Seaweed (also called macroalgae) ecosystem restoration involves the reestablishment of wild red, brown, and green seaweed through interventions that recover degraded, damaged, or destroyed seaweed ecosystems. Healthy seaweed ecosystems remove CO₂ from the water column and convert it into biomass through photosynthesis, allowing additional CO₂ to be taken up in the ocean from the atmosphere. Some of this biomass carbon ends up sequestered, either on-site in sediment or off-site in the deep sea or at the seafloor. Advantages include the widespread human and environmental benefits associated with restored, healthy seaweed ecosystems. Disadvantages include its unclear effectiveness and climate impact, as well as its potentially high costs and difficulty of adoption at scale. Currently, we conclude that we should “Keep Watching” this solution.
Based on our analysis, the climate impact of restoring seaweed ecosystems is unclear but likely to be low. While restoration offers important ecological benefits, its effectiveness in removing carbon is understudied, and the implementation costs may be prohibitively high, but require further research. Therefore, we conclude that Restore Seaweed Ecosystems is a solution to “Keep Watching.”
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | No |
| Effective | Does it consistently work? | ? |
| Impact | Is it big enough to matter? | ? |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | No |
Seaweed ecosystem restoration is the deliberate action of reestablishing seaweed in degraded, damaged, or destroyed ecosystems. Seaweed removes CO₂ from seawater through photosynthesis, which allows the ocean to absorb additional CO₂ from the atmosphere. Some of the fixed carbon can be sequestered through export to the deep sea or burial at the seafloor, while a portion may also persist as carbon forms that resist degradation even in the surface ocean. Restoration of seaweed ecosystems helps restore biomass and therefore the productivity of these ecosystems, which can enhance their sequestration capacity. Restoration can occur in a number of ways, but commonly includes transplanting adults, controlling grazers, building artificial reefs, seeding with propagules or spores, remediating pollution, removing competitive species, and culturing. Most restoration efforts have focused on canopy-forming species, such as giant kelp (Macrocystis pyrifera).
Seaweed ecosystem restoration can be somewhat effective, with nearly 60% of restoration efforts achieving survival rates of over 50%. The first large-scale restoration is thought to have occurred in Japan in the late 1800s. Still, few projects have been implemented at scale, with most restoration efforts below 0.1 ha in size. Moreover, little data exist to evaluate the effectiveness of restored seaweed ecosystems at removing carbon. While theoretically, they should regain functional equivalence to intact systems, this requires further research. The extent of lost and degraded seaweed ecosystems is also poorly understood, making it unclear how restoration efforts might be scaled globally. Additionally, the air-to-sea transfer of CO₂ to replace the CO₂ taken up by photosynthesis in the ocean is not always efficient, meaning removal in the water column may not always translate to equivalent atmospheric CO₂ removal. However, this aspect of effectiveness also remains understudied. Consequently, the climate impact of restoration is uncertain.
Healthy seaweed ecosystems provide a range of ecological benefits. Seaweed can help buffer against ocean acidification in some places as functional systems better regulate pH. These systems also provide complex habitats that support a wide range of marine life, such as fish and invertebrates, so restoring seaweed ecosystems can help recover biodiversity. Seaweed ecosystem restoration can also improve nutrient cycling and overall ecosystem resilience to climate stressors.
Restoration of seaweed ecosystems is currently expensive, with costs varying widely depending on the method used. In kelp forests, chemical or manual urchin removal, which reduces grazing pressure, may cost between US$1,700/ha and US$76,000/ha in 2023 dollars, while most other approaches exceed US$590,000/ha.
It’s also unclear whether seaweed restoration efforts could scale enough to have a globally meaningful impact on GHG emissions. Using estimates from intact subtidal brown seaweed ecosystems, which are among the most productive and represent a likely upper limit on the effectiveness of seaweed restoration as a whole, restoration might remove 2.3 tCO₂‑eq
/ha/yr. At this rate, over 40 Mha would need to be restored to exceed 0.1 GtCO₂‑eq/yr.
However, most restoration projects are under 0.1 ha. For kelp forests, only roughly 2% (19,000 ha) have been restored out of the Kelp Forest Challenge’s target of 1 million ha by 2040, suggesting that this practice may not be scalable currently.
The effectiveness of restoration can also be offset by the life-cycle emissions of products required to re-establish some seaweed ecosystems. For example, emissions from the production of cement blocks needed to afforest some seaweed habitats have been estimated to potentially delay carbon removal benefits for 5–13 years in some systems.
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Eger, A. M., Vergés, A., Choi, C. G., Christie, H., Coleman, M. A., Fagerli, C. W., Fujita, D., Hasegawa, M., Kim, J. H., Mayer-Pinto, M., Reed, D. C., Steinberg, P. D., & Marzinelli, E. M.(2020). Financial and institutional support are important for large-scale kelp forest restoration. Frontiers in Marine Science, 7, 535277. Link to source: https://doi.org/10.3389/fmars.2020.535277
Eger, A. M., Marzinelli, E. M., Christie, H., Fagerli, C. W., Fujita, D., Gonzalez, A. P., Johnson, C., Ling, S. D., Mayer-Pinto, M., Norderhaug, K. M., Pérez-Matus, A., Reed, D. C., Sala, E., Steinberg, P. D., Wernberg, T., Wilson, S., & Vergés, A. (2022). Global kelp forest restoration: Past lessons, present status, and future directions. Biological Reviews, 97(4), 1449-1475. Link to source: https://doi.org/10.1111/brv.12850
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Seaweed ecosystem protection is the long-term protection from degradation of wild subtidal brown and red seaweed ecosystems. Seaweeds, also called macroalgae, are photosynthetic marine organisms that absorb CO₂ from the water and convert it into biomass. This can lower surface-water CO₂ concentrations, allowing additional CO₂ from the atmosphere to be dissolved in the ocean. Some of the fixed carbon can be sequestered through export to the deep sea or burial in the seafloor, while a portion may persist in forms that resist degradation even at the ocean surface.
Protecting seaweed ecosystems can reduce a range of human impacts (wild harvesting, coastal development, overgrazing, and poor water quality) and improve resilience to other stressors (warming), which helps preserve carbon removal by the seaweed and avoid CO₂ emissions from biomass losses.
This solution focuses on legal mechanisms of protection through the establishment of Marine Protected Areas (MPAs), which are managed with the primary goal of conserving nature. This solution does not include cultivated seaweed (see Deploy Seaweed Farming for Food).
Seaweeds are diverse marine photosynthetic organisms composed of three groups: brown (Phaeophyceae), green (Chlorophyta), and red algae (Rhodophyta). They can form ecosystems, such as kelp forests, and contribute to other marine ecosystems by providing habitat and food. Seaweeds are distinguished from other algae, such as phytoplankton, based on their larger size and because most are attached to substrate rather than free-floating. Seaweeds cover an estimated 600 Mha of the ocean (Duarte et al., 2022), an area that is an order of magnitude greater than the area associated with coastal wetlands (~55 Mha, see Protect Coastal Wetlands).
This solution focuses on wild subtidal (always submerged) brown and red seaweed ecosystems, which together account for over 75% of global seaweed extent (Duarte et al., 2022) (Figure 1). We do not include green seaweeds due to their smaller extent and data limitations. We also do not include seaweeds that occur in intertidal zones, as free-floating colonies (e.g., some species of Sargassum) or are cultivated due to data limitations or coverage in other Explorer solutions (e.g., Deploy Seaweed Farming for Food).
Seaweed ecosystems exhibit high net primary productivity (NPP) rates, comparable to those of terrestrial forests (Filbee-Dexter, 2020). Unlike many terrestrial ecosystems, however, nearly all carbon storage in seaweed ecosystems occurs as above-ground biomass, since seaweeds lack below-ground roots. A smaller amount can be buried on site in sediment (Krause-Jensen and Duarte, 2016). Most long-term carbon storage attributable to seaweeds occurs largely outside of seaweed ecosystems, through the export of carbon in dissolved and suspended forms (Figure 2). Some of this carbon reaches the deep sea, where it can persist for more than 100 years (Krause-Jensen and Duarte, 2016; Krause-Jensen et al., 2018; Ortega et al., 2019). Roughly 11.4% (25th quartile, 6.0%; 75th quartile, 13.7%) of NPP from global seaweed ecosystems is estimated to contribute to long-term carbon storage in the deep sea, equivalent to as much as 0.62 Gt CO₂‑eq/yr
(173 Tg C/yr, Krause-Jensen and Duarte, 2016). While uncertain and requiring more research, recent modelling efforts support these estimates, suggesting that more than 12.5% of NPP may be removed on 100-yr timescales (Filbee-Dexter et al., 2024).
Seaweed ecosystems face growing threats from a range of climate change impacts (Harley et al., 2012), such as increasing sea surface temperatures, marine heat waves, ocean acidification, and extreme storm events, as well as local drivers, such as overfishing, overgrazing, pollution, disease outbreaks, invasive species, and bottom fishing (Filbee-Dexter et al., 2024; Corrigan et al., 2025; Hanley et al., 2024). For instance, overfishing can deplete top predators in ecosystems, leading to increases in herbivores, such as sea urchins, that overgraze seaweed (Steneck et al., 2002).
In this solution, we calculate how legal protection of seaweed ecosystems via MPAs can reduce CO₂
emissions and preserve carbon removal through avoided ecosystem loss. In addition to preventing direct losses from impacts such as wild harvest, MPAs can help restore predator populations that keep herbivores in balance. For instance, many MPAs include no-take zones that allow predatory fish populations to recover, thereby lessening overgrazing impacts over time. MPAs can also increase the resilience of seaweed ecosystems against climate change stressors, such as marine heat waves (Ortiz-Villa et al., 2025; Kumagai et al., 2024). While some seaweed can release methane, offsetting CO₂
removal (Roth et al., 2023), we exclude this process from our analysis due to existing data limitations. We also do not consider nitrous oxide, though protection might provide additional climate benefits because enhanced nitrous oxide production has been tied to nutrient-polluted seaweed systems (Wong et al., 2021).
We present estimates of climate impact as likely upper bounds under several key assumptions (see Appendix and Caveats), which can be improved upon as more research unfolds. We consider subtidal brown and red seaweed to be protected if they are within designated MPAs based on global datasets from UNEP-WCMC and IUCN (2024). Importantly, protection can help reduce – but will not eliminate – ecosystem loss in MPAs relative to unprotected areas (see Effectiveness).
Figure 1. Seaweed ecosystem types considered in this solution (left to right): subtidal brown (central California, USA) and subtidal red (Atlantic coast of Spain)
Figure 2. Overview of a seaweed ecosystem, showing carbon fluxes into and out of the ecosystem.
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United Nations Environment Programme World Conservation Monitoring Centre (UNEP WCMC), & International Union for Conservation of Nature. (2024). Protected planet: The world database on protected areas (WDPA) and world database on other effective area-based conservation measures (WD-OECM) [Data set]. Retrieved April 2024, from Link to source: https://www.protectedplanet.net
United Nations Environment Programme (UNEP) (2023). Into the blue: Securing a sustainable future for kelp forests. United Nations Environment Programme. Link to source: https://wedocs.unep.org/handle/20.500.11822/42331
Waldron, A., Adams, V., Allan, J., Arnell, A., Asner, G., Atkinson, S., Baccini, A., Baillie, J., Balmford, A., & Austin Beau, J. (2020). Protecting 30% of the planet for nature: Costs, benefits and economic implications. Link to source: https://pure.iiasa.ac.at/id/eprint/16560/1/Waldron_Report_FINAL_sml.pdf
Wong, W. W., Greening, C., Shelley, G., Lappan, R., Leung, P. M., Kessler, A., Winfrey, B., Poh, S. C. & Cook, P. (2021). Effects of drift algae accumulation and nitrate loading on nitrogen cycling in a eutrophic coastal sediment. Science of the Total Environment 790, 147749. Link to source: https://doi.org/10.1016/j.scitotenv.2021.147749
Christina Richardson, Ph.D.
Ruthie Burrows, Ph.D.
Avery Driscoll, Ph.D.
James Gerber, Ph.D.
Daniel Jasper
Alex Sweeney
Aiyana Bodi
Avery Driscoll, Ph.D.
Christina Swanson, Ph.D.
Paul C. West, Ph.D.
The globally weighted average effectiveness of seaweed ecosystem protection is 0.32 tCO₂‑eq
/ha/yr. Protecting 1 ha of seaweed ecosystem avoids emissions of 0.043–0.13 tCO₂‑eq
/ha/yr while also sequestering an additional 0.083–0.43 tCO₂‑eq
/ha/yr, with effectiveness higher in subtidal brown than subtidal red seaweed ecosystems (100-yr GWP; Table 1; Appendix).
We estimated effectiveness as the avoided emissions and retained carbon sequestration capacity attributable to the reduction in seaweed ecosystem loss conferred by protection, as detailed in Equation 1. First, we calculated the difference between the rate of seaweed ecosystem loss outside and inside MPAs (Seaweed lossbaseline). We assumed a reduction in loss of 53% (Reduction in loss), which is based on estimates for a range of ecosystems in MPAs (Rodríguez-Rodríguez and Martínez-Vega, 2022). Importantly, this number is highly uncertain and likely to be highly variable, too.
Next, we multiplied this product by the sum of the avoided CO₂
emissions associated with the one-time loss of all above ground biomass carbon in 1 ha of seaweed ecosystem each year over 30 years (Carbonavoided emissions) and the amount of carbon sequestered via long-term storage (on-site or off-site) in 1 ha of protected seaweed ecosystem each year over 30 years (Carbonsequestration).
We based these rates on original analysis of a subset of studies conducted over, at least, 20 years, collated from Krumhansl et al. (2016), that show a median loss rate of 1.2% per year for kelp forests. Due to data limitations, we applied this loss rate to subtidal red seaweed ecosystems as well, but recognize that loss rates are likely to be highly variable. We did this calculation separately for red and brown seaweed ecosystems due to their distinct biomass densities and sequestration capacities, and then averaged the results with accommodations for their relative global areas.
Equation 1.
Table 1. Effectiveness of seaweed ecosystem protection in avoiding emissions and sequestering carbon.
Unit: tCO₂‑eq /ha/yr, 100-year basis
| Avoided emissions, estimate | 0.13 |
| Sequestration | 0.43 |
| Total effectiveness, estimate | 0.56 |
| Total effectiveness, 25th percentile | 0.21 |
| Total effectiveness, 75th percentile | 0.91 |
Unit: tCO₂‑eq /ha/yr, 100-year basis
| Avoided emissions, estimate | 0.043 |
| Sequestration | 0.083 |
| Total effectiveness, estimate | 0.13 |
| Total effectiveness, 25th percentile | 0.034 |
| Total effectiveness, 75th percentile | 0.22 |
Unit: tCO₂‑eq /ha/yr, 100-year basis
| Avoided emissions, estimate | 0.080 |
| Sequestration | 0.24 |
| Total effectiveness, estimate | 0.32 |
| Total effectiveness, 25th percentile | 0.11 |
| Total effectiveness, 75th percentile | 0.52 |
We estimate that seaweed ecosystem protection might save approximately US$72/tCO₂‑eq , but emphasize that these estimates are highly uncertain due to existing data limitations. This is based on protection costs of roughly US$14/ha/yr and revenue of US$43/ha/yr compared with the baseline (Table 2). The costs of seaweed ecosystem protection also include up-front one-time expenditures of US$208 (surveys, administrative setup, legal fees, etc.), estimated from McCrea-Strub et al. (2011). However, data related to the costs of seaweed ecosystem protection are limited, and these estimates are uncertain. For consistency across solutions, we did not include revenue associated with other ecosystem services.
We estimated costs of MPA maintenance at US$14/ha/yr based on data from existing MPAs, though only 16% of MPAs surveyed reported their current funding was sufficient (Balmford et al., 2004). Maintenance is critical for seaweed ecosystems, especially those prone to overgrazing. Tourism revenues directly attributable to protection were estimated to be $43/ha/yr (Waldron et al., 2020) based on estimates for all MPAs (and PAs) and not including downstream revenues. However, estimates of tourism revenues are highly uncertain for seaweed ecosystems. In some seaweed ecosystems, such as kelp forests, tourism is likely a real revenue generator through diving or other recreational activities, but the financial contribution is generally unclear and poorly documented across all seaweed ecosystems.
Table 2. Cost per unit of climate impact. Negative values indicate cost savings.
Unit: 2023 US$/tCO₂‑eq , 100-yr basis
| Estimate | -72 |
A learning curve is defined here as falling costs with increased adoption. The costs of seaweed ecosystem protection do not fall with increasing adoption, so there is no learning curve for this solution.
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.
Protect Seaweed Ecosystems 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.
Additionality is an important caveat for ecosystem protection. In our analysis, we used baseline rates of seaweed ecosystem loss to calculate the effectiveness of protection, which are highly uncertain and understudied. This assumes that seaweed ecosystems would continue to be lost at these rates in the absence of protection and thus that protection provides additional carbon benefits from the ecosystems whose loss is avoided.
Importantly, effective protection depends on adequate funding and management. Poorly managed MPAs can fail to prevent key stressors, such as urchin overgrazing, from increasing and undermine the viability of seaweed ecosystems. Similar dynamics have been documented in kelp restoration efforts, where inadequate management has led to overgrazing and project failure (Eger et al., 2022).
The permanence of ecosystem carbon benefits is another key caveat. While seaweed ecosystems are expanding or expected to expand with climate change, in some regions many will contract (Corrigan et al., 2025). Protection may increase resilience to some climate change stressors, but it will not fully prevent ecosystem loss in many regions. Additionally, because seaweed ecosystems sequester carbon both on-site and off-site, the effectiveness of protection partly depends on downstream activities. For instance, carbon at the seafloor is threatened by disturbances such as bottom fishing and mining (see Protect Seafloors). Protection of seaweed ecosystems does not prevent loss of downstream stored carbon, some of which is contributed by seaweed ecosystems (Ortega et al., 2019). Additionally, seaweed biomass extent can change dramatically from year to year, which could result in substantial variability in carbon removal rates despite protection.
Another caveat in this solution lies in our assumptions about carbon dynamics at the ocean surface. We assume that seaweed NPP results in an equivalent removal of CO₂ from the atmosphere. In reality, this influx may not be fully efficient (Hurd et al., 2025). In some regions of the ocean, water carrying a CO₂ -deficit from seaweed photosynthesis might be subducted before it reaches equilibrium with the atmosphere, which would reduce the atmospheric removal attributed to seaweed productivity in our calculations.
In our analysis, avoided emissions are calculated under the assumption that destruction of a seaweed ecosystem results in the loss of all biomass carbon This likely overestimates near-term emissions, as some carbon may remain in the ocean for long periods. However, this fraction is expected to be small given that an estimated 6.0–13.7% (average: 11.4%) of NPP is thought to be stored long term (Krause-Jensen and Duarte, 2016).
Finally, the relative fraction of NPP removed and durably stored (>100 years) is also uncertain (Pessarrodona et al., 2023). Despite this uncertainty, our use of 11.4% is supported by recent modeling of particulate carbon fluxes that suggest ~12.5% of NPP could be sequestered on a 100-year timescale (based on 44 Tg C of particulate organic carbon export to 1,000 m, where carbon is less likely to return to the atmosphere within a century, and ~353 Tg C as NPP; Filbee-Dexter et al., 2024), but requires more research.
A total of 78.8 Mha of seaweed ecosystems are currently within MPAs (Table 3). Cumulatively, roughly 18% of seaweed ecosystems are under some form of protection, with 4% located in strictly protected MPAs, 6% in nonstrict MPAs, and 8% in other IUCN protection categories. Subtidal brown and red seaweed ecosystems have similar rates of existing protection in all protection categories (Figure 2).
Table 3. Current (circa 2023) extent of seaweed ecosystems under legal protection. “Strict protection” includes land within IUCN categories I–II Marine Protected Areas (MPAs). “Nonstrict -protection” includes land within IUCN Categories III–VI MPAs. “Other” includes land within all remaining IUCN MPA categories. Values may not sum to global totals due to rounding.
Unit: Mha protected
| Strict protection | 8.43 |
| Nonstrict protection | 11.40 |
| Other | 15.50 |
| Total | 35.3 |
Unit: Mha protected
| Strict protection | 9.28 |
| Nonstrict protection | 16.30 |
| Other | 18.00 |
| Total | 43.50 |
Unit: Mha protected
| Strict protection | 17.70 |
| Nonstrict protection | 27.60 |
| Other | 33.40 |
| Total | 78.80 |
We calculated the rate of MPA expansion in seaweed ecosystems based on recorded year of establishment (UNEP-WCMC, & IUCN, 2024). Protection expanded by a median of 0.74 Mha/yr in subtidal brown seaweed ecosystems and 0.97 Mha/yr in subtidal red seaweed ecosystems (Table 4; Figure 2a). The global average rate of expansion was roughly 2.1 Mha/yr, with a median of 1.7 Mha/yr. The adoption trend for subtidal brown and red seaweed was relatively similar, with both expanding 0.46–0.55%/yr, on average (median of 0.39–0.40%/yr) (Figure 2b).
Table 4. 2000–2024 adoption trend. Global totals reflect independent statistics, not sums of subtidal brown and red values.
Unit: Mha/yr
| 25th percentile | 0.40 |
| Median (50th percentile) | 0.74 |
| Mean | 1.01 |
| 75th percentile | 1.31 |
Unit: Mha/yr
| 25th percentile | 0.62 |
| Median (50th percentile) | 0.97 |
| Mean | 1.12 |
| 75th percentile | 1.45 |
Unit: Mha/yr
| 25th percentile | 1.02 |
| Median (50th percentile) | 1.71 |
| Mean | 2.13 |
| 75th percentile | 2.76 |
Figure 3. Trend in seaweed ecosystem protection (2000-2024) in terms of (A) total hectares protected and (B) the percent of the current adoption ceiling that is currently protected. These values reflect only the area located within Marine Protected Areas. Unit: million hectares protected and percent protected relative to the adoption ceiling (%).
We estimated that approximately 430 Mha of wild seaweed ecosystems are available for protection (Table 6). Subtidal red seaweeds compose ~240 Mha, with subtidal brown seaweeds occupying the remaining ~190 Mha. These adoption areas do not include other types of seaweed habitats/ecosystems, such as those found in the intertidal zone, rhodolith beds, Halimeda bioherms, coral reefs, and pelagic, free-floating seaweed, which could account for an additional ~150 Mha (Duarte et al., 2022). These adoption areas are highly uncertain due to data limitations and are also likely to shift with climate change.
Table 5. Adoption ceiling: upper limit for the adoption of legal protection of seaweed ecosystems.
Unit: Mha
| Estimate | 189.6 |
Unit: Mha
| Estimate | 243.0 |
Unit: Mha
| Estimate | 432.6 |
We defined the lower end of the achievable range for seaweed ecosystem protection (across all IUCN categories) as 50% of the adoption ceiling and the upper end of the achievable range as 70% of the adoption ceiling. These adoption levels are ambitious relative to existing levels of protection (~18%), but align with targets to protect 30% of ecosystems by 2030 (Eger et al., 2024) and serve as an optimistic benchmark for the 30-year time horizon considered in our analysis. Several countries already protect more than 30% of subtidal brown seaweed ecosystems, such as kelp forests (Kelp Forest Alliance, 2024). For example, the United Kingdom, Japan, China, and France protect over 41%, 68%, 68%, and 47% of their kelp beds, respectively.
Table 6: Range of achievable adoption levels for seaweed ecosystems.
Unit: Mha
| Current adoption | 78.8 |
| Achievable – low | 216.3 |
| Achievable – high | 302.9 |
| Adoption ceiling | 432.6 |
We estimated that MPAs currently avoid emissions of 0.03 GtCO₂‑eq/yr in seaweed ecosystems, with potential impacts of 0.14 GtCO₂‑eq/yr at the adoption ceiling (Table 7). Achievable levels of seaweed ecosystem protection could safeguard 0.07 to 0.10 GtCO₂‑eq/yr by reducing emissions from biomass loss and retaining sequestration fluxes (Table 7). However, these estimates are highly uncertain and will benefit from more research (see Caveats).
Limited data exist on the potential climate impacts of seaweed ecosystem protection for comparison. However, a rough estimate of the benefits of conservation, restoration, and afforestation interventions of seaweeds suggests carbon benefits of at least 0.04 GtCO₂‑eq/yr (Pessarrodona et al., 2023). Other estimates suggest that total carbon sequestration in seaweed ecosystems could be on the order of 0.22–0.98 GtCO₂‑eq/yr (Krause-Jensen and Duarte, 2016). This is higher than our estimates because we account only for the carbon benefits of protection in seaweed ecosystems at risk of loss.
Table 7. Climate impact at different levels of adoption. Values may not sum to global totals due to rounding.
Unit: GtCO₂‑eq/yr, 100-year basis
| Current adoption | 0.02 |
| Achievable – low | 0.05 |
| Achievable – high | 0.07 |
| Adoption ceiling | 0.11 |
Unit: GtCO₂‑eq/yr, 100-year basis
| Current adoption | 0.01 |
| Achievable – low | 0.02 |
| Achievable – high | 0.02 |
| Adoption ceiling | 0.03 |
Unit: GtCO₂‑eq/yr, 100-year basis
| Current adoption | 0.03 |
| Achievable – low | 0.07 |
| Achievable – high | 0.10 |
| Adoption ceiling | 0.14 |
Seaweeds can provide coastal resilience to the impacts of storms by lowering wave heights before they reach shorelines (Corrigan et al., 2025; Cotas et al., 2023). The magnitude of this benefit can vary based on the species and location of seaweed, and some evidence suggests that severe storms can harm seaweed habitats (Earp et al., 2024). Evidence suggests that kelp forests can attenuate wave heights locally, especially in the summer at peak kelp growth, but protection varies at larger spatial scales (Elsmore et al., 2024; Lindhart et al., 2024). Emerging research has found that protected seaweed ecosystems show more resilience to marine heat waves than unprotected areas (Kumagai et al., 2024). During heat waves, protected ecosystems maintain a habitat for species like sea urchins which support a healthier kelp ecosystem by predating other species who may eat and degrade kelp ecosystems (Kumagai et al., 2024; Bauer et al., 2025).
Seaweeds support species that are important for tourism and fishing (Cuba et al., 2022; Eger et al., 2023). Many species that are supported by seaweeds have high economic value for fishing, such as crabs, lobsters, and abalones (Corrigan et al., 2025). For example, Eger et al. (2023) estimated that 1 ha of kelp forest where about 900 kg of fish biomass is harvested could yield about US$29,900 a year. The same study estimated that the global value of kelp forests that support fisheries is about US$465–562 billion (Eger et al., 2023). Seaweed habitats can also be tourist destinations for snorkeling and diving (UNEP, 2023), providing income-earning opportunities for nearby communities.
The contribution of seaweeds to fisheries production can play a role in global food security (Cottier-Cook et al., 2023, Eger et al., 2023). Additionally, seaweeds are an essential part of many diets, especially in East Asia (FAO, 2024). Because seaweeds are a culturally important food in many geographies, protecting seaweeds can play an important role in equitably improving global food security (FAO, 2024).
For some cultures, seaweeds and their habitats shape shared identities and livelihoods (Cotas et al., 2023). For example, seaweeds are a source of traditional foods, medicines, art, and knowledge for many coastal communities and Indigenous peoples (Thurstan et al., 2018). Protecting seaweeds can preserve the cultural identities, practices, and knowledge of Indigenous communities that are often vulnerable (Corrigan et al,, 2025).
Seaweeds support biodiversity by providing habitat for a variety of marine species (Best et al., 2014; Cuba et al., 2022; Gibbons and Quijón, 2023; Tano et al., 2016). Literature reviews of the ecosystem services of seaweeds find that they contribute to increases in biodiversity (Gibbons and Quijón, 2023). Seaweeds can provide habitat and refuge from large predators (Best et al., 2014; Gibbons and Quijón, 2023). Invertebrates, detritivores, and other small species found in seaweed forests are essential food sources for other marine species (Cuba et al., 2016; Tano et al., 2016).
Seaweeds improve water quality by supporting nutrient cycling and reducing pollutants (Cotas et al., 2023; Heckwolf et al., 2021). Evidence suggests that seaweeds can reduce eutrophication by filtering excess nutrients from the water (Corrigan et al., 2025; Heckwolf et al., 2021; Gao et al., 2022).
Leakage, in which protecting one ecosystem results in the degradation of another, could offset the climate impact of seaweed ecosystem protection. For instance, restricting wild harvesting through the establishment of an MPA could shift pressure to other unprotected areas. Another key risk is weakly enforced or poorly managed MPAs. This is a real concern with existing MPAs due to a lack of funding, and can result in low protection effectiveness. Finally, climate change stressors, such as ocean warming and marine heat waves, are a major risk to permanence because they could lead to widespread mortality, even in protected areas.
Intact and healthy seaweed ecosystems can enhance fish stocks, biodiversity, and habitat quality, which benefits all connected coastal and marine ecosystems.
Protecting seaweed ecosystems can help ensure the underlying areas of the seafloor remain intact.
Protection of seaweed ecosystems could potentially reduce the adoption of offshore wind in some regions.
ha of seaweed ecosystem protected
CO₂
Seaweed ecosystems can release methane, which could reduce the climate benefits of protection estimated in this solution. While data are scarce , a recent study suggests that methane emissions could offset 28–35% of the carbon sink capacity in some seaweed ecosystems (Roth et al., 2023) if they escape to the atmosphere, which may be unlikely if methane production occurs at depth in sediments (Pessarrodona et al., 2023).
Consensus of effectiveness at reducing emissions and maintaining carbon removal: Mixed
There is mixed scientific consensus that protection prevents the degradation of seaweed ecosystems, but high consensus that degradation leads to losses in biomass carbon stocks and sequestration capacity. Seaweed ecosystems can be degraded by diverse stressors that directly or indirectly affect biomass stocks. Management actions, such as establishment of MPAs, can help prevent both direct and indirect habitat loss and thereby maintain the carbon removal capacity of seaweed ecosystems with relatively high certainty against stressors such as wild harvesting, coastal development, overgrazing, and poor water quality (Pessarrodona et al., 2023). However, some stressors, such as marine heat waves and ocean warming, are less effectively addressed by protection alone (Filbee-Dexter et al., 2024). Benefits are still expected in some systems because MPAs can enhance resilience and recovery by reducing co-occurring stressors common that contribute to seaweed ecosystem degradation (Krumhansl et al., 2016; Ortiz-Villa et al., 2025). Moreover, MPAs, even when established in areas with addressable stressors, are typically not fully effective. Here, we applied a protection effectiveness of 53%, based on aggregated estimates from MPAs beyond seaweed ecosystems (Rodríguez-Rodríguez and Martínez-Vega, 2022). If the effectiveness of protection is lower (higher), climate impacts could likewise be lower (higher).
There is high scientific consensus that degradation of seaweed ecosystems leads to losses in biomass carbon stocks and sequestration capacity. While direct estimates of CO₂ emissions from biomass are limited, degradation has been shown to remove biomass carbon and reduce sequestration. For instance, drivers of habitat loss and degradation, such as overharvesting (Steen et al., 2016; González-Roca et al., 2021), overgrazing (Akaike & Mizuta, 2024), and poor water quality (Filbee-Dexter & Wernberg, 2020), reduce standing biomass and therefore associated carbon export from seaweed ecosystems (Pessarrodona et al., 2023).
The carbon sink capacity of seaweed ecosystems, such as kelp forests, is also expected to decline with climate change stressors such as warming, which can increase rates of decomposition 9–42% (Filbee-Dexter et al., 2022) and drive habitat loss, both of which reduce the likelihood that carbon makes its way to the deep sea for long-term storage. Off the coast of Australia, over 140,000 ha of subtidal brown seaweed forests have already been lost to warming over two decades, representing a decline of 2–4% of regional seaweed biomass carbon stocks and sequestration capacity (Filbee-Dexter & Wernberg, 2020).
The results presented in this assessment synthesize findings from 5 global datasets. We recognize that geographic bias in the information underlying global data products creates bias, and hope this work inspires research and data sharing on this topic in underrepresented regions and on understudied aspects of these ecosystems.
This analysis quantifies emissions that can be avoided by protecting seaweed ecosystems via the establishment of Marine Protected Areas (MPAs). We leveraged two global seaweed distribution maps alongside a shapefile of MPAs, available data on rates of avoided ecosystem loss attributable to MPA establishment, and global data on biomass carbon stores and carbon sequestration rates to calculate climate impacts. This appendix describes the source data products and how they were integrated.
Seaweed Ecosystem Extent
We relied on the global maps of seaweed extent developed by Duarte et al. (2022), which classify subtidal brown and red seaweeds (among others). We used the “LT2 Brown Algae Benthic” raster to calculate subtidal brown seaweed extent and the “LT2 Red Algae Benthic” raster to calculate subtidal red seaweed extent. We did not consider red seaweed in subtidal brown-dominant environments, such as kelp forests, due to existing limitations with the global maps.
Protected Seaweed Ecosystem Areas
We identified protected seaweed ecosystem areas using the World Database on Protected Areas (WDPA, 2024), which contains boundaries for each MPA and additional information, including the establishment year and IUCN management category (Ia to VI, not applicable, not reported, or not assigned). In this analysis, we considered all protection categories). While some MPA categories likely allow for wild harvest, which can be unsustainably conducted, wild seaweed harvest is currently estimated at 1.3 Mt/yr (wet weight) (FAO, 2024), which represents a relatively small portion of the global loss rate used (<0.2%/yr). We converted the MPA boundary data to a raster and used them to calculate the seaweed area within MPA boundaries for each seaweed type analyzed (subtidal brown and red) and each MPA category. To evaluate trends in adoption over time, we also aggregated protected areas by establishment year as reported in the WDPA.
Avoided Seaweed Ecosystem Conversion
We compiled baseline estimates of seaweed ecosystem loss (%/yr) from existing literature and used them in conjunction with an estimate of reductions in loss associated with protection of 53% (derived from Rodríguez-Rodríguez and Martínez-Vega, 2022) to calculate the rate of avoidable macroalgae loss (Seaweed lossavoidable). Seaweed ecosystem loss rates were based on the original analysis of data aggregated from Krumhansl et al. (2016) for studies over 20 years long (Seaweed lossbaseline; median loss rate of 1.2%/yr).
Equation A1.
We then used the avoidable seaweed loss rates to calculate avoided CO₂ emissions and additional carbon sequestration for each adoption unit. Specifically, we estimated the carbon benefits of avoided seaweed ecosystem loss by multiplying avoided seaweed ecosystem loss by avoided CO₂ emissions (Equation A2) and by applying carbon sequestration rates over 30 years (Equation A3) for each seaweed type.
We estimated avoided CO₂ emissions by assuming a one-time release of all aboveground biomass carbon upon loss. We derived our estimates of retained carbon sequestration from global databases on NPP for each seaweed type from Duarte et al. (2022) and a global estimate of NPP-derived sequestration (11.4%) from NPP based on Krause-Jensen and Duarte (2016).
Equation A2.
Equation A3.
We then estimated effectiveness (Equation A4) as the avoided CO₂ emissions and retained carbon sequestration capacity attributable to the reduction in seaweed ecosystem loss conferred by protection estimated in Equations A1–3.
Equation A4.
Forest restoration is the process of returning previously forested land to a forested state. As forests regrow, they remove carbon from the atmosphere and sequester it in biomass.
We define forest restoration as planting new trees or allowing trees to naturally regrow on previously forested land that has been cleared. Through photosynthesis, forests take carbon from the atmosphere and store it in biomass. On net, forests currently take up an estimated 11.4–14.7 Gt CO₂‑eq/yr (Friedlingstein et al., 2023; Gibbs et al., 2025; Pan et al., 2024), equal to approximately 19–25% of total global anthropogenic GHG emissions (Dhakal et al., 2022). Restoring forests increases the size of the forest carbon sink, sequestering additional CO₂.
As commonly defined, restoration ranges from improving management of existing ecosystems, to re-establishing cleared ecosystems, to maintaining the health of functional ecosystems. Forest restoration includes activities such as exclusion of non-native grazing animals from a regenerating site, weed management, assisted seed dispersal, controlled burning, stand thinning, direct seeding, soil amendment, tree planting, and modification of topography or hydrology and other activities (Chazdon et al., 2024; Gann et al., 2022; Kübler & Günter 2024). While acknowledging that all restoration occurs along a spectrum of intervention intensity, we report effectiveness, cost, and adoption data for “low intensity” and “high intensity” restoration separately, with “low intensity” restoration including all interventions up to, but not including, tree planting, and “high intensity” restoration referring to direct seeding or seedling planting. To account for variability in carbon sequestration rates and area available for forest restoration, this analysis also evaluates forest restoration in boreal, temperate, subtropical, and tropical regions separately where possible.
Our definition of forest restoration is more limited than that used by many other sources. First, we only include reforestation of previously forested land with an element of direct human intervention, and therefore exclude entirely passive tree regrowth on abandoned land (i.e., unassisted natural regeneration) and afforestation of native grasslands and savannas. We also exclude areas currently used for crop production. To avoid double counting, we also do not include activities covered in other Project Drawdown solutions, including increasing carbon stocks in existing forests and establishing timber plantations, agroforestry, or silvopasture (see Improve Forest Management, Deploy Biomass Crops on Degraded Land, Deploy Agroforestry, and Deploy Silvopasture, respectively). Restoration of mangroves and forests on peat soils is also excluded, as this is covered in the Restore Coastal Wetlands and Restore Peatlands solutions. Because the scope of this solution is narrower than that of many other studies, the estimated impacts are correspondingly lower as well.
Intact and regenerating forests take up carbon, but human clearing of forests for logging, agriculture, and other activities emits carbon. Humans clear an estimated 15.5 Mha of forests annually, emitting ~7.4 Gt CO₂‑eq/yr (2001–2024; Harris et al., 2021; Gibbs et al., 2025; Sims et al., 2025). Protecting existing forests reduces emissions from deforestation (see Protect Forests) and is an essential complement to forest restoration.
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Avery Driscoll, Ph.D.
Ruthie Burrows, Ph.D.
James Gerber, Ph.D.
Daniel Jasper
Alex Sweeney
James Gerber, Ph.D.
Megan Matthews, Ph.D.
Paul C. West, Ph.D.
We estimated that forest restoration can sequester 5.86–18.19 t CO₂‑eq /ha/yr (Table 1), depending on the climate zone and type of intervention, as growing trees take up carbon through photosynthesis and store it in above- and below-ground biomass. Sequestration rates are highly variable globally; much of this variability is driven by climate, soil properties, forest type, and the type of restoration.
For this solution, we used modeled carbon sequestration rates from natural regeneration to represent low-intensity restoration (Robinson et al., 2025) and modeled carbon sequestration rates from plantation forests to represent high-intensity carbon restoration, which we define as initiatives that include tree planting (Bukoski et al., 2022; Busch et al., 2024). We calculated carbon sequestration rates at the climate zone level (boreal, temperate, subtropical, and tropical) across the potential extent for each reforestation type.
Generally, high-intensity restoration has higher sequestration rates (median values 12.02–18.19 t CO₂‑eq /ha/yr) than low-intensity restoration (median values 5.86–17.06 t CO₂‑eq /ha/yr). Median effectiveness is also higher in tropical areas, where forest growth often continues year-round, than it is in other climate zones. These estimates reflect average sequestration rates over the first 30 years of forest growth. Carbon sequestration rates are also influenced by non-climatic factors. For example, higher tree species diversity is often associated with higher forest carbon storage and uptake (Bialic-Murphy et al., 2024; Poorter et al., 2015; van der Sande et al., 2017).
Table 1. Effectiveness of forest restoration at sequestering carbon.
Unit: t CO₂‑eq /ha/yr, 100-yr basis
| Boreal | 5.86 |
| Temperate | 11.49 |
| Subtropical | 11.53 |
| Tropical | 17.06 |
Unit: t CO₂‑eq /ha/yr, 100-yr basis
| Boreal | 14.57 |
| Temperate | 12.74 |
| Subtropical | 12.02 |
| Tropical | 18.19 |
We estimated the median cost of low-intensity forest restoration at US$23/t CO₂‑eq (2023 US$) and the median cost of high-intensity forest restoration at US$83/t CO₂‑eq (Table 2). The value given in the dashboard above is the average of the low- and high-intensity cost estimates (US$53/t CO₂‑eq).
On a per-hectare basis, the estimated cost of low-intensity restoration ranges from US$213/ha (25th percentile) to US$739/ha (75th percentile), with a median cost of US$304/ha. The estimated cost of high-intensity restoration ranges from US$811/ha (25th percentile) to US$1,914/ha (75th percentile), with a median of US$1,348/ha. We derived these estimates from compilations of global restoration project cost data by Verhoeven et al. (2024) and Busch et al. (2024), supplemented with estimates from five additional publications, representing a total of 50 unique projects.
Estimates of restoration costs remain very uncertain, as data are scarce, costs and revenues are highly variable across geographies and projects, and costs are nonlinear, tending to increase under higher adoption scenarios (Austin et al., 2020; Schimetka et al., 2024). Moreover, the success of a project at establishing new forests drives the cost per metric ton of CO₂‑eq , but such success rates are rarely reported alongside costs. Because of data limitations, we did not separate cost estimates into climate zones.
Our estimates do not account for any new revenues associated with forest restoration, such as carbon credits or provisioning of timber and non-timber forest products (Adams et al. 2016; Ager et al., 2017; Busch et al., 2024). They also do not account for the economic value of ecosystem services, such as increased biodiversity, improved water quality, local cooling, and reduced soil erosion, which have been estimated to outweigh the costs of forest restoration (De Groot et al., 2013).
Table 2. Cost per unit of climate impact.
Unit: 2023 US$/t CO₂‑eq , 100-yr basis
| Median | 23 |
Unit: 2023 US$/t CO₂‑eq , 100-yr basis
| Median | 83 |
We define a learning curve as falling costs with increased adoption. Reforestation has been practiced for many decades, and there is no evidence of a decrease in costs associated with increasing adoption. Therefore, there is no learning curve for this solution.
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.
Restore Forests is a DELAYED climate solution. It works more slowly than gradual or emergency brake solutions. Delayed solutions can be robust climate solutions, but it’s important to recognize that they may not realize their full potential for some time.
Barriers to effective forest restoration include challenges around governance, financing, technical capacity (including seed and seedling supply), labor availability, and site-specific knowledge for initial restoration and long-term management (Brumberg et al., 2024; Chazdon et al., 2016; Chazdon et al., 2021; Fargione et al., 2021; Kroeger et al., 2025). Additional research and monitoring are needed to identify locally relevant restoration strategies, reduce barriers, and evaluate the success of restoration projects (Crouzeilles et al., 2019).
Forest restoration also faces challenges around permanence and additionality. Carbon stored in vegetation and soils through forest restoration can be lost to climatic and environmental stressors like wildfire, drought, heat waves, pests, or disease. Young, regenerating forests can be particularly susceptible to these types of stressors. Restored forests are also at risk of clearing (e.g., Piffer et al., 2022), so forest restoration must be coupled with long-term, effective protections against clearing. Additionality refers to the degree to which carbon uptake associated with forest restoration would have occurred in the absence of a project, policy, or incentive. Evaluating additionality is challenging in the context of natural forest regeneration, some of which simply arises from land abandonment without any intervention.
Data on current adoption of forest restoration are very limited. While there are extensive compilations of restoration pledges, estimates of the actual area being restored are noncentralized, typically rely on self-reporting without validation, do not have global coverage, use inconsistent definitions, often include establishment of plantations and agroforestry, and rarely separate estimates by ecosystem. Satellite-based data on tree cover gain are occasionally used as a proxy for restoration, but these do not differentiate among restoration, establishment of timber plantations, regeneration in the absence of human intervention, and plantation regrowth after timber harvest (Reytar et al., 2024). Moreover, they can fail to capture actual restoration areas (Begliomini & Brancalion, 2024).
Due to these limitations, we do not provide an estimate of the global area currently under forest restoration. However, we did compile current restoration estimates from three databases: The Mongabay Reforestation Catalog, The Restoration Initiative, and The Restoration Barometer. These databases are subject to the limitations discussed above. Assuming that there is no overlap in projects reported across these databases, including projects with an agroforestry component, and including projects across all ecosystems, we found 40.6 Mha currently being restored. Under more conservative assumptions, including removing projects with an agroforestry component, removing projects from countries that are reported across multiple databases, and discounting estimates to account for restoration in other ecosystems, we estimated that 9.2 Mha are currently being restored. These estimates provide context, but should not be interpreted as representative of the global area under forest restoration.
Despite extensive data on restoration pledges, comprehensive data on the actual implementation of restoration efforts are very limited and not often temporally resolved. The available data are insufficient to calculate an adoption trend for this solution.
We estimated that there are 96.8 Mha available for forest restoration, with 19.4 Mha in boreal regions, 19.0 Mha in temperate regions, 3.5 Mha in the subtropics, and 54.8 Mha in the tropics (Table 3a–e). In this solution, we only included cleared areas that were previously forests in the calculation of the adoption ceiling. To calculate the adoption ceiling, we started with a recent, conservative map of potential forest restoration areas (Fesenmeyer et al., 2025), which we masked to exclude areas classified as other ecosystems in other solutions (peatlands, grasslands and savannahs, and coastal wetlands). We then used a map of the cost-effectiveness of natural regeneration versus plantation establishment (Busch et al., 2024) to remove areas more suitable for plantation establishment from this solution, and assigned them instead to the Deploy Biomass Crops on Degraded Land solution.
Estimates of the area available for forest restoration vary widely due to differing definitions, ranging from 195 Mha (Fesenmeyer et al., 2025) to 900 Mha (Bastin et al., 2019), for example. Using base maps of forest restoration potential from Griscom et al. (2017) and Walker et al. (2022) gave an estimated global adoption ceiling of 426–434 Mha, after applying the same data processing approach to exclude other ecosystems and plantations.
Because of the constrained scope of this solution, we find a smaller adoption ceiling relative to other studies, which often include plantation establishment, agroforestry, densification of existing forests, afforestation on grasslands, restoration of forests on peat soils, reforestation of croplands, and other activities sometimes classified as forest restoration. We leveraged the map from Fesenmeyer et al. (2025) for the estimates reported in Table 3 because its scope aligns most closely with our relatively narrow definition of forest restoration, is one of the most recent studies, includes a review of 89 other forest restoration maps, and incorporates safeguards against conflicts between restoration and biodiversity loss, water scarcity, albedo effects, and land use. However, we note that this estimate is lower than other published estimates of potential forest restoration area and that differences across studies are driven by subjective judgments on land suitability for restoration.
Table 3. Adoption ceiling.
Unit: ha available for restoration
| Estimate | 19,400,000 |
Unit: ha available for restoration
| Estimate | 19,000,000 |
Unit: ha available for restoration
| Estimate | 3,500,000 |
Unit: ha available for restoration
| Estimate | 54,800,000 |
Unit: ha available for restoration
| Estimate | 96,800,000 |
We assigned an arbitrary achievable range of 50–75% of the adoption ceiling, equal to 48.4–72.6 Mha of forest restoration (Table 4a–e). Much of the adoption potential is located in the tropics, which we estimated to contain 27.4 Mha under the Achievable – Low Scenario and 41.1 Mha under the Achievable – High Scenario. We estimated similar achievable ranges of forest restoration area in boreal and temperate regions (9.7–14.6 Mha and 9.5–14.3 Mha, respectively), and an additional 1.7–2.6 Mha in subtropical regions.
Additional research is needed to determine more realistic estimates of the achievable adoption range, particularly differentiated across different restoration activities. National commitments to restoration, as with studies on the potential restoration area, include many activities that are beyond the scope of this solution, such as plantation establishment, agroforestry, and densification. Because of the inconsistency in definitions, we were unable to rely on restoration commitments to quantify the adoption achievable range. For context, the Global Restoration Commitments database (Mariappan & Zumbado, 2024) reports that, under the Rio Conventions, countries have committed to increasing forestland by 122 Mha, with an additional 154 Mha of commitments to restoring or improving forestland. Similarly, 210.1 Mha of land have been pledged for restoration across all ecosystems under the Bonn Challenge (Mariappan & Zumbado, 2024).
Table 4. Range of achievable adoption levels.
Unit: ha
| Current adoption | NA |
| Achievable – low | 9,700,000 |
| Achievable – high | 14,600,000 |
| Adoption ceiling | 19,400,000 |
Unit: ha
| Current adoption | NA |
| Achievable – low | 9,500,000 |
| Achievable – high | 14,300,000 |
| Adoption ceiling | 19,000,000 |
Unit: ha
| Current adoption | NA |
| Achievable – low | 1,700,000 |
| Achievable – high | 2,600,000 |
| Adoption ceiling | 3,500,000 |
Unit: ha
| Current adoption | NA |
| Achievable – low | 27,400,000 |
| Achievable – high | 41,100,000 |
| Adoption ceiling | 54,800,000 |
Unit: ha
| Current adoption | NA |
| Achievable – low | 48,400,000 |
| Achievable – high | 72,600,000 |
| Adoption ceiling | 96,800,000 |
We estimated that forest restoration could sequester 0.718 Gt CO₂‑eq/yr at the low-achievable adoption scenario, 1.077 Gt CO₂‑eq/yr at the high-achievable adoption scenario, and 1.437 Gt CO₂‑eq/yr at the adoption ceiling (Table 5a–e). Nearly 70% of the total climate impacts under these scenarios occur in tropical regions, where much of the current investment in restoration is focused.
Our climate impact estimates are lower than existing literature estimates due to our more constrained definition of this solution. Existing estimates also vary widely. For example, Cook-Patton et al. (2020) estimated that fully implemented national forest restoration commitments as of 2020 would take up 5.9 Gt CO₂‑eq/yr, while the Intergovernmental Panel on Climate Change (IPCC) reported an economically feasible mitigation potential of 1.6 Gt CO₂‑eq/yr (Nabuurs et al., 2022), and Griscom et al. (2017) reported a technical mitigation potential of 10.1 Gt CO₂‑eq/yr. Recently, Wang et al. (2025) estimated an upper-end mitigation potential of 5.85 Gt CO₂‑eq/yr (including afforestation and plantation establishment), with current commitments across all of these activities projected to take up 1.8 Gt CO₂‑eq/yr. Discrepancies between estimates are driven by the area considered suitable for restoration, types of restoration activities considered and their associated carbon uptake rates, and inclusion of cost constraints. Each of these individual estimates is also associated with substantial uncertainty, and further work is needed to standardize definitions of forest restoration and constrain the range of impact estimates.
Table 5. Climate impact at different levels of adoption.
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | NA |
| Achievable – low | 0.099 |
| Achievable – high | 0.149 |
| Adoption ceiling | 0.198 |
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | NA |
| Achievable – low | 0.115 |
| Achievable – high | 0.173 |
| Adoption ceiling | 0.230 |
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | NA |
| Achievable – low | 0.020 |
| Achievable – high | 0.031 |
| Adoption ceiling | 0.041 |
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | NA |
| Achievable – low | 0.483 |
| Achievable – high | 0.725 |
| Adoption ceiling | 0.966 |
Unit: Gt CO₂‑eq/yr, 100-year basis
| Current adoption | NA |
| Achievable – low | 0.718 |
| Achievable – high | 1.077 |
| Adoption ceiling | 1.437 |
Forests help regulate local climate by reducing temperature extremes (Lawrence et al., 2022; Walton et al., 2016). Zhang et al. (2020) found the land surfaces of restored forests were 1–2 °C cooler than grasslands.
Forest restoration can improve biodiversity and health of the ecosystem, leading to more ecological resilience (DeGroot et al., 2013; Hua et al., 2022). Restored forests can intercept rainfall and attenuate flood risk during extreme rainfall events (Kabeja et al., 2020; Gardon et al., 2020). In some climates, certain reforestation methods could increase ecosystem resilience to wildfires (North et al., 2019).
For a description of the flood benefits, please refer to the “Extreme Weather Events” subsection.
Forest restoration may increase or decrease the ecosystem’s resilience to drought, depending on changes in factors such as evapotranspiration, precipitation, and water storage in vegetation (Andres et al., 2022; Sankey et al., 2020; Teo et al., 2022). For example, Teo et al. (2022) found that reforestation of degraded lands reduced the probability of experiencing extremely dry conditions in water-insecure regions of East Asia.
Forest restoration creates both temporary and permanent job opportunities, especially in rural areas (DeGroot et al., 2013). A study in Brazil found that restoration can generate about 0.42 jobs per hectare of forest undergoing restoration (Brancalion et al., 2022). Restoration of forests may also improve livelihoods and income opportunities based on the ecosystem services the forest provides. While these benefits vary substantially with household and community characteristics, in general, they include income diversification and the availability of food and fiber from forests (Adams et al., 2016). For example, in Burkina Faso, smallholders who restored lands through assisted regeneration diversified their income by harvesting resources such as fodder for livestock and small wildlife (Kumar et al., 2015).
Forests provide income and livelihoods for subsistence households and individuals (de Souza et al., 2016; Herrera et al., 2017; Naidoo et al., 2019). Forest restoration may improve food security for some households by improving incomes and livelihoods.
Reforestation may promote the health of nearby communities. Herrera et al. (2017) found that in rural areas of low- and middle-income countries, household members living downstream of higher tree cover had a lower probability of diarrheal disease. Biodiverse forests are linked to a reduced risk of animal-to-human infections because zoonotic hosts tend to be less abundant in less disturbed ecosystems (Keesing & Ostfeld, 2021; Reddington et al., 2015).
Indigenous peoples have a long history of caring for and shaping landscapes that are rich with biodiversity (Fletcher et al., 2021), and restoring the health and function of forests is essential for protecting indigenous cultural values and practices. Indigenous communities provide vital ecological functions for preserving landscape health, such as seed dispersal and predation (Bliege Bird & Nimmo, 2018). Indigenous peoples also have spiritual and cultural ties to their lands (Garnett et al., 2018). Restoration must be implemented using an equity-centered approach that reduces power imbalances between stakeholders, ensures people are not displaced, and involves local actors (Löfqvist et al., 2023).
Forests are home to a wide range of species and habitats and are essential for safeguarding biodiversity. Reforestation of native forests increases the biodiversity of an ecosystem relative to its previous cleared state (Brancalion et al., 2025; Hua et al., 2022). While many factors, such as the restoration method, time since restoration, and biophysical conditions, can impact restoration, studies of reforestation report increases in biodiversity and more species abundance after restoration, though the biodiversity typically remains below that of intact forests (Crouzeilles et al., 2016; Hua et al., 2022).
The impacts of reforestation on water quality vary based on factors such as geography and time since undergoing restoration (Dib et al., 2023). In general, forests act as natural water filters, maintaining and improving water quality (Dib et al., 2023; Melo et al., 2021). Restoration of forests is associated with improved water quality in streams compared with their previously degraded state (dos Reis Oliveira et al., 2025).
Forest restoration initiatives that are not responsive to local socioeconomic conditions risk displacing community land access and compromising local livelihoods. Effective forest restoration activities can be highly diverse, but must be targeted towards local environmental, sociopolitical, and economic conditions (Stanturf et al., 2019).
If forest restoration encroaches on agricultural lands, it can trigger clearing of forests elsewhere to replace lost agricultural production.
Planting trees in areas where they do not naturally occur, such as in grasslands and savannas, can alter hydrologic cycles and harm biodiversity (Veldman et al., 2015a; Veldman et al., 2015b). The estimates of potential forest restoration area that we use in this analysis are constrained to minimize these risks by including only land that was once forested and not allowing for forest restoration on croplands or in urban areas.
Forest restoration can improve the health and function of adjacent ecosystems that are being protected or restored.
These solutions are all suitable to implement on degraded land, and thus are in competition for the available degraded land.
ha under restoration
CO₂
ha under restoration
CO₂
ha under restoration
CO₂
ha under restoration
CO₂
Forest restoration can divert resources from other climate solutions, including protecting intact forests. Humans clear approximately 0.4% of forests annually (Curtis et al., 2018; Hansen et al., 2013; Sims et al., 2025), and halting further deforestation is an urgent priority with huge benefits for the climate, biodiversity, and other ecosystem services (see Protect Forests). While restoration provides carbon sequestration over a period of decades, preventing deforestation reduces emissions immediately and is typically more cost-effective. Restoration should therefore complement, rather than compete with, efforts to reduce deforestation.
Forest restoration can also decrease the albedo, or reflectivity, of Earth’s surface. This can increase temperatures as more of the sun’s energy is absorbed and reradiated as thermal energy. Albedo effects are most pronounced in boreal and dryland regions, where they reduce the net climate benefits of forest restoration (Hasler et al., 2024).
Consensus of effectiveness in enhancing carbon removal: High
Many scientific studies have evaluated the potential for forest restoration, consistently reporting that forest restoration has potential to provide substantial carbon removal. The effectiveness of forest restoration in terms of carbon uptake per hectare is highly spatially variable, with over 100-fold variability in uptake rates globally (Cook-Patton et al., 2020). These uptake rates have been extensively modeled, though estimates vary with respect to restoration activity (e.g., natural regeneration or plantation establishment) and carbon pools included (e.g., above-ground biomass only, above- and below-ground biomass, or total biomass and soil carbon). For forests undergoing natural regeneration, estimates of effectiveness ranged from 1.0 t CO₂‑eq /ha/yr for biomass in boreal forests (Cook-Patton et al., 2020) to 18.8 t CO₂‑eq /ha/yr for biomass and soils in humid tropical forests in South America (Bernal et al., 2018).
Estimates of the potential climate impacts of forest restoration vary widely, with differences driven largely by variability in the estimates of land area available for forest restoration. The IPCC reported a global technical mitigation potential of 3.9 Gt CO₂‑eq/yr with an uncertainty range of 0.5–10.1 Gt CO₂‑eq/yr, and an economically feasible mitigation potential of 1.6 Gt CO₂‑eq/yr with an uncertainty range of 0.5–3.0 Gt CO₂‑eq/yr (Nabuurs et al., 2022). Cook-Patton et al. (2020) estimated a maximum mitigation potential of 8.91 Gt CO₂‑eq/yr and a mitigation potential of 5.87 Gt CO₂‑eq/yr under existing national commitments. Roe et al. (2021) estimated a technical mitigation potential of 8.47 Gt CO₂‑eq/yr and a cost-effective mitigation potential of 1.53 Gt CO₂‑eq/yr. Griscom et al. (2017) reported a technical mitigation potential of 10.1 Gt CO₂‑eq/yr, though the uncertainty estimates spanned 2.7–17.9 Gt CO₂‑eq/yr. Using a more conservative estimate of the area available for forest restoration than previous studies, Fesenmeyer et al. (2025) estimated that sequestration of 2.2 Gt CO₂‑eq/yr is feasible.
The quantitative results presented in this assessment synthesize findings from 16 global datasets supplemented by four national-scale studies. We recognize that geographic bias in the information underlying global data products creates bias and hope this work inspires research and data sharing on this topic in underrepresented regions.
Reduce Overfishing refers to the use of management actions that decrease fishing effort and therefore cut CO₂ emissions from fishing vessel fuel use on overfished stocks. Advantages include the potential to replenish depleted fish stocks, support ecosystem health, and enhance long-term food and job security. Disadvantages include the short-term reductions in fishing effort needed to allow systems to recover, which could impact local livelihoods and economies. While these interventions are not expected to reach globally meaningful levels of emissions reductions (>0.1 Gt CO₂‑eq/yr ), we conclude that Reduce Overfishing is “Worthwhile” with important ecosystem and social benefits.
Our analysis concludes that, despite its limited global impact for reducing emissions, Reduce Overfishing is a “Worthwhile” climate solution that has other important benefits for ecosystem health and long-term food security.
| Plausible | Could it work? | Yes |
|---|---|---|
| Ready | Is it ready? | Yes |
| Evidence | Are there data to evaluate it? | Yes |
| Effective | Does it consistently work? | Yes |
| Impact | Is it big enough to matter? | No |
| Risk | Is it risky or harmful? | No |
| Cost | Is it cheap? | ? |
Reducing overfishing lowers fuel use and CO₂ emissions from wild capture fishing vessels by reducing fishing effort on overfished stocks. This is typically achieved through management actions, such as seasonal closures, gear restrictions, and catch limits. Fishing effort, whether measured as the hours spent fishing or distance traveled, is generally proportional to fuel use. In addition to immediate reductions in emissions, reducing overfishing can allow overfished stocks to recover, which can lead to reduced future emissions since fuel use is lowered when fish are easier to catch and harvested sustainably.
Reducing fishing effort in locations with depleted and overfished wild fish stocks is expected to reduce emissions from fishing vessels. When stocks are overfished, fishers must exert additional effort, traveling further and/or searching longer to make the same catch, which increases fuel use and CO₂ emissions. Reducing overfishing through management actions, such as harvest control rules, gear restrictions, seasonal closures, stronger enforcement of existing regulations, and establishment of marine protected areas, can help fish stocks recover. Other policy tools, such as reducing harmful fuel subsidies that currently enable many otherwise unprofitable fishing fleets, are also likely to result in lower fuel use and CO₂ emissions. Healthy fish stocks can be caught with lower fishing effort, translating to future fuel savings and reduced CO₂ emissions. Global estimates suggest that reductions in overfishing could avoid up to 0.08 Gt CO₂‑eq/yr, representing almost half of the entire capture fisheries sector's annual emissions (0.18 Gt CO₂‑eq/yr ).
Currently, overfishing affects more than 35% of global wild marine fish stocks, increasing by 1%, on average, every year. Reducing overfishing not only lowers fuel use and emissions but also allows overfished stocks to recover. Healthy fish stocks strengthen marine food webs and contribute to ecosystem resilience and biodiversity. Overfishing has widespread consequences for diverse marine ecosystems, such as kelp forests, where declines in fish have led to overgrazing of the kelp by sea urchins. Over time, management interventions will also likely improve the sustainability and long-term reliability of coastal livelihoods and food security by supporting sustainable fisheries.
Policy and management tools for reducing overfishing and, by extension, fishing-related emissions come with some challenges. For instance, management measures or legal protections may not be fully effective if implementation or enforcement is weak. Management and enforcement can be particularly challenging on the high seas, where jurisdiction is limited or shared across many nations, and where illegal, unreported, and unregulated fishing can be widespread. Even when effective, fish stock recovery can take years to decades, and the costs and trade-offs are unlikely to be evenly distributed across fishing fleets. In the short term, efforts to reduce overfishing could create economic challenges for small-scale fishers who may have fewer resources and less capacity to adapt to management restrictions.
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