- Trees are a crucial regulating factor in the cycle of water and heat exchange between Earth’s surface and atmosphere – and thus forests play a key role in regulating local climates and surface temperatures, according to the authors of the study.
- The researchers discovered that forests often help keep temperate and tropical regions cooler, while contributing to warming in northern high-latitude areas.
- “Forests play a more important role in cooling the surface in almost all regions of the Earth than was previously thought,” Kaiguang Zhao, an assistant professor of environment modeling and spatial analysis at The Ohio State University and a co-author of the study, said in a statement.
It’s estimated that deforestation is responsible for about 10 percent of global carbon emissions. Of course, in addition to the direct emissions created, the destruction of a forest means the removal of a valuable carbon sink, as well, which is why deforestation represents a “double jeopardy” scenario for Earth’s climate system.
These are just two of the chief reasons why efforts to keep forests standing are considered critical if we’re to halt climate change. But according to a new study published in the journal Nature Climate Change late last month, we may be underestimating the extent to which forest conservation and reforestation initiatives can help curb rising global temperatures, as sequestering carbon dioxide is only one of the climate-regulating attributes inherent to the world’s forests.
Trees are also a crucial regulating factor in the cycle of water and heat exchange between Earth’s surface and atmosphere – and thus forests play a key role in regulating local climates and surface temperatures, according to the authors of the study.
“Forests play a more important role in cooling the surface in almost all regions of the Earth than was previously thought,” Kaiguang Zhao, an assistant professor of environment modeling and spatial analysis at The Ohio State University and a co-author of the study, said in a statement. “This really affirms the value of forest conservation and protection policies in the fight against climate change.”
In order to get a more complete picture of how land-use changes – such as conversion of forests to agricultural land or pastureland – can influence local climatic conditions, Zhao and colleagues created a model that combines locally collected meteorological data with extensive records derived from satellites and other Earth observation systems.
After observing the differences in surface-atmosphere heat exchange between forests and areas converted into farms or pastures, the researchers were able to estimate the surface temperature change caused by switching the land from one type of dominant vegetation to another. They discovered that forests often help keep temperate and tropical regions cooler, while contributing to warming in northern high-latitude areas.
“We find that forest cover gains lead to an annual cooling in all regions south of the upper conterminous United States, northern Europe, and Siberia – reinforcing the attractiveness of re-/afforestation as a local mitigation and adaptation measure in these regions,” the researchers write in the study.
The researchers also examined the mechanisms that allow forests to help regulate surface temperatures and found that the transfer of water and heat from the land to the atmosphere via the processes of convection and evapotranspiration might be even more important than scientists previously thought – possibly even wielding a more significant influence in some areas than the sun.
Past research that focused on albedo, or how much of the sun’s light is reflected back into Earth’s atmosphere after hitting the planet’s surface, as a measure of how forests can shape local climates has had inconclusive results, Zhao said. Forests, which tend to be darker than cropland or pastureland, absorb more heat and, in some cases, increase local temperatures, he added. Yet the results of the present study clearly show that forests can and often do lead to local cooling of surface temperatures.
Ryan Bright of the Norwegian Institute for Bioeconomy Research, the study’s lead author, said that while it’s true forests often absorb more solar radiation than grasslands or agricultural lands, they also release more moisture into the air than the shorter vegetation found on farms or pastures. Thus, while replanting a forest that has been chopped down may lead to an albedo decrease (in other words, more solar energy being absorbed), that reforestation project could still “effect a cooling at the surface owing to enhanced evapotranspiration and turbulent mixing of air – two key non-radiative drivers of the surface energy balance,” Bright and his co-authors write.
“What we are finding is that these mechanisms are often more important, even in some of the higher-latitude regions, where surface light reflection has been given more weight,” Bright added.
These results suggest that non-radiative mechanisms such as evapotranspiration must be more fully taken into account by land managers and policymakers when designing local land-based climate mitigation or adaptation policies, Bright said.
“In a world facing increasing competition for land resources for food and livestock production, sensible forest protection policies will be especially critical in our efforts to mitigate climate change, particularly local warming,” he noted. “Our research could help in the identification of regions where forest protection, re-forestation or policies promoting the creation of new forests should be started or ramped up.”
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