Climate Cooling Benefits Of Planting Trees Overestimated, Study Says

Most climate-conscious people understand that trees can help slow global warming by taking carbon dioxide from the atmosphere, but a recent study suggests that the climate-cooling advantages of planting trees may be overestimated.

Effects Of Darker Forest

Darker forests can warm the Earth by lowering the albedo of the area they cover, which means they absorb more sunlight and reflect less solar radiation back into space.

In this case, the Earth's surface retains more heat.

Furthermore, trees have a more complex role in the Earth and its atmosphere than simply sequestering carbon dioxide. They also emit chemical molecules such as isoprene and monoterpenes.

These molecules can react with a variety of oxidants, including the hydroxyl radical, which degrades methane, a greenhouse gas that is approximately 80 times more potent in warming the climate than carbon dioxide over a 20-year period.

The reaction with the organic chemicals generated by forests reduces hydroxyl concentrations, slows methane decomposition, and increases greenhouse gas concentrations in the atmosphere.

Given methane's ability to warm the climate, even a small adjustment can have a large impact on atmospheric warming, according to James Weber, a lecturer at the University of Reading in the United Kingdom and the primary study author.

As a result, the climate benefits of tree planting will be greater if methane levels are reduced in the atmosphere by other means.

"Reforestation has a part to play, but it will be more efficient if we do it while also cutting greenhouse gas emissions and anthropogenic pollution," Weber said.

Impact Of Forestation

The molecules that trees emit also react with nitrogen oxides, producing the greenhouse gas ozone, which can warm the atmosphere but also produce aerosol particles that reflect solar energy back into space, resulting in a cooling effect.

To better understand the impact of forestation on climate, researchers evaluated two scenario models.

In one, tree planting was one of the few climate change mitigation techniques, and plant emissions of organic compounds increased levels of greenhouse gases such as ozone and methane in the atmosphere.

With both changes in a forest's ability to reflect sunlight back into space and the scattering of some light away from the Earth by organic aerosols taken into account, forests produced a warming effect that offset approximately 31% of the cooling caused by removing carbon dioxide from the atmosphere.

In the other scenario, which involves a more inclusive effort to mitigate climate change, including environmental management and lower energy-intensive consumption to prevent higher concentrations of greenhouse gases from being emitted into the atmosphere, only 14 to 18 percent of carbon removal was offset after forest warming was taken into account.

According to Weber, the models fail to account for other phenomena that can have an impact on forests, such as wildfires and drought.

Sassan Saatchi, senior scientist at the California Institute of Technology's Jet Propulsion Laboratory and adjunct professor at the University of California, believes that the emphasis should be on protecting existing forests as well as repairing and establishing new ones.

He claims that tree planting makes more sense in some areas than others, and that in some places, like California, protecting forests also entails removing trees to help prevent forest fires and help forests survive in the long run.

How do we really make the mitigation plans that we have long term, because we don't want to just do something that in 10 years, we destroy again," he added.