Some encouraging new research published this month shows that reforestation can significantly cool the land and air, countering some of the effects of climate change. This might sound like a blinding flash of the obvious. If you’ve ever stood under a tree in a forest or even on a city street, you’ve felt their cooling effect. But this new research by Mallory L. Barnes of Indiana University and her colleagues finds forests can have a cooling effect over a wide region, and the amount of cooling is significant.

“… these findings indicate reforestation has a cooling effect on surface and near-surface air temperature in the EUS [eastern United States], and likely contributed to the slower pace of warming in the region. Both ground- and satellite-based observations indicate that EUS forests cool the land surface by 1–2°C annually (Figure 3) compared to nearby surfaces with short-stature vegetation. During midday in the growing season, surface cooling is 2–5°C (Figures 3c and 4a), and forests aged 25–50 years exhibit the strongest cooling effect (Figure 5c).” [1]

There’s some interesting history here. Following colonial settlement, as much as 90% of forests in the eastern US were cleared for timber and agriculture. But in the early 20th century farmers began abandoning marginal crop land and the government started a major tree planting program. Since then, about 15 million hectares or 58,000 square miles have been reforested. That’s an area larger than England.

Scientists tracking temperature changes across North American noticed a while ago that the eastern US, and especially the southeast, have not warmed as much as expected over the last hundred years. In fact the region has cooled. You can see this “warming hole” highlighted in Figure (c) below.

Barnes and her colleagues have now shown this cooling is at least partially due to the extensive regrowth of temperate forests in this part of the country.

This isn’t a quick fix for global warming. These forests are now 50-100 years old. And planting trees must be done thoughtfully because they don’t have a warming effect everywhere. But it is, um, cool to know that in addition to absorbing and storing large amounts of carbon, forests can help cool some regions of the planet.

References

[1] Barnes, M. L., Zhang, Q., Robeson, S. M., Young, L., Burakowski, E. A., Oishi, A. C., et al. (2024). A century of reforestation reduced anthropogenic warming in the Eastern United States. Earth’s Future, 12, e2023EF003663. https://doi.org/10.1029/2023EF003663.

Related Links

Lester, Liza. “A century of reforestation helped keep the eastern US cool, study finds.” Phys.org, 13 Feb. 2024, https://phys.org/news/2024-02-century-reforestation-eastern-cool.html.

Milman, Oliver. “Very cool: trees stalling effects of global heating in eastern US, study finds.” The Guardian, 17 Feb. 2024, https://www.theguardian.com/environment/2024/feb/17/us-east-trees-warming-hole-study-climate-crisis.