refrigerant transition curve.
  • Participate in certification schemes that identify which businesses utilize alternative refrigerants.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

Business Leaders

  • Establish time-bound, transparent targets for transitioning to alternative refrigerants.
  • Use alternative refrigerants and equipment that uses the lowest possible GWP refrigerant; pressure or incentivize suppliers to phase in and report on alternative refrigerants throughout your supply chain.
  • Take advantage of financial incentives such as subsidies, tax credits, and grants for using alternative refrigerants.
  • Maintain detailed records to track and report on refrigerant types and amounts in use within operations; request and maintain records from suppliers.
  • Improve building, operations, and cooling designs to reduce demand for refrigerants.
  • Participate in consultations with national and local government agencies, businesses, universities, farmers, healthcare professionals, research institutions, nonprofits, and the public to determine how best to transition local supply chains to alternative refrigerants.
  • Participate in certification schemes that identify which businesses utilize alternative refrigerants.
  • Advocate for comprehensive policy plans that incentivize the lowest possible GWP refrigerants, penalize high-GWP refrigerants, and provide updated building code requirements.
  • Advocate for bans on venting or intentional releases of high-GWP refrigerants, requirements for regular maintenance, and refrigerant or equipment tracking programs to help enforcement.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

Nonprofit Leaders

  • Ensure operations use alternative refrigerants and equipment that uses the lowest possible GWP refrigerant, if relevant.
  • Advocate for comprehensive policy plans that incentivize the lowest possible GWP refrigerants, penalize high-GWP refrigerants, and provide updated building code requirements.
  • Advocate for bans on venting or intentional releases of high-GWP refrigerants, requirements for regular maintenance, and refrigerant or equipment tracking programs to help enforcement.
  • Help develop national cooling plans and integrate them into national climate plans.
  • Work with public schools, health facilities, and other public venues to deploy alternative refrigerants.
  • Create free workforce training programs to improve safety around installation and maintenance.
  • Assist with technology transfer to low- and middle-income countries to help improve low-cost adoption.
  • Create public campaigns to advocate against dumping inefficient equipment in local markets – especially in low- and middle-income countries.
  • Help develop refrigerant audit programs similar to energy audit programs.
  • Participate in consultations with national and local government agencies, businesses, universities, farmers, healthcare professionals, research institutions, nonprofits, and the public to determine how best to transition local supply chains to alternative refrigerants.
  • Offer educational resources, creating one-stop shops for information on alternative refrigerants and energy efficiency; offer demonstrations, highlighting their cost savings and climate benefits.
  • Administer or participate in certification schemes that identify which businesses utilize alternative refrigerants.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

Investors

  • Ensure portfolio companies use or have a credible plan to use alternative refrigerants and phase in alternative refrigerants throughout the rest of their supply chain.
  • Ensure infrastructure investment projects leverage building, operations, and cooling designs that reduce demand for refrigerants.
  • Invest in start-ups working to improve and deploy alternative refrigeration technologies and refrigerant recycling.
  • Offer preferential loan agreements for developers utilizing alternative refrigerants and other climate-friendly practices.
  • Offer innovative financing methods such as microloans and green bonds to invest in projects that use alternative refrigerants.
  • Invest in R&D to improve availability, cost, compatibility with existing equipment, and safety of alternative refrigerants.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

Philanthropists and International Aid Agencies

  • Ensure operations use alternative refrigerants and equipment that uses the lowest possible GWP refrigerant, if relevant.
  • Advocate for comprehensive policy plans that incentivize the lowest possible GWP refrigerants, penalize high-GWP refrigerants, and provide updated building code requirements.
  • Advocate for bans on venting or intentional releases of high-GWP refrigerants, requirements for regular maintenance, and refrigerant or equipment tracking to help enforcement.
  • Invest in start-ups working to improve and deploy alternative refrigeration technologies.
  • Set requirements for alternative refrigerants when funding new construction.
  • Offer financing options such as grants, microloans, and green bonds to invest in projects that use alternative refrigerants.
  • Invest in R&D to improve availability, cost, compatibility with existing equipment, and safety of alternative refrigerants.
  • Help develop national cooling plans and integrate them into national climate plans.
  • Work with public schools, health facilities, and other public venues to deploy alternative refrigerants.
  • Create free workforce training programs to improve safety around installation and maintenance.
  • Assist with technology transfer to low- and middle-income countries to help improve adoption.
  • Create public campaigns to advocate against dumping inefficient equipment in local markets – especially in low- and middle-income countries.
  • Help develop refrigerant audit programs similar to energy audit programs.
  • Research other traditional methods of cooling and food storage, develop means of scaling relevant methods, and find practical means of integrating traditional methods with modern lifestyles.
  • Participate in consultations with national and local government agencies, businesses, universities, farmers, healthcare professionals, research institutions, nonprofits, and the public to determine how best to transition local supply chains to alternative refrigerants.
  • Offer educational resources, creating one-stop shops for information on alternative refrigerants and energy efficiency; offer demonstrations, highlighting their cost savings and climate benefits.
  • Participate in certification schemes that identify which businesses utilize alternative refrigerants.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

Thought Leaders

  • Advocate for comprehensive policy plans that incentivize the lowest possible GWP refrigerants, penalize high-GWP refrigerants, and provide updated building code requirements.
  • Advocate for bans on venting or intentional releases of high-GWP refrigerants, requirements for regular maintenance, and refrigerant or equipment tracking to help enforcement.
  • Help develop national cooling plans and integrate them into national climate plans.
  • Work with public schools, health facilities, and other public venues to deploy alternative refrigerants.
  • Assist with technology transfer to low- and middle-income countries to help improve adoption.
  • Create public campaigns to advocate against dumping inefficient equipment in local markets – especially in low- and middle-income countries.
  • Help develop refrigerant audit programs similar to energy audit programs.
  • Research other traditional methods of cooling and food storage, develop means of scaling relevant methods, and find practical means of integrating traditional methods with modern lifestyles.
  • Participate in consultations with national and local government agencies, businesses, universities, farmers, healthcare professionals, research institutions, nonprofits, and the public to determine how best to transition local supply chains to alternative refrigerants.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

Technologists and Researchers

  • Research and develop new low- and medium-GWP alternative refrigerants.
  • Find ways to optimize the charge size, cooling performance, and end-of-life management of alternative refrigerants.
  • Design better cooling and heat pump systems to reduce cost of installation and maintenance.
  • Develop software to track types and quantities of refrigerants in use.
  • Conduct R&D on improving cost-effectiveness, safety, and compatibility with existing equipment of alternative refrigerants.
  • Develop software for companies to model and simulate alternative refrigerants within various system configurations.
  • Find opportunities to achieve higher equipment efficiencies or other energy-saving designs, such as recovering and utilizing waste heat from CO₂ refrigerant systems.
  • Improve gas detection systems to improve safety protocols around alternative refrigerants.
  • Research other traditional methods of cooling and food storage; develop means of scaling relevant methods; find practical means of integrating traditional methods with modern lifestyles.

Further information:

Communities, Households, and Individuals

  • Use alternative refrigerants and equipment that uses the lowest possible GWP.
  • Explore and integrate other traditional methods of cooling and food storage, if relevant.
  • Advocate for comprehensive policy plans that incentivize the lowest possible GWP refrigerants, penalize high-GWP refrigerants, and provide updated building code requirements.
  • Advocate for bans on venting or intentional releases of high-GWP refrigerants, requirements for regular maintenance, and refrigerant or equipment tracking to help enforcement.
  • Work with public schools, health facilities, and other public venues to deploy alternative refrigerants.
  • Take advantage of financial incentives such as subsidies, tax credits, and grants for using alternative refrigerants.
  • Participate in consultations with national and local government agencies, businesses, universities, farmers, healthcare professionals, research institutions, nonprofits, and the public to determine how best to transition local supply chains to alternative refrigerants.
  • Create, support, or join networks or partnerships dedicated to advancing and deploying alternative refrigerants.

Further information:

“Take Action” Sources

References

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Shah, N., Khanna, N., Karali, N., Park, W. Y., Qu, Y., & Zhou, N. (2017). Opportunities for simultaneous efficiency improvement and refrigerant transition in air conditioning. Lawrence Berkeley National Laboratory. Link to source: https://cooling.lbl.gov/publications/opportunities-simultaneous-efficiency 

Shah, N., Wei, M., Letschert, V., & Phadke, A. (2015). Benefits of leapfrogging to superefficiency and low global warming potential refrigerants in room air conditioning. Lawrence Berkeley National Laboratory. Link to source: https://www.osti.gov/servlets/purl/1235571 

Shah, N., Wei, M., Letschert, V., & Phadke, A. (2019). Benefits of energy efficient and low-global warming potential refrigerant cooling equipment. Lawrence Berkeley National Laboratory. Link to source: https://cooling.lbl.gov/publications/benefits-energy-efficient-and-low 

Sherry, D., Nolan, M., Seidel, S., & Andersen, S. O. (2017). HFO-1234yf: An examination of projected long-term costs of production. Nolan Sherry & Associates, Center for Climate and Energy Solutions, Institute for Governance and Sustainable Development. Link to source: https://www.c2es.org/wp-content/uploads/2017/04/hfo-1234yf-examination-projected-long-term-costs-production.pdf 

Smith, C., Nicholls, Z. R. J., Armour, K., Collins, W., Forster, P., Meinshausen, M., Palmer, M. D., & Watanabe, M. (2021). The Earth’s energy budget, climate feedbacks, and climate sensitivity supplementary material. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Link to source: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter07_SM.pdf 

Sustainable Purchasing Leadership Council Climate Friendly Refrigerant Action Team. (2021). Recommendations for climate friendly refrigerant management and procurement. Link to source: https://www.igsd.org/publications/recommendations-for-climate-friendly-refrigerant-management-and-procurement/ 

Trevisan, T. (2023, July 3). Overview of PFAS refrigerants used in HVAC&R and relevance of refrigerants in the PFAS Restriction Intention. UN Montreal Protocol 45th OEWG, Bangkok. Link to source: https://ozone.unep.org/system/files/documents/OEWG45_ATMO_sidevent.pdf 

United Nations Development Programme. (2022). Guidance note: Assessing greenhouse gas emissions from refrigerants use in UNDP operations. Link to source: https://www.undp.org/sites/g/files/zskgke326/files/2022-07/Refrigerants%20methodology%20version%20July%202022.pdf 

United Nations Environment Programme. (2023). Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee: 2022 assessment report. Link to source: https://ozone.unep.org/system/files/documents/RTOC-assessment%20-report-2022.pdf 

United Nations Environment Programme & ASHRAE. (2025). Update on new refrigerants designations and safety classifications June 2025. Link to source: https://www.ashrae.org/file%20library/professional%20development/ashrae-unep/unep---ashrae-factsheet--english.pdf 

United Nations Framework Convention on Climate Change. (2023). National inventory submissions, Annex 1 parties [Data set]. Link to source: https://unfccc.int/ghg-inventories-annex-i-parties/2023  

U.S. Environmental Protection Agency. (2011). Transitioning to low-GWP alternatives in transport refrigeration. Link to source: https://www.epa.gov/sites/default/files/2015-07/documents/transitioning_to_low-gwp_alternatives_in_transport_refrigeration.pdf 

U.S. Environmental Protection Agency. (2025). Frequent questions on the phasedown of hydrofluorocarbons. Link to source: https://www.epa.gov/climate-hfcs-reduction/frequent-questions-phasedown-hydrofluorocarbons 

Velders, G. J. M., Daniel, J. S., Montzka, S. A., Vimont, I., Rigby, M., Krummel, P. B., Muhle, J., O’Doherty, S., Prinn, R. G., Weiss, R. F., & Young, D. (2022). Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies. Atmospheric Chemistry and Physics, 22(9), 6087–6101. Link to source: https://doi.org/10.5194/acp-22-6087-2022 

Velders, G. J. M., Fahey, D. W., Daniel, J. S., Andersen, S. O., & McFarland, M. (2015). Future atmospheric abundances and climate forcings from scenarios of global and regional hydrofluorocarbon (HFC) emissions. Atmospheric Environment, 123, 200–209. Link to source: https://doi.org/10.1016/j.atmosenv.2015.10.071 

World Meteorological Organization. (2018). Executive summary: Scientific assessment of ozone depletion: 2018 (Report No. 58). Link to source: https://ozone.unep.org/sites/default/files/2019-04/SAP-2018-Assessment-report-ES-rev%20%281%29.pdf 

Zaelke, D., & Borgford-Parnell, N. (2015). The importance of phasing down hydrofluorocarbons and other short-lived climate pollutants. Journal of Environmental Studies and Sciences, 5(2), 169–175. Link to source: https://doi.org/10.1007/s13412-014-0215-7 

Zanchi, V., Boban, L., & Soldo, V. (2019). Refrigerant options in the near future. Journal of Sustainable Development of Energy, Water and Environment Systems, 7(2), 293–304. Link to source: https://doi.org/10.13044/j.sdewes.d6.0250 

Credits

Lead Fellow

  • Sarah Gleeson, Ph.D.

Contributors

  • Ruthie Burrows, Ph.D.

  • James Gerber, Ph.D.

  • Daniel Jasper

  • Alex Sweeney

Internal Reviewers

  • Aiyana Bodi

  • James Gerber, Ph.D.

  • Hannah Henkin

  • Heather McDiarmid, Ph.D.

  • Ted Otte

  • Amanda D. Smith, Ph.D.

Methods and Supporting Data

Methods and Supporting Data

Comments / Questions

  • Greenhouse gas quantity expressed relative to CO₂ with the same warming impact over 100 years, calculated by multiplying emissions by the 100-yr GWP for the emitted gases.

  • Greenhouse gas quantity expressed relative to CO₂ with the same warming impact over 20 years, calculated by multiplying emissions by the 20-yr GWP for the emitted gases.

  • 8th World Congress on Conservation Agriculture

  • Reducing greenhouse gas concentrations in the atmosphere by preventing or reducing emissions.

  • The process of increasing acidity.

  • The extent to which emissions reduction or carbon removal is above and beyond what would have occurred without implementing a particular action or solution.

  • An upper limit on solution adoption based on physical or technical constraints, not including economic or policy barriers. This level is unlikely to be reached and will not be exceeded.

  • The quantity and metric to measure implementation for a particular solution that is used as the reference unit for calculations within that solution.

  • A composting method in which organic waste is processed in freestanding piles that can be aerated actively with forced air or passively by internal convection.

  • The interactions of aerodynamic forces and flexible structures, often including the stucture's control system.

  • A process in which microbes break down organic materials in the presence of oxygen. This process converts food and green waste into nutrient-rich compost.

  • Farming practices that work to create socially and ecologically sustainable food production.

  • Addition of trees and shrubs to crop or animal farming systems.

  • Spread out the cost of an asset over its useful lifetime.

  • A crop that live one year or less from planting to harvest; also called annual.

  • aerated static piles

  • black carbon

  • Made from material of biological origin, such as plants, animals, or other organisms.

  • A renewable energy source generated from organic matter from plants and/or algae.

  • An energy source composed primarily of methane and CO₂ that is produced by microorganisms when organic matter decomposes in the absence of oxygen.

  • Carbon stored in biological matter, including soil, plants, fungi, and plant products (e.g., wood, paper, biofuels). This carbon is sequestered from the atmosphere but can be released through decomposition or burning.

  • Living or dead renewable matter from plants or animals, not including organic material transformed into fossil fuels. Peat, in early decay stages, is partially renewable biomass.

  • Biogas refined to the same quality as natural gas. CO₂ and impurities are removed, and the biomethane can be distributed and used in existing natural gas technologies.
     

  • A type of carbon sequestration that captures carbon from CO₂ via photosynthesis and stores it in soils, sediments, and biomass, distinct from sequestration through chemical or industrial pathways.

  • A climate pollutant, also called soot, produced from incomplete combustion of organic matter, either naturally (wildfires) or from human activities (biomass or fossil fuel burning).

  • A secure, decentralized way of digitally tracking transactions that could be used to improve the transparency and efficiency of carbon markets. 

  • High-latitude (>50°N or >50°S) climate regions characterized by short growing seasons and cold temperatures.

  • The components of a building that physically separate the indoors from the outdoor environment.

  • Businesses involved in the sale and/or distribution of solution-related equipment and technology, and businesses that want to support adoption of the solution.

  • A chemical reaction involving heating a solid to a high temperature; to make cement clinker, limestone is calcined into lime in a process that requires high heat and produces CO₂.

  • The ratio of the actual electricity an energy technology generates over a period of time to the maximum it could have produced if it operated at full capacity continuously.

  • A four-wheeled passenger vehicle.

  • Average number of people traveling in a car per trip.

  • Technologies that collect CO₂ before it enters the atmosphere, preventing emissions at their source. Collected CO₂ can be used onsite or in new products, or stored long term to prevent release.

  • A greenhouse gas that is naturally found in the atmosphere. Its atmospheric concentration has been increasing due to human activities, leading to warming and climate impacts.

  • Total GHG emissions resulting from a particular action, material, technology, or sector.

  • Amount of GHG emissions released per activity or unit of production. 

  • A marketplace where carbon credits are purchased and sold. One carbon credit represents activities that avoid, reduce, or remove one metric ton of GHG emissions.

  • A colorless, odorless gas released during the incomplete combustion of fuels containing carbon. Carbon monoxide can harm health and be fatal at high concentrations.

  • The time it takes for the emissions reduction from a measure to equal the emissions invested in implementing the measure.

  • Activities or technologies that pull CO₂ out of the atmosphere, including enhancing natural carbon sinks and deploying engineered sinks.

  • Long-term storage of carbon in soils, sediment, biomass, oceans, and geologic formations after removal of CO₂ from the atmosphere or CO₂ capture from industrial and power generation processes.

  • carbon capture and storage

  • carbon capture, utilization, and storage

  • A binding ingredient in concrete responsible for most of concrete’s life-cycle emissions. Cement is made primarily of clinker mixed with other mineral components.

  • chlorofluorocarbon

  • methane

  • Energy sources that have little to no negative environmental or climate impacts during operation relative to fossil fuel–based energy sources.

  • Gases or particles that have a planet-warming effect when released to the atmosphere. Some climate pollutants also cause other forms of environmental damage.

  • A binding ingredient in cement responsible for most of the life-cycle emissions from cement and concrete production.

  • A waste management process where waste is made into the same original product, preserving quality and value so materials can be reused multiple times while keeping resources in continuous use.

  • carbon monoxide

  • Neighbors, volunteer organizations, hobbyists and interest groups, online communities, early adopters, individuals sharing a home, and private citizens seeking to support the solution.

  • A solution that potentially lowers the benefit of another solution through reduced effectiveness, higher costs, reduced or delayed adoption, or diminished global climate impact.

  • A farming system that combines reduced tillage, cover crops, and crop rotations.

  • A risk-sharing financial agreement in which two parties (e.g., renewable generator, government) guarantee a fixed price (e.g., electricity price). If market prices fluctuate, one party pays the other the difference.

  • carbon dioxide

  • A  measure standardizing the warming effects of greenhouse gases relative to CO₂. CO₂-eq is calculated as quantity (metric tons) of a particular gas multiplied by its GWP.

  • carbon dioxide equivalent

  • Plant materials left over after a harvest, such as stalks, leaves, and seed husks.

  • A granular material made by crushing broken or waste glass.

  • direct air capture

  • Financial agreements in which government creditors forgive a portion of debt in exchange for specific conservation commitments.

  • The process of cutting greenhouse gas emissions (primarily CO₂) from a particular sector or activity.

  • An industrial process that removes printing ink from used or waste paper fibers, creating clean pulp that can be turned into new paper products.

  • A solution that works slower than gradual solutions and is expected to take longer to reach its full potential.

  • Microbial conversion of nitrate into inert nitrogen gas under low-oxygen conditions, which produces the greenhouse gas nitrous oxide as an intermediate compound.

  • Greenhouse gas emissions produced as a direct result of the use of a technology or practice.

  • A window consisting of two glass panes separated by a sealed gap and typically filled with air or an inert gas to improve the heat flow resistance.

  • A waste management system that transforms waste into different products of lower quality and value, making materials harder to recycle again and limiting reuse.

  • European Energy Agency

  • Ability of a solution to reduce emissions or remove carbon, expressed in CO₂-eq per installed adoption unit. Effectiveness is quantified per year when the adoption unit is cumulative over time.

  • A process that uses electric current to drive a reaction, such as using electricity to split water molecules into hydrogen and oxygen.

  • Greenhouse gas emissions accrued over the lifetime of a material or product, including as it is produced, transported, used, and disposed of.

  • Solutions that work faster than gradual solutions, front-loading their impact in the near term.

  • Methane produced by microbes in the digestive tracts of ruminant livestock, such as cattle, sheep and goats.

  • U.S. Environmental Protection Agency

  • expanded polystyrene

  • Environmental Research & Education Foundation

  • environmental, social, and governance

  • exchange-traded fund

  • A process triggered by an overabundance of nutrients in water, particularly nitrogen and phosphorus, that stimulates excessive plant and algae growth and can harm aquatic organisms.

  • Electric vehicle

  • An ecological process that releases water into the atmosphere as a gas from soil and ice (evaporation) and plants (transpiration).

     

  • The scientific literature that supports our assessment of a solution's effectiveness.

  • A group of human-made molecules that contain fluorine atoms. They are potent greenhouse gases with GWPs that can be hundreds to thousands times higher than CO₂.

  • Food, agriculture, land, and ocean

  • Food and Agriculture Organization of the United Nations

  • feed conversion ratio

  • The efficiency with which an animal converts feed into increased body mass, measured as the ratio of the weight of the feed given to weight gain. Lower FCR means less feed for the same growth.

  • Raw material inputs for manufacturing, processing, and managing waste.

  • Containing or consisting of iron.

  • A measure of fishing activity over time and area, commonly measured by number of trips, vessel time, or gear deployed.

  • food loss and waste

  • Food discarded during pre-consumer supply chain stages, including production, harvest, and processing.

  • Food discarded during pre-consumer supply chain stages, including production, harvest, and processing, along with food discarded wt the retail and consumer stages of the supply chain.

  • Food discarded at the retail and consumer stages of the supply chain.

  • Combustible materials found in Earth's crust that can be burned for energy, including oil, natural gas, and coal. They are formed from decayed organisms through prehistoric geological processes.

  • Free, prior, and informed consent

  • A principled process of working with Indigenous communities that requires consent from Indigenous peoples for any decision, action, or activity that impacts their community and/or lands.

  • Unintentional leaks of gases or vapor into the atmosphere.

  • Unintentional leaks of gases or vapor into the atmosphere.

  • A group of countries representing the majority of the world's population, trade, and GDP. There are 19 member countries plus the European Union and the African Union

  • greenhouse gas

  • gigajoule or billion joules

  • The glass layers or panes in a window.

  • A measure of how effectively a gas traps heat in the atmosphere relative to CO₂. GWP converts greenhouse gases into CO₂-eq emissions based on their 20- or 100-year impacts.

  • A solution that has a steady impact on the atmosphere. Effectiveness is expected to be constant over time rather than having a higher impact in the near or long term.

  • A fixed income debt instrument focused on sustainable projects. Green bonds work in the same manner as traditional bonds and may be issued by corporations, financial institutions, and governments.

  • Biomass discarded during landscaping and gardening.

  • A gas that traps heat in the atmosphere, contributing to climate change.

  • The makeup of electricity generation on a power grid, showing the share contributed by various energy sources (e.g., coal, natural gas, nuclear, wind, solar, hydro) relative to total electricity production.

  • metric gigatons or billion metric tons

  • global warming potential

  • hectare

  • household air pollution

  • hydrochlorofluorocarbon

  • Number of years a person is expected to live without disability or other limitations that restrict basic functioning and activity.

  • A unit of land area comprising 10,000 square meters, roughly equal to 2.5 acres.

  • Hybrid electric car

  • hydrofluorocarbon

  • hydrofluoroolefin

  • hydrofluoroolefin

  • Particles and gases released from use of polluting fuels and technologies such as biomass cookstoves that cause poor air quality in and around the home.

  • heating, ventilation, air conditioning, and refrigeration

  • Organic compounds that contain hydrogen and carbon.

  • Human-made F-gases that contain hydrogen, fluorine, and carbon. They typically have short atmospheric lifetimes and GWPs hundreds or thousands times higher than CO₂. 

  • Human-made F-gases that contain hydrogen, fluorine, and carbon, with at least one double bond. They have low GWPs and can be climate-friendly alternatives to HFC refrigerants.

  • Hydrogen is a gas that can be a fuel, feedstock, or means of storing energy. It generates water instead of GHG when burned, but the process of producing it can emit high levels of GHGs. 

  • Hydrogen is a gas that can be a fuel, feedstock, or means of storing energy. It generates water instead of GHG when burned, but the process of producing it can emit high levels of GHGs. 

  • A recycling process that separates fibers from contaminants for reuse. Paper or cardboard is mixed with water to break down fibrous materials into pulp.

  • internal combustion engine

  • International Energy Agency

  • Aerobic decomposition of organic waste in a sealed container or bin/bay system. 

  • Greenhouse gas emissions produced as a result of a technology or practice but not directly from its use.

  • Device used to power vehicles by the intake, compression, combustion, and exhaust of fuel that drives moving parts.

  • The annual discount rate that balances net cash flows for a project over time. Also called IRR, internal rate of return is used to estimate profitability of potential investments.

  • Individuals or institutions willing to lend money in search of a return on their investment.

  • Intergovernmental Panel on Climate Change

  • Indigenous peoples’ land

  • Integrated pest management.

  • internal rate of return

  • International Union for Conservation of Nature

  • The most comprehensive global list of species threatened with extinction, maintained by the International Union for Conservation of Nature.

  • International agreement adopted in 2016 to phase down the use of high-GWP HFC F-gases over the time frame 2019–2047.

  • A measure of energy equivalent to the energy delivered by 1,000 watts of power over one hour.

  • kiloton or one thousand metric tons

  • kilowatt-hour

  • A land-holding system, e.g. ownership, leasing, or renting. Secure land tenure means farmers or other land users will maintain access to and use of the land in future years.

  • Gases, mainly methane and CO₂, created by the decomposition of organic matter in the absence of oxygen.

  • levelized cost of electricity

  • leak detection and repair

  • Regular monitoring for fugitive methane leaks throughout oil and gas, coal, and landfill sector infrastructure and the modification or replacement of leaking equipment.

  • Relocation of emissions-causing activities outside of a mitigation project area rather than a true reduction in emissions.

  • The rate at which solution costs decrease as adoption increases, based on production efficiencies, technological improvements, or other factors.

  • Percent decrease in costs per doubling of adoption.

  • A metric describing the expected break-even cost of generating electricity per megawatt-hour ($/MWh), combining costs related to capital, operation, and fuel (if used) and dividing by total output over the generator's lifetime.

  • landfill gas

  • Greenhouse gas emissions from the sourcing, production, use, and disposal of a technology or practice.

  • The total weight of an organism before any meat processing.

  • low- and middle-income countries

  • liquefied petroleum gas

  • land use change

  • A measure of the amount of light produced by a light source per energy input.

  • live weight

  • marginal abatement cost curve

  • Livestock grazing practices that strategically manage livestock density, grazing intensity, and timing. Also called improved grazing, these practices have environmental, soil health, and climate benefits, including enhanced soil carbon sequestration.

  • A tool to measure and compare the financial cost and abatement benefit of individual actions based on the initial and operating costs, revenue, and emission reduction potential.

  • Defined by the International Union for Conservation of Nature as: "A clearly defined geographical space, recognised, dedicated and managed, through legal or other effective means, to achieve the long-term conservation of nature with associated ecosystem services and cultural values." References to PAs here also include other effective area-based conservation measures defined by the IUCN. 

  • A facility that receives recyclable waste from residential, commercial, and industrial sources; separates, processes, and prepares them; and then sells them to manufacturers for reuse in new products.

  • A measure of energy equivalent to the energy delivered by one million watts of power over one hour.

  • A greenhouse gas with a short lifetime and high GWP that can be produced through a variety of mechanisms including the breakdown of organic matter.

  • A measure of mass equivalent to 1,000 kilograms (~2,200 lbs).

  • million hectares

  • Soils mostly composed of inorganic materials formed through the breakdown of rocks. Most soils are mineral soils, and they generally have less than 20% organic matter by weight.

  • A localized electricity system that independently generates and distributes power. Typically serving limited geographic areas, mini-grids can operate in isolation or interconnected with the main grid.

  • Reducing the concentration of greenhouse gases in the atmosphere by cutting emissions or removing CO₂.

  • megajoule or one million joules

  • Percent of trips made by different passenger and freight transportation modes.

  • Marine Protected Area

  • materials recovery facility

  • Municipal solid waste

  • megaton or million metric tons

  • Materials discarded from residential and commercial sectors, including organic waste, glass, metals, plastics, paper, and cardboard.

  • megawatt

  • Megawatt-hour

  • micro wind turbine

  • square meter kelvins per watt (a measure of thermal resistance, also called R-value)

  • nitrous oxide

  • The enclosed housing at the top of a wind turbine tower that contains the main mechanical and electrical components of the turbine.

  • A commitment from a country to reduce national emissions and/or sequester carbon in alignment with global climate goals under the Paris Agreement, including plans for adapting to climate impacts.

  • A gaseous form of hydrocarbons consisting mainly of methane.

  • Chemicals found in nature that are used for cooling and heating, such as CO₂, ammonia, and some hydrocarbons. They have low GWPs and are ozone friendly, making them climate-friendly refrigerants.

  • Microbial conversion of ammonia or ammonium to nitrite and then to nitrate under aerobic conditions.

  • A group of air pollutant molecules composed of nitrogen and oxygen, including NO and NO₂.

  • A greenhouse gas produced during fossil fuel combustion and agricultural and industrial processes. N₂O is hundreds of times more potent than CO₂ at trapping atmospheric heat, and it depletes stratospheric ozone.

  • Metals or alloys that do not contain significant amounts of iron.

  • Social welfare organizations, civic leagues, social clubs, labor organizations, business associations, and other not-for-profit organizations.

  • A material or energy source that relies on resources that are finite or not naturally replenished at the rate of consumption, including fossil fuels like coal, oil, and natural gas.

  • nitrogen oxides

  • nitrous oxide

  • The process of increasing the acidity of seawater, primarily caused by absorption of CO₂ from the atmosphere.

  • Organisation for Economic Co-operation and Development

  • An agreement between a seller who will produce future goods and a purchaser who commits to buying them, often used as project financing for producers prior to manufacturing.

  • Waste made of plant or animal matter, including food waste and green waste.

  • organic waste

  • Protected Area

  • Productive use of wet or rewetted peatlands that does not disturb the peat layer, such as for hunting, gathering, and growing wetland-adapted crops for food, fiber, and energy.

  • A legally protected area that lacks effective enforcement or management, resulting in minimal to no conservation benefit.

  • Airborne particles composed of solids and liquids.

  • A measure of transporting one passenger over a distance of one kilometer.

  • Incentive payments to landowners or managers to conserve natural resources and promote healthy ecological functions or ecosystem services.

  • Small, hardened pieces of plastic made from cooled resin that can be melted to make new plastic products.

  • The longevity of any greenhouse gas emission reductions or removals. Solution impacts are considered permanent if the risk of reversing the positive climate impacts is low within 100 years.

  • Payments for ecosystem services

  • A mixture of hydrocarbons, small amounts of other organic compounds, and trace amounts of metals used to produce products such as fuels or plastics.

  • Per- and polyfluoroalkyl substances, a class of synthetic chemicals that do not degrade easily in the environment. They can pollute the environment and can have negative impacts on human health.

  • Reduce the use of a material or practice over time.

  • Eliminate the use of a material or practice over time.

  • Plug-in hybrid electric car

  • Private, national, or multilateral organizations dedicated to providing aid through in-kind or financial donations.

  • An atmospheric reaction among sunlight, VOCs, and nitrogen oxide that leads to ground-level ozone formation. Ground-level ozone, a component of smog, harms human health and the environment.

  • The process by which sunlight is converted into electricity. When light hits certain materials, such as those in solar panels, it mobilizes electrons, creating an electric current.

  • polyisocyanurate

  • The adjustment of turbine blade angles around their long axis in which a control system rotates blades slightly forward or backward to regulate wind capture and optimize electricity generation.

  • passenger kilometer

  • particulate matter

  • Particulate matter 2.5 micrometers or less in diameter that can harm human health when inhaled.

  • Elected officials and their staff, bureaucrats, civil servants, regulators, attorneys, and government affairs professionals.

  • System in a vehicle that generates power and delivers it to the wheels. It typically includes an engine and/or motor, transmission, driveshaft, and differential.

  • Purchase Power Agreement.

  • People who most directly interface with a solution and/or determine whether the solution is used and/or available. 

  • A substance that is the starting material for a chemical reaction that forms a different substance.

  • Extraction of naturally occurring resources from the Earth, including mining, logging, and oil and gas refining. These resources can be used in raw or minimally processed forms to produce materials.

  • The process of converting inorganic matter, including carbon dioxide, into organic matter (biomass), primarily by photosynthetic organisms such as plants and algae.

  • Defined by the International Union for the Conservation of Nature as "A clearly defined geographical space, recognised, dedicated and managed, through legal or other effective means, to achieve the long-term conservation of nature with associated ecosystem services and cultural values". References to PAs here also include other effective area-based conservation measures defined by the IUCN. 

  • A process that separates and breaks down wood and other raw materials into fibers that form pulp, the base ingredient for making paper products.

  • polyurethane

  • Long-term contract between a company (the buyer) and a renewable energy producer (the seller).

  • photovoltaic

  • research and development

  • A situation in which improvements in efficiency or savings lead to consumers increasing consumption, partially or fully offsetting or exceeding the emissions or cost benefits.

  • renewable energy certificate

  • Chemical or mixture used for cooling and heating in refrigeration, air conditioning, and heat pump equipment. Refrigerants absorb and release heat as they move between states under changing pressure.

  • The amount of refrigerant needed for a particular refrigeration, air conditioning, or heat pump system.

  • A group of approaches to farming and ranching that emphasizes enhancing the health of soil by restoring its carbon content and providing other benefits to the farm and surrounding ecosystem.

  • A solution that can increase the beneficial impact of another solution through increased effectiveness, lower costs, improved adoption, enhanced global climate impact, and/or other benefits to people and nature.

  • A material or energy source that relies on naturally occuring and replenishing resources such as plant matter, wind, or sunlight.

  • A market-based instrument that tracks ownership of renewable energy generation.

  • The moldable form of raw plastic material, created by melting down waste or virgin plastics and serving as the building block for creating new plastic goods.

  • A class of animals with complex stomachs that can digest grass. Most grazing livestock are ruminants including cows, sheep, and goats along with several other species.

  • sustainable aviation fuel

  • A wetland ecosystem regularly flooded by tides and containing salt-tolerant plants, such as grasses and herbs.

  • Very large or small numbers are formatted in scientific notation. A positive exponent multiplies the number by powers of ten; a negative exponent divides the number by powers of ten.

  • Seasonal coefficient of performance

  • Sustainable Development Goals

  • Average units of heat energy released for every unit of electrical energy consumed, used to measure heat pump efficiency.

  • A practice in which multiple utility companies own and operate high-voltage power lines, sharing both costs and benefits.

  • A window consisting of one glass pane without any additional insulating layers.

  • Small-scale family farmers and other food producers, often with limited resources, usually in the tropics. The average size of a smallholder farm is two hectares (about five acres).

  • soil organic carbon

  • Carbon stored in soils, including both organic (from decomposing plants and microbes) and inorganic (from carbonate-containing minerals).

  • Carbon stored in soils in organic forms (from decomposing plants and microbes). Soil organic carbon makes up roughly half of soil organic matter by weight.

  • Biologically derived matter in soils, including living, dead, and decayed plant and microbial tissues. Soil organic matter is roughly half carbon on a dry-weight basis.

  • soil organic matter

  • A substance that takes up another liquid or gas substance, either by absorbtion or adsorption.

  • sulfur oxides

  • sulfur dioxide

  • The rate at which a climate solution physically affects the atmosphere after being deployed. At Project Drawdown, we use three categories: emergency brake (fastest impact), gradual, or delayed (slowest impact).

  • Climate regions between latitudes 23.4° to 35° above and below the equator characterized by warm summers and mild winters.

  • A polluting gas produced primarily from burning fossil fuels and industrial processes that directly harms the environment and human health.

  • A group of gases containing sulfur and oxygen that predominantly come from burning fossil fuels. They contribute to air pollution, acid rain, and respiratory health issues.

  • Processes, people, and resources involved in producing and delivering a product from supplier to end customer, including material acquisition.

  • Sport utility vehicle

  • metric ton

  • metric tons

  • Technology developers, including founders, designers, inventors, R&D staff, and creators seeking to overcome technical or practical challenges.

  • Climate regions between 35° to 50° above and below the equator characterized by moderate mean annual temperatures and distinct seasons, with warm summers and cold winters.

  • A measure of energy equivalent to the energy delivered by one trillion watts of power over one hour.

  • trifluoroacetic acid

  • trifluoroacetic acid

  • A measure of how well a material prevents heat flow, often called R-value or RSI-value for insulation. A higher R-value means better thermal performance.

  • Individuals with an established audience for their work, including public figures, experts, journalists, and educators.

  • Charges for disposal of materials paid to facility operators. Fees can be charged per ton of waste disposed or based on economic indicators such as the Consumer Price Index.

  • A window consisting of three panes of glass separated by two insulating inert gas-filled layers, providing more heat flow resistance than single or double glazing.

  • Low-latitude (23.4°S to 23.4°N) climate regions near the Equator characterized by year-round high temperatures and distinct wet and dry seasons.

  • Terawatt, equal to 1,000 gigawatts

  • terawatt-hour

  • United Nations

  • United Nations Environment Programme

  • U.S. Composting Council

  • Self-propelled machine for transporting passengers or freight on roads.

  • A measure of one vehicle traveling a distance of one kilometer.

  • Aerobic decomposition of organic waste by earthworms and microorganisms.

  • vehicle kilometer

  • volatile organic compound

  • Gases made of organic, carbon-based molecules that are readily released into the air from other solid or liquid materials. Some VOCs are greenhouse gases or can harm human health.

  • watt (a measure of power or energy transfer.)

  • Landscape waste, storm debris, wood processing residues, and recovered post-consumer wood.

  • A measure of power equal to one joule per second.

  • Aerobic decomposition of organic waste in long, narrow rows called windrows. Windrows are generally twice as long as they are wide.

  • A subset of forest ecosystems that may have sparser canopy cover,  smaller-stature trees, and/or trees characterized by basal branching rather than a single main stem.

  • extruded polystyrene

  • The rotation of the nacelle (the enclosed housing at the top of a wind turbine tower that contains the main mechanical and electrical components of the turbine) so that the rotor blades are always facing directly into the wind.

  • year

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