What is our assessment?

Based on our analysis, expanding grazing increases methane emissions and often displaces land uses that would deliver greater carbon sequestration and biodiversity outcomes. It is therefore “Not Recommended” as a climate solution. 

What is it?

Expanding grazing includes converting cropland, degraded land, or native landscapes (e.g. forests, savannas) to pasture to increase beef production. As a climate solution, it assumes that soil organic carbon (SOC) can be increased sufficiently to offset methane emissions, resulting in net climate mitigation.

Does it work?

Expanding grazing does not generate net carbon removal because SOC gains are insufficient to offset associated enteric methane emissions. Claims that alternative grazing systems can generate net carbon removal or that grass-finished beef offers climate advantages are not supported by independent scientific evidence, with any gains limited to narrow, context-specific cases that exclude full-scope emissions. SOC gains, where they occur, are slow, saturating, and reversible, while ruminants emit methane continuously. Offsetting global current ruminant emissions would require sequestering 135 Gt of carbon (≈495 Gt CO₂ ) over 100 years, nearly twice the carbon stock in all the world’s managed grasslands. Because sequestration potential is uneven and many regions are degraded or constrained by soil and climate conditions, the required gains, to offset enteric methane emissions, would be concentrated on a subset of lands. This translates into required increases in soil carbon of roughly 25–2,000% locally over 61–225 years. This not only is unlikely, but also overlooks evidence that removing grazing livestock can increase plant growth, biomass, and SOC across grasslands, meaning that expanding grazing would compete with more effective forest or grassland carbon sequestration restoration pathways on degraded lands.

Why are we excited?

Expanding grazing can involve converting intensive cropland, such as land used for biofuels, to perennial pastures, which may increase SOC under low ruminant stocking rates and favorable environmental conditions (see Reduce Grazing Intensity). However, these benefits are driven by perennial vegetation and can be achieved more effectively through restoration approaches that do not introduce ongoing methane emissions.

Why are we concerned?

The core climate concern with expanding grazing is that it introduces cattle, a continuous methane source, on land that could capture carbon below and above ground more rapidly in the absence of cattle grazing. SOC gains under grazing, if they occur, are slow, reversible, and limited by saturation, while emissions from ruminants are immediate and ongoing.

Grazing is already the largest human use of land, and many grazing lands are affected by degradation and overstocking. Approximately 42% of global pastureland could support forests. Restoring these areas could sequester 445 Gt CO₂ by 2100, equivalent to more than a decade of global fossil fuel emissions. In addition, 50% of all global natural nonforest ecosystem conversion between 2005 and 2020 was driven directly by pasture expansion.

Demand for food is rising, while climate change is already reducing agricultural productivity and increasing crop losses. Some projections show a 36 to 50% decline in climatically viable areas for grazing by 2100 due to rising heat and shifting water conditions, alongside risks of broader yield declines. Expanding grazing, which would increase cattle herds and their feed demands, is an inefficient way to increase food supply, converting large amounts of land and feed into relatively small amounts of food. The global food system loses 7.22 quadrillion calories annually through the conversion of crops into animal products and other nonfood uses rather than direct human consumption, enough to feed 7.2 billion people. Cattle are the most inefficient of these pathways, with a 91% caloric loss when crops are converted into beef. Beef production uses 40% of global cropland yet provides only 9% of animal-source calories.

Improving diets and other demand-side changes are critical to avoid expanding grazing. The impacts of beef production exist along a spectrum: more extensive pasture-based systems require more land and typically produce more methane per unit of output, while more intensive, feedlot-based systems use less land per unit of beef but rely more heavily on cropland for feed, antibiotics, and concentrated waste management. Whether expansion occurs through more extensive or intensive systems, beef remains among the most emissions- and land-intensive ways to produce food.

In addition, animal-sourced foods are a major driver of biodiversity and habitat loss globally, with grazing cattle bearing disproportionate responsibility. Beef is the largest single contributor to the loss of biodiversity in Key Biodiversity Areas (KBAs), at around 31% of total biodiversity loss; 60% of KBAs are used for livestock ranching. Expanding grazing therefore reinforces the leading driver of biodiversity loss.

What is our assessment?

Based on our analysis, restoring seagrass ecosystems can remove carbon with no major environmental risks. Despite a likely small climate impact due to the limited area available for restoration and uncertainty around costs, we consider it “Worthwhile.” 

What is it?

Restore Seagrass Ecosystems removes carbon from the air by reestablishing seagrasses – subtidal marine flowering plants with roots – in areas where they were previously destroyed, degraded, or otherwise lost. Seagrasses remove CO₂ from seawater for photosynthesis, accumulating carbon in their biomass that can later break down and settle into sediments on- or off-site. The removal of CO₂ allows seawater to absorb additional CO₂ from the atmosphere. Restoration typically involves seeding or transplanting seedlings and might also require infilling with sediment to compensate for previous sediment loss and accommodate sea-level rise. Seagrass restoration likely also avoids emissions by curtailing the continued loss of sediment carbon due to degradation (e.g., coastal development). 

Does it work?

Restoration of seagrass ecosystems is a relatively new practice in many regions of the world. While its global climate benefit is uncertain but expected to be small (<0.1 Gt CO₂‑eq/yr ), research suggests that restored seagrass ecosystems generally act as net carbon sinks. Nearly 7 Mha of seagrass have been lost worldwide since the 1970s due to a wide range of stressors, such as coastal development and water quality degradation, though it is unclear precisely how much of this loss is restorable. Areas with the greatest observed losses occur in the Tropical Atlantic, Temperate North Atlantic East, Temperate Southern Oceans, and Tropical Indo-Pacific regions.

Why are we excited?

Restoration of seagrass ecosystems provides numerous benefits for the environment and humans. Seagrass meadows can reduce coastal flooding risk while stabilizing seafloor sediment. Restored seagrass ecosystems also increase biodiversity and habitat available for other organisms, including fish and other animals that transiently use seagrass meadows for foraging or as nurseries.

Why are we concerned?

Despite its widespread environmental benefits, seagrass ecosystem restoration can be expensive and is not always successful. In addition, an estimated 33% of its carbon removal benefits can be offset by emissions of methane, a greenhouse gas that microbes can produce using compounds released by seagrass plants. While costs are uncertain, studies suggest they can be high, with a median cost of US$537,140/ha and an average cost of US$979,335/ha (2023 US$), though other regional projects suggest costs can be closer to US$1,200/ha. Also, restoration of seagrasses is not always successful. On average, 55% of seagrass meadows restored succeed (≥50% survival), and future success may be affected by impacts of climate change such as sea-level rise, which is already driving losses of native seagrass meadows. 

What is our assessment?

Based on our analysis, restoring mangrove forests is a highly effective and relatively inexpensive tool for carbon removal, but it has a small climate impact due to the limited global area available for restoration. While the climate impact is probably low, we consider it a “Worthwhile” climate solution because it poses no major risks and provides widespread co-benefits for humans and the environment.

What is it?

Restore Mangrove Forests is a climate solution that removes carbon from the air by re-establishing mangrove ecosystems in areas where they were previously drained, filled, or otherwise degraded and lost. Nearly 2 Mha of mangroves have been destroyed since 1970. As mangrove plants are re-established and grow, they take up CO₂ through photosynthesis and store carbon in above- and below-ground biomass. They also trap and bury carbon-containing sediments, allowing additional carbon to accumulate in waterlogged soils where decomposition is slow. Restoration actions typically involve re-planting and restoring hydrologic conditions to allow tidal exchange with the ocean. Restoration also often replaces land uses that can be sources of large CO₂ (and other GHG) emissions.

Does it work?

Mangrove restoration is a well-established carbon removal approach that has been practiced for at least 40 years in many regions of the world. Research shows that restored mangrove ecosystems can act as large, durable carbon sinks, with sediment carbon likely able to persist for centuries or longer, similar to natural systems. However, because the estimated global area available for restoration is ~1 Mha, its climate impact is expected to be under 0.1 Gt CO₂‑eq/yr. Despite this limitation, restoration can still be a regionally important intervention in certain regions and countries that hold a disproportionate share of restorable mangrove area, due to its high effectiveness. Indonesia (~186,600 ha) and Mexico (~145,500 ha) contain the two largest national areas of restorable mangroves globally. In a relative sense, countries such as Belize, Honduras, Mexico, Nicaragua, Sri Lanka, the United States, and Vietnam are estimated to have at least 10% of their original mangrove area restorable. 

Why are we excited?

Restoration of mangrove ecosystems is an established practice that can be low cost with widespread environmental benefits. Recent global assessments suggest that restoration and natural expansion together added about 393,000 ha of mangrove area from 2000–2020. Restoration can recover ecosystem function, support biodiversity, and reduce exposure to coastal hazards, such as coastal flooding and erosion. Costs can vary from US$3,000–9,800/ha, with the removal of an estimated 0.78 Gt CO₂ over the next 40 years estimated to cost under $20/t CO₂. Low-cost restoration potential is greatest in countries such as Indonesia, Brazil, Mexico, Myanmar, and India. 

Why are we concerned?

This practice, while highly effective at removing carbon, is unlikely to scale to a globally relevant climate impact level given the limited area available for restoration. Although a large area of mangroves has been lost, not all of these areas remain feasible for restoration. For example, nearly 20% of all lost mangrove areas have been converted to open water habitats that are no longer suitable for restoration. Additionally, methane emissions can occur in restored mangroves, which might offset 20% of the carbon removed. Mangrove restoration is also not always successful, and reported outcomes vary widely across projects, with an estimated average success rate of ~62%.

What is our assessment?

Reduced grazing intensity can temporarily reduce soil degradation and erosion. However, SOC outcomes depend on a number of factors, such as climate zone, land use history, soil properties, and grass type. Therefore, until stronger, long-term evidence is available to guide more effective implementation, we will Keep Watching this solution.

What is it?

Reducing grazing intensity refers to lowering ruminant livestock stocking rates or shortening grazing duration to reduce pressure on grazing lands. As a climate solution, it is intended to remove carbon from the atmosphere by increasing SOC through enhanced plant productivity, root inputs, and soil stability. Grazing intensity is typically classified as heavy, moderate, or light, based on the proportion of forage removed per unit time.

Does it work?

In general, while heavy grazing reduces SOC, the effects of grazing intensity on SOC recovery varies with climate zones, grass types, soil properties, and prior land use. Increases in SOC under reduced grazing intensity are largely limited to wetter regions, often with high annual rainfall. In arid and semi-arid regions, which represent a major share of global grazing land, reduced grazing intensity often results in neutral or negative SOC responses. A global review and meta-analysis that normalized SOC to 30 cm depth found that even grazing below carrying capacity was associated with an overall decline in SOC, with gains limited to lower-intensity grazing conditions in specific climate zones.

Why are we excited?

Reducing grazing intensity provides ecological benefits. This usually involves reducing the number of ruminant livestock on a farm, which in turn reduces the farm’s methane emissions, land-use pressure, and threats to biodiversity–at least in isolation. It can reduce soil degradation, erosion, and vegetation loss. It is already practiced in many contexts and requires no new technology or infrastructure, making it easy and relatively low cost as a climate intervention, though not necessarily cost-neutral for ruminant livestock producers.

Why are we concerned?

Several limitations, risks, and trade-offs are associated with reducing grazing intensity as a carbon removal strategy.

First, even low-intensity grazing can prevent ecosystem recovery when pastures are seeded with, or invaded by, aggressive grasses that suppress native plants, prevent tree regrowth where ecologically appropriate, and lock landscapes into lower-biodiversity, grass-dominated states.

Second, SOC gains are limited, slow, and reversible. Soil organic carbon is a finite sink that approaches saturation within decades and can be lost through drought, warming, fire, or management changes. SOC accumulation through reduced grazing intensity has been shown to be a temporary and fragile form of carbon storage. 

Third, SOC gains are difficult to measure and verify. Many studies lack baseline SOC measurements, adequate controls, sufficient duration, and/or adequate soil-depth sampling, making it difficult to attribute carbon gains to grazing intensity. To show an increase in SOC from reduced grazing intensity, an ideal experiment would adopt a before-and-after control intervention at a commercial scale and follow SOC changes for 5–10 years.

Fourth, while reducing grazing intensity compares favorably with alternative grazing when it reduces total stocking numbers, it is still less durable and certain as a carbon removal strategy than protecting intact ecosystems, restoring degraded grasslands, or restoring forests where ecologically appropriate. 

Fifth, reducing grazing intensity often lowers herd sizes, but under rising global beef demand this can simply shift production elsewhere. This underscores the value of improving diets and shifting food system infrastructure away from ruminant consumption rather than simply altering ruminant production practices.

Overall, reducing grazing intensity can reduce some local damage from heavier grazing, but in climate-favorable regions especially, the stronger opportunity is often restoring ecosystems or producing higher-yielding plant-based foods.

What is our assessment?

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 “Worthwhile” solution.

What is it?

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). 

Does it work?

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.

Why are we excited?

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.

Why are we concerned?

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.

What is our assessment?

Our analysis finds that Deploy Ocean Biomass Sinking could have high potential environmental risks, including unknown impacts on marine ecosystems. It is also unclear how effective or durable carbon storage in the deep sea is from this approach. There are likely better alternative uses for terrestrial biomass, and cultivating seaweed at climate-relevant scales is probably not feasible. Even if it were, seaweed would probably provide greater value through other applications. Therefore, Deploy Ocean Biomass Sinking is currently “Not Recommended” as a climate solution.

What is it?

Ocean biomass sinking relies on sinking terrestrial plant material and/or seaweed grown in the ocean to the deep sea or seafloor where it can be stored long-term. Cultivating and sinking seaweed removes carbon from the surface ocean, whereas sinking terrestrial biomass material can help reduce emissions that might otherwise occur if the material instead decomposed on land. While not a current practice, terrestrial biomass grown explicitly for sinking would also constitute a form of carbon removal. When biomass sinks naturally, most of it is degraded into CO₂ or other forms of carbon before reaching the deep sea. Deliberate sinking of biomass might avoid some of this degradation by expediting its delivery to the deep sea, depending on the method used. Once sunk, the biomass and any CO₂ or other forms of carbon produced from its degradation can be isolated from the atmosphere for decades to centuries due to the ocean’s slow circulation times at depth. Biomass sinking can be accomplished using active methods, like submersibles, or passive methods, like letting weighted bundles sink on their own. There has been a recent focus on sinking material in low-oxygen ocean basins (e.g., the Black Sea), which might help further minimize degradation, while improving the durability of sequestered carbon due to the long circulation time-scales typical of these regions.

Does it work?

Global estimates suggest that ~11% of carbon produced in natural seaweed ecosystems might be sequestered at depth, generally defined as below the mixed layer at around 1,000 m. However, very few studies have documented the export efficiency, or the fraction of carbon in surface waters that makes its way to the deep sea, of purposefully sunk terrestrial and seaweed biomass, as this practice is currently in the early stages of development and research. If biomass is quickly sunk, most carbon might make its way to the deep sea, while passive sinking techniques, if slower, could result in higher degradation rates. Sequestration also depends on the storage efficiency and durability of carbon once at depth. Some initial research suggests that biomass degradation may be slowed in low-oxygen basins, but this also remains poorly characterized in field studies. It is similarly unclear how durable the carbon stored below the mixed layer will be over climate-relevant timescales, both in the deep sea in general and in low-oxygen basins specifically.

Why are we excited?

The advantages of ocean biomass sinking include its potential ability to use land-based biomass that might otherwise be degraded in landfills or incinerated, both of which lead to CO₂ emissions. In some regions, seaweed cultivation could help reduce nutrient pollution, provide habitat for marine organisms, and locally buffer against ocean acidification. Estimates of potential climate impacts suggest that ocean biomass sinking using biomass from seaweed farms could theoretically exceed 0.1 Gt CO₂‑eq/yr. Still, those estimates remain highly speculative and require more research. Costs are poorly quantified, but some estimates suggest they could be low to moderately expensive compared to other marine carbon dioxide removal approaches, close to US$100/t CO₂.

Why are we concerned?

Ocean biomass sinking has many environmental and social risks that, though not currently fully understood, could make it unfeasible to deploy the technology at scale. Deep-sea and seafloor ecosystems are highly understudied, and it's unclear how new biomass might alter these unique environments. Potential impacts include increased acidification, nutrient pollution, and oxygen depletion of the deep sea, which could affect diverse marine life. Large-scale seaweed cultivation could reduce phytoplankton abundance, disrupt food webs, and deplete nutrients needed by other ecosystems. Cultivation in open ocean areas might relieve demand for coastal space, but they are often nutrient-poor, and adding nutrients raises serious concerns (see Deploy Ocean Fertilization). Terrestrial biomass sources could introduce contaminants into the ocean due to inadvertent inclusion of plastics or other pollutants in sunken biomass. This practice also comes with social risks. Some countries might disproportionately bear negative impacts wherever biomass is cultivated and/or sunk, as it could alter marine food webs and livelihoods. There could also be issues with public perception due to historical injustices around ocean dumping, potentially impeding future projects without meaningful community engagement and transparency. 

Moreover, there are numerous technical challenges relating to the effectiveness and durability of carbon sequestration. Biomass sources differ in how easily they break down, affecting how much carbon is stored at depth. Sunk biomass could also potentially release other greenhouse gases, such as methane and nitrous oxide. The location where biomass is disposed of also matters, impacting how much carbon reaches and stays at depth. However, all of these factors remain poorly constrained. Operational and technical challenges are also significant. To remove at least 0.1 Gt CO₂‑eq/yr using marine biomass, nearly 7 million ha of ocean – over 60% of the global coastline – could be needed for seaweed cultivation, which is impractical. Measurement and verification pose additional hurdles. In the case of seaweed cultivation, tracking carbon removal requires monitoring both CO₂ uptake at the ocean’s surface and export as well as storage at depth across large spatial and temporal scales. In addition, the opportunity cost of sinking terrestrial biomass is high due to competing land-based uses, as waste biomass and crop residues are finite resources. Growing new biomass explicitly for ocean sinking would introduce new risks, given that land is also a finite resource. Similarly, seaweed probably has higher value and carbon benefits as food, fertilizer, and other products.