Forests In Certain Areas Of The World Can Add To Global Warming

Trees absorb planet-heating carbon dioxide, so more of them around should help curb global warming, right?

The answer isn’t straightforward. Researchers have found that leafy canopies may have unintended consequences, especially when they cover places where surfaces do a good job at reflecting sunlight back into space  — think snow, bright soils and grasslands.

Trees in these locations can lower the so-called albedo effect, or the reflectivity of the Earth, and possibly even outweigh the cooling benefits of the carbon storage they provide, according to a study published in Nature, a peer-reviewed journal.

The research raises additional concerns around the climate benefits of forest-based carbon projects, which generate credits for every one ton of CO2 avoided or removed from the atmosphere. Previously researchers have revealed cases of projects overstating claims of emissions reduction benefits. Those greenwashing allegations turned away potential corporate buyers for offsets and subsequently crashed the market. 

While work has been done to bolster the quality of these projects, the findings on the albedo effect highlight a new problem that may have been overlooked. “Despite the potential for albedo to reduce or even negate the climate mitigation benefits of some forest carbon projects, calculating for the effect of albedo is not considered in any carbon-crediting protocols to date,” says one of the paper’s authors, Libby Blanchard, a research associate at the Wilkes Center for Climate Science & Policy at the University of Utah.

William Anderegg, another of the study’s authors, notes small carbon removal registry Isometric’s newest reforestation protocol considers albedo, but he said the registry has not yet issued any credits under this protocol as of Aug. 22.

Other researchers have made similar discoveries: The US Department of Agriculture Forest Service found in a study of satellite data, published in June, that reduced albedo offset roughly half of the non-soil carbon storage benefits of trees. The results “may temper expectations for forest establishment as a means of mitigating global climate change,” the authors wrote. An earlier paper found that forest loss in some mountain areas in the western US actually causes net planetary cooling. A third research group found that changes in albedo brought about by tree planting “offset or even negate the carbon removal benefits” in most locations.

The Nature study authors conclude that carbon offset projects should not be allowed in places where warming induced by lowered albedo outweighs the carbon storage benefit, such as some boreal forests or semi-arid drylands with sparse vegetation.

Alternatively, the authors say, the number of credits a project issues could be reduced to account for the expected changes in albedo.

“As currently configured, [forest-based carbon offset] programs are not delivering much in the way of climate benefits,” Blanchard says.