Climate Change: Brazilian Deforestation Will Cause Local Warming of 1.45 °C

At the current rate of deforestation, Brazil will soon feel the heat -- and so will everyone else.

The Amazon Rainforest in Brazil encompasses 2 million square miles of vegetation, sometimes referred to as the “lungs of the planet.” This huge expanse captures huge amounts of the carbon dioxide we expel into the air, breathing oxygen out. But deforestation in these forests is a politically tense issue, and it’s only getting hotter. On Wednesday, scientists warned in Plos One that Brazil’s current rate of deforestation won’t only deplete its unique tropical forests but change the local climate as well.

In the paper, scientists from the Rio de Janiero State University and the University of California Santa Cruz show that the current rate of deforestation in Brazil is leading to a local temperature increase of 1.45 degrees Celsius by 2050.

The UN Intergovernmental Panel on Climate Change (IPCC)’s limit for global temperature increase is 1.5 degrees Celsius. In its latest report, it warned that any additional warming over that limit could cause devastating floods, storms and droughts and urged countries around the world to help stop us from reaching that critical threshold.

Brazil is a key factor in the future of the planet, but limiting deforestation will not be easy with its new president Jair Bolsonaro, who has promised to convert forests into farmland to supply the planet with more beef and more soy.

Tree cover in critical forest regions in Brazil, like the Amazon, could help mitigate the effects of climate change. 

Wikimedia Commons 

The authors of the new paper argue that restoring and protecting Brazil’s forests could halt the march toward 1.5 degrees.

The country actually already has a policy to protect the Amazon called the Brazilian Forest Code. It regulates how much land in key areas like the Amazon rainforest can be farmed (and deforested), and how much of the previously deforested land has to be restored. But in recent years, the Forest Code has undergone some big changes to limit its power. In 2012, a new article was introduced, relaxing laws requiring private landowners to protect a certain percentage of forest on their land. Some scientists argue this act opens up an additional 6.5–15.4 million hectares of private land for legal deforestation.

In the study, study authors Barry Sinervo, Ph.D, and Jayme Prevedello Ph.D., at Rio de Janiero State University, used a new structural equation model to simulate two scenarios: one in which Brazil adheres to the original Forest Code, and one in which it doesn’t and continues to permit illegal deforestation. In the latter “business as usual” scenario, they show that a 1.45 degree increase will occur by 2050. But when regulations are upheld and followed, the increase in temperature by 2050 is only 0.02 degrees Celsius.

One reason the authors stand by the Forest Code to mitigate the effects of climate change is because their analysis of historical data has shown that destroying and restoring forests have opposite effects on climate. This should come as no surprise: When they analyzed climate and forestation data from 2000 through 2010, they found that in tropical areas, places with forest cover losses of roughly 50 percent experienced a one-degree increase in land surface temperature. Conversely, locations where more at least 50 percent more trees were planted saw cooling effects — roughly 1.11 degrees Celsius over ten years.

This effect, they argue, drives home the importance of regulations like the Forest Code, not only for the current state of the environment, but for the future. And their warning couldn’t come at a better time. Already, Bolsonaro has proposed building 541-mile paved highway through the Amazon and has indicated that he will limit the powers of Brazil’s environmental agencies.

Sinervo and Prevedello make a clear statement about how forests can play crucial protective roles in the planet’s health in the present but also in the future: “Our study case of Brazil illustrates that current land use policies can impact future local climate,” they write.

But their analysis also stands as a warning. They argue that we have the tools to help slow our process toward the 1.5-degree temperature increase, but dangerous politicians could allow them to disappear.

Changing forest cover is a key driver of local climate change worldwide, as it affects both albedo and evapotranspiration (ET). Deforestation and forestation are predicted to have opposing influences on surface albedo and ET rates, and thus impact local surface temperatures differently. Relationships between forest change, albedo, ET, and local temperatures may further vary regionally, as the strengths of warming by albedo effects and cooling by ET effects vary with latitude. Despite these important relationships, the magnitude of forest cover effects on local surface temperature across the globe remains unclear. Using recently-released global forest change data, we first show that forestation and deforestation have pervasive and opposite effects on LST, ET and albedo worldwide. Deforestation from 2000 to 2010 caused consistent warming of 0.38 ± 0.02 (mean ± SE) and 0.16 ± 0.01 ̊C in tropical and temperate regions respectively, while forestation caused cooling in those regions of -0.18 ± 0.02 and -0.19 ± 0.02 ̊C. Tropical forests were particularly sensitive to the climate effects of forest change, with forest cover losses of ~50% associated with increased LST of 1.08 ± 0.25 ̊C, whereas similar forest cover gains decreased LST by -1.11 ± 0.26 ̊C. Secondly, based on a new structural equation model, we show that these changes on LST were largely mediated by changes in albedo and ET. Finally, based on this model, we show that predicted forest changes in Brazil associated with a business-as-usual land use scenario through 2050 may increase LST up to 1.45 ̊C. Our results contribute to a better under- standing of the mechanistic inter-relationships between forest change and changes in albedo, ET and LST, and provide additional evidence that forestation has the potential to reverse deforestation impacts on local climate, especially in tropical and temperate regions.

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