Policies Underestimate Forests’ Full Effect on the Climate

When climate policymakers think about forests, they are usually considering carbon sinks or sources: Forests release carbon when they are cleared, burned or degraded, and absorb carbon as they grow. But a new WRI report demonstrates that policymakers must heed clear evidence that forests are even more important for the climate than previously thought.

A growing body of research reveals that forests interact with the atmosphere in many ways other than through the global carbon cycle, affecting rainfall and temperature from global to local scales. In fact, forests’ non-carbon effects are not only essential for fighting climate change, but for food and water security, human health and the world’s ability to adapt to a warming planet.

How Do Forests Affect the Climate?

Reducing CO2 emissions from forest loss and enhancing carbon removals through forest restoration are critical to achieving global climate goals. Doing so would achieve about 6.5 gigatons of CO2 per year of climate mitigation by 2030, or about one-third of the mitigation required from all sources to keep global warming to or near 1.5 degrees C (2.7 degrees F), the limit scientists say is necessary for preventing the worst effects of climate change.

But forests also have many non-carbon effects that have important yet often overlooked local, regional and global implications — and not all of them push in the same direction as CO2 effects.

Some of the main non-carbon processes through which forests affect the climate include:

• Albedo, or how much of the sun’s energy is reflected into space from a particular surface, affects how much solar energy is absorbed. Light-colored surfaces return a large part of the sun’s energy back to the atmosphere and can have a cooling effect (high albedo). Dark surfaces absorb the rays from the sun and can be warming (low albedo). Dark green tree cover usually absorbs more energy than snow cover, crops or bare soil, warming the air as leaves release that heat, much like the heat radiating from a blacktop road.
• Evapotranspiration, or the role of trees in releasing moisture into the air, produces a cooling effect. This happens when water evaporates from the surface of leaves, as well as when water pulled up through the tree’s roots is released through tiny pores in leaves. These processes function as natural air conditioning, cooling Earth’s surface and near-surface air.
• Surface roughness, or the unevenness of a forest canopy, affects wind speed and turbulence. This turbulence helps lift heat and moisture away from Earth’s surface, providing a cooling effect.
• Aerosols are tiny particles released by forests, such as pollen. Trees also release chemical compounds, such as the ones that give Christmas trees their signature aroma. These particles and compounds interact with the atmosphere in complex ways, such as changing ozone and nitrate concentrations and affecting the color of clouds.

Together, albedo, evapotranspiration, surface roughness and aerosols also affect the generation of clouds, which in turn increase albedo with a cooling effect. 

Beyond Producing Carbon Emissions, How Does Deforestation Affect the Climate?

We know that deforestation is a major contributor to global carbon emissions (alongside fossil fuel and industrial emissions) and thus to warming through the greenhouse effect. But deforestation has even further climate impacts when we take the non-carbon effects of forests into account.

These effects vary by scale, local climate, and perhaps most importantly, by latitude. Here are a few of the most significant impacts of deforestation when we consider non-carbon effects:

Tropical Deforestation Warms the World 50% More than Counting Carbon Alone Suggests

The effects of forest loss on global average temperature differ greatly by latitude.

Tropical forests have an overall global cooling effect — not only from their carbon removal, but also from high rates of evapotranspiration and their ability to stimulate cloud cover (and thereby increase albedo). When we account for the non-carbon effects of tropical deforestation, their estimated contribution to global warming increases by 50% compared to carbon effects alone. In short, keeping tropical forests standing provides massive “bonus” global cooling that current policy ignores.

Boreal forests, on the other hand, have an overall warming effect because their canopy is much darker (lower albedo) than the snow beneath, absorbing solar energy rather than reflecting it back into space. This albedo warming effect is much larger than boreal forests’ combined carbon removal and evapotranspiration cooling effects due to their slow growth rates, resulting in an overall warming from boreal forests’ presence, or overall cooling from their loss. Of course, no one would suggest removing boreal forest cover to fulfill global climate objectives due to the many other benefits that such forests provide — including beneficial local climate regulation.

Deforestation in One Country Can Contribute to Drought in Others

The effects of deforestation on rainfall patterns occur at regional and local scales and depend on factors such as the size of the area deforested and wind patterns.

Large expanses of tropical forest — such as those in the Amazon and Congo Basins — recycle moisture in the atmosphere as it passes across the continents, falls as rain, and then is released by trees through evapotranspiration.

Large-scale deforestation can disrupt this cycle, exacerbating droughts in downwind areas even  hundreds of miles away. For example, researchers estimate that forests in Brazil provide 13-32% of annual precipitation in the downwind countries of Bolivia, Paraguay, Uruguay and Argentina. Deforestation in Brazil can therefore be a major contributor to drought in these countries.

Deforestation Is Causing Warmer Local Average and Extreme Temperatures

The effects of deforestation on local average and extreme temperatures vary by local climate. The most pronounced local warming effects of forest loss are in dry areas. This is because trees in these areas pull water from deep underground, so when they are replaced by barren soil or shallower-rooted crops, the area loses much of the local cooling effect of evapotranspiration.

The most concerning effects of forest loss on local temperature extremes are in the tropics, where already high temperatures make any additional heating especially risky. Studies show that conversion of tropical forests to cropland can increase daytime high temperatures by more than 7 degrees C (12.6 degrees F). Such increases are already affecting crop productivity and exposing people to increased morbidity and mortality due to heat stress. For example, recent studies have documented depressed soy yields in the Cerrado region of Brazil and deaths in a district in Indonesian Borneo linked to deforestation-induced temperature increases.

What Are the Implications of Ignoring the Non-carbon Effects of Forests?

National, regional and local climate mitigation and adaptation policies do not yet account for the non-carbon effects of forests. By failing to take these effects into account, current policies systematically undervalue forests’ climate services, fail to anticipate the full range of climate risks associated with deforestation, and result in an inequitable allocation of responsibilities and resources for climate action within and between nations. For example:

• National climate accounting based on carbon alone results in overstating the global cooling effects of forests in countries at higher latitudes — such as those in Canada, Russia, Scandinavia and the United States — and understating the cooling effects of forests in tropical countries. The contributions to global climate change mitigation from tropical countries like Gabon, Guyana and Papua New Guinea that have maintained a large proportion of their forests are thus systematically undervalued.
• Regional intergovernmental institutions to address the cross-border effects of deforestation on rainfall are lacking. Affected populations in downwind countries can’t represent their interests in decision-making in upwind countries. For example, farmers in Argentina affected by drought have no means to influence land-use decisions in Brazil.
• Thinking about global warming only in terms of global average temperatures masks significant local impacts of deforestation on rising local average and extreme temperatures. The increased risk of heat stress due to deforestation’s local extreme warming will likely have the greatest impact on rural farmers, agricultural workers, and Indigenous and local communities in the tropics.

What Can Policymakers Do to Better Value Forests?

The good news is that there are many opportunities to address the full range of forests’ climate services within the mandates of existing institutions and processes.  Here are a few examples:

Global and national climate policy arenas

There are several ways that the non-carbon climate effects of forests can be incorporated into existing global and national policies.

While the UN Framework Convention on Climate Change’s (UNFCCC) formal objective is to stabilize the concentration of greenhouse gases in the atmosphere, the Paris Agreement provides an opening to include non-carbon effects of forests as a means of limiting warming to 1.5 degrees C, including in the ongoing Global Stocktake. Countries in the tropics could choose to include the additional, non-carbon global cooling benefits of protecting their forests in the national climate plans they submit to the UNFCCC, known as Nationally Determined Contributions (NDCs).

Further, the UNFCCC’s Warsaw Framework for REDD+ provides entry points for recognizing forests’ non-carbon benefits. Its stepwise approach to improving data and methods used for accounting, combined with its explicit encouragement to incentivize the non-carbon benefits of forests, together open the door for countries to quantify, report on and be rewarded for such benefits through REDD+ finance.

Finally, the role of forests’ non-carbon services in reducing risks and enhancing resilience to climate change falls squarely within the UNFCCC’s adaptation framework and can be included in countries’ National Adaptation Plans (NAPs).

Institutions for managing the impacts of deforestation on rainfall

Currently, there are no institutions that govern land management decisions that affect forests’ local and regional effects on rainfall other than via the global carbon cycle. In other words, stakeholders in downwind areas have no way to influence what happens to the upwind forests on which they depend for some portion of their rainfall.

However, such institutions and mechanisms do exist for managing surface water, such as river basin partnerships that span multiple countries, like the Nile Basin Initiative. In some cases, these institutions could expand their membership and mandates to address regional rainfall.

In addition, policymakers can draw lessons from mechanisms designed to govern air pollution, such as Europe’s Convention on Long-Range Transboundary Air Pollution. This Convention, created to address the acid rain problem, provides an example of how decisionmakers can use monitoring, data collection and modelling to inform policy by identifying causes, pathways and critical thresholds.

Institutions such as the World Bank and regional development banks could do more to support such regional cooperation and take the non-carbon regional effects of deforestation into account in their climate and development finance allocations.

National and local land management and adaptation planning

National and local authorities responsible for land-use planning and agricultural policy have several options for integrating forests’ non-carbon climate benefits into existing programs.

Many initiatives are already in place to manage the climate impact of agriculture-related deforestation, such as national REDD+ programs and partnerships with the private sector to get deforestation out of commodity supply chains, such as the Protect, Conserve, Include program in Mato Grosso, Brazil. National and local officials have the authority to address the more immediate and direct risks of forest loss to local agricultural interests — i.e., disruption of rainfall patterns and increased temperature. These local threats are arguably more likely to motivate action compared to appeals to global interests.

As mentioned above, the non-carbon effects of forests on temperature can also be incorporated into national and local adaptation planning. To date, concern about the effects of climate change on human health has focused on increasing global average temperatures, such as expanding ranges of disease vectors and increased exposure to heat stress in urban heat islands. If public health officials understand the magnitude of risks posed to workers and communities in rural areas due to forest cover loss and resulting temperature extremes, they can help advocate for forest protection.

Understanding — and Acting on — Forests’ Full Climate Value

The Not Just Carbon report makes it clear that the science of forest-climate interactions is complex. Further research is needed to fully estimate the additional economic benefits of protecting forests to stabilize the climate, beyond reducing carbon emissions.

Nevertheless, we can already see that the risks to climate stability from losing forests’ non-carbon services is more than enough to justify action now.

It is also clear that a failure to act will exacerbate existing inequities within and between countries. Forests in tropical developing countries will continue to be under-valued in global climate policy, while nearby farmers, workers and Indigenous and local communities will continue to bear the worst of the resulting heat stress and drought from deforestation.

Forests are so much more than just carbon. It’s time to see them for their full climate value — to benefit the people who live and work in and near them, hundreds of miles away, and all around the world. Otherwise, we end up with policies that aren’t “just carbon” — they are likely “not just.”