Widespread reforestation has buffered the eastern US from climate change

Former forests in the eastern United States have recovered over the past century. In the process, they have kept temperatures stable, or even marginally lower, for tens of millions of people, while the world as a whole warms. The climate discussion about reforestation usually concerns the amount of carbon it can remove from the atmosphere. This finding suggests that regional impacts should not be neglected while considering global impacts.

Americans are far more likely to deny the evidence for climate change, especially those in the Southeast, than their counterparts elsewhere. While this undoubtedly reflects social and historical factors, direct experience can also play a role.

While almost the entire world has gotten warmer, exposing most of the world’s population to increasing heat waves, things have been different in the eastern US. The reason, new research shows, is the recovery of forests that were destroyed in the 18th centurye and 19e centuries.

This information could help calculate how much reforestation other regions would need to protect themselves from global trends.

“The point is to find out how many forests can cool our environment and how big that effect is,” Dr. Mallory Barnes of Indiana University said in a statement. “This knowledge is not only crucial for large-scale reforestation projections aimed at climate mitigation, but also for plans for initiatives such as urban tree planting.”

About 300 years ago, what is now the eastern US was almost entirely forested. Logging and clearing of timber for agriculture has wiped out most of it, but 15 million hectares (37 million acres) have been actively restored or restored through neglect since the 1930s.

Forests cool the air around them by evaporating water, just as we cool ourselves when we sweat, creating clouds at the same time. Other factors, such as the darkness of the leaves and the roughness of the surface, can also have an influence, but outside the poles, transpiration tends to dominate.

During the period of maximum logging, the eastern US likely warmed, but we don’t have good data for most of that time. When the forests returned, they brought with them a regional cooling effect. While all of North America warmed by 0.7°C (1.2°F) between 1900 and 2010, the designated east coast and southeastern regions cooled by 0.3°C (0.5°F).

Barnes and co-authors are far from the first to notice this contradiction with the global trend; professional deniers like to point it out at every opportunity. However, there is debate over its cause, with aerosol releases as pollution, increased rainfall and changes in agricultural activity blamed.

“This widespread history of reforestation, a massive shift in land cover, has not yet been extensively studied to see how it might have contributed to the anomalous lack of warming in the eastern US, which climate scientists call a ‘warming gap,’” says Barnes . said. “That’s why we started doing this work in the first place.”

It’s not news that trees have a cooling effect – you feel it when you enter a green neighborhood – but the magnitude of the effect had to be measured. Barnes and colleagues used data from both satellites and tower thermometers to compare forests with nearby areas that were further away from the ground than in previous studies. They found that even areas that were a significant distance from the forest benefited from the cooling effects.

The team concluded that forests in the eastern US today provide 1 to 2 degrees of cooling during the year, and much more in summer. Since only a small portion of that would have been available from the meager pre-1930s forests, this means that without the regrowth, warming would have been close to that of the rest of the planet. However, they acknowledged that other factors also contributed, with Barnes noting: “We can’t explain all of the cooling, but we suggest that reforestation is an important part of the equation.”

Planting forests is widely hailed as the fastest and easiest way to slow global warming by removing carbon dioxide from the atmosphere. Nevertheless, it is criticized because fires can reverse that effect, and in some locations forests store less carbon than the grasslands they replace.

The authors note that similar caveats also apply to the use of forests in different environments, noting that trees at high latitudes may be warmer than snow-covered tundra. Young forests (20-40 years old) also have a greater cooling effect than old ones, so not all benefits are permanent. “Nature-based climate solutions…will only be effective if they are accompanied by economy-wide decarbonization,” they write.

Nevertheless, if the research can be replicated, it would indicate that reforesting in the right places – or leaving forests standing at all – could make a big difference.

The research has been published in Earth’s Future.

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