A recently published study analyzes four key functions of forests that together make it possible to increase the cooling function of the planet by up to 50%.
The research also examines the changes that deforestation is causing in rainfall and how these variations affect agriculture.
When thinking about forests and their relationship with climate change, the first thing that is considered is their function to absorb or eliminate carbon, but each time new scientific studies are added that put more arguments on the table that add to the urgency to conserve these ecosystems. Recent research, for example, shows how tropical forests, in addition to being vital for achieving climate balance, are also an important link in rain cycles and, therefore, for agriculture.
The study “Not just carbon: Capturing all the benefits of forests for stabilizing the climate from local to global scales,” published in October of 2022 by the World Resources Institute (WRI) concludes that, in addition to carbon, other functions that tropical forests have that contribute to maintaining climate balance must be considered.
Scientists Frances Seymour, Michael Wolosin and Erin Gray, authors of the research, analyzed four forms of interaction between tropical forests and the atmosphere that would contribute to global cooling up to 50% more than what only the carbon cycle offers.
Why do forests matter?
“It has long been widely recognized that forests have many values and benefits in addition to carbon, such as non-timber forest products or regulation of surface water; but our focus is particularly on interactions with the atmosphere and therefore impacts on climate stability,” says Frances Seymour, study co-author, WRI Forest Program Principal Investigator and one of the world’s leading authorities on sustainable development.
Seymor highlights the contribution of tropical forests to global cooling and says that the main conclusion of his study is that “tropical forests are much more important than we thought for global cooling.”
One of the four interactions between forests and the atmosphere addressed in the study is the ‘albedo effect,’ that is, the amount of sunlight that is reflected back into the atmosphere from a particular surface. Consistent with this effect, light-colored surfaces return a large part of the sun’s energy to the atmosphere and can have a cooling effect; while the dark ones absorb the sun’s rays and keep the heat.
In the case of tropical forests, the dark green tree canopy generally absorbs more energy than, say, a snow-covered area, so the air warms as the leaves release that heat. Given this, the question is: why can the albedo effect in tropical forests contribute to the cooling of the planet if what it causes is more heat?
The answer is found when other forest functions are analyzed, such as evapotranspiration, the roughness of the surface of the trees, and the aerosols released by these ecosystems.
Evapotranspiration —explained in the study— refers to the release of moisture into the air that trees generate through their leaves and that produces a cooling effect, “like natural air conditioning, cooling the surface of the Earth and the air close to this surface.”
As for the roughness or irregularity of a forest canopy, research shows that this function affects wind speed and turbulence, in such a way that it helps to move heat and humidity away from the Earth’s surface.
Finally, aerosols, that is, those tiny particles released by forests—such as pollen or chemical compounds that give trees their characteristic scent—interact with the atmosphere in complex ways to the point that they can change ozone concentrations and nitrate and affect cloud color.
“The understanding that these processes are occurring and that they are important is not new. In fact, the effect of albedo on the reflectivity of forests was mentioned in the first IPCC [Intergovernmental Panel on Climate Change] report before the carbon effect of forests was mentioned. But our ability to reduce uncertainty around Each of these effects has improved enough to be able to add them up, and the ability to compare them to the carbon effect has also improved,” explains study co-author Michael Wolosin, a policy expert on reducing emissions from global deforestation and CEO of Conservation International’s (CI) Roadmap for Natural Climate Solutions.
“The 50% estimate is essentially a cooling ‘bonus’ on top of any amount of CO2 emissions that would have been avoided by deforestation. So, for whatever amount of cooling is gained from avoiding CO2 emissions in forests, another 50% additional cooling would be added as a result of the other functions of forests beyond the carbon cycle,” Wolosin explains.
Wolosin gives an example: “If we get 2.8 Gt/yr (gigatonnes per year) of CO2 emissions avoided from tropical deforestation, we would get another 50% extra bonus for non-CO2 effects equivalent to cooling another 1.4 GtCO2 of emissions avoided.”
The international Conservation expert believes that it is time to bring this issue to the negotiating table on climate change and global warming that is currently being discussed at the United Nations Conference on Climate Change 2022 (COP 27), which is being held in Sharm El Sheikh, Egypt. “We will be there, and we will talk about this report. I think it is an opportunity now that the world is focused on climate and its impacts. We hope to really draw attention to the services that forests provide to people.”
The impact on agriculture
The study also addresses the effects of deforestation on rainfall patterns and the temperature of a given location. For example, large expanses of forests, such as the Amazon, recycle moisture from the atmosphere to later transform it into rain that the trees release through evapotranspiration. However, the report explains, when large-scale deforestation occurs, this cycle is interrupted, increasing droughts even hundreds of kilometers away from the place where the forest has been lost.
“Researchers estimate that Brazil’s forests provide between 13% and 32% of the annual precipitation in Bolivia, Paraguay, Uruguay and Argentina. Therefore, deforestation in Brazil may be one of the main contributors to drought in other countries,” the research indicates.
Seymour points out that if the Amazon rainforest continues to be destroyed, the risk of interruption of the rains will be greater, not only within the region, but also in areas distant from it. In addition, the expert points out that it must be taken into account how this will affect agriculture.
The researcher mentions that one of the changes that occurs in rainfall, as a consequence of deforestation, is the shortening of the rainy season. “One of the big reasons why Brazil, for example, has been an agricultural powerhouse is that it has a long rainy season, which has allowed for a double harvest per year. However, if that rainy season is shortened, there will no longer be double cropping and that would have a great impact on the agricultural sector.”
Deforestation has other effects on the climate. The research warns that the most worrisome effects are in the tropics, “where high temperatures make any further warming especially risky.” Thus, the document specifies —based on previous studies— that when tropical forests are converted into farmland, maximum temperatures during the day can increase by more than 7 degrees Celsius. “These increases are affecting crop productivity and exposing people to increased morbidity and mortality due to heat stress,” the document states.
Seymour mentions a study that showed how the increase in temperature affected soybean crops in Brazil. “What was detected was a temperature effect up to 50 kilometers away, so with the increase in deforestation, extreme temperatures increase and affect crop yields, so it is definitely a threat to agriculture in the region,” she adds.
These changes not only cause changes in the environment, but also in food security and people’s health, warns the WRI expert. “When it comes to human health or crops, it is the extremes that are important. The loss of crops or the inability to work under the sun due to extreme heat are some of the implications for people that we present in our report.”
Rural workers in the tropics are some of the poorest and most vulnerable people on the planet, Seymour adds, and they will be directly and immediately affected by increases in temperature, due to the loss of forests. “We are systematically exacerbating existing inequalities. That’s not fair. In order to have a fairer climate policy, we must take these impacts into account,” she specifies.
Michael Wolosin mentions that it can be assumed that there will be impacts even in dry tropical areas, because in those places it is already very hot, therefore, if there is a slight increase in temperatures, the risks of exceeding the heat limits are greater. “We can say that communities around deforestation in the tropics are going to face these impacts, but more research is needed to estimate the magnitude of the effects and understand how it will affect different crops around the world.”
For this reason, Wolosin believes that agriculture should be included in the conversation about protecting forests. “I think the idea is that this could change the politics of the optimal land use conversation, and instead of thinking about agriculture versus forests we should talk about agriculture and forests, because agriculture depends on maintaining forest cover.”
For Seymour, moreover, it is unfair if all the functions of forests are not considered in global climate policy. “We are rewarding countries for their climate action based on carbon accounting alone, but tropical countries fall short because we systematically underestimate the value of their efforts to protect forests. We should actually pay more to protect tropical forests.”