A Cornell study suggests land models may overestimate future forest carbon storage by up to 30 percent, as hotter, drier conditions slow tree growth despite rising carbon dioxide availability.
Current climate models may significantly overestimate how much carbon forests can store in the future because they fail to account for a newly identified ecological response to climate change: warmer conditions are slowing tree growth despite greater carbon availability, according to a new Cornell University study.
Published in Geophysical Research Letters, the study found that one of the most widely used land models for estimating climate change impacts may overstate forests’ future carbon storage potential by as much as 30 percent.
Forests and land currently play a crucial role in absorbing carbon dioxide emissions. Land ecosystems take up about 27 percent of the carbon dioxide produced by burning fossil fuels, while the ocean absorbs another 25 percent. The remainder stays in the atmosphere, contributing to global warming. The researchers said slower forest growth could reduce land’s ability to store carbon, potentially accelerating warming and its effects in ways not captured by existing climate models.
“Knowing how well the land will be able to keep taking up carbon in the future is really important for knowing how much CO2 you’ll have in the atmosphere, and how much warming you’ll have,” said Brendan Clark, the study’s first author and a postdoctoral researcher at Cornell. “But the land models are probably underestimating the effects of hotter, drier air on actual growth.”
Senior author Daniele Visioni, an assistant professor of earth and atmospheric sciences at Cornell, said the findings point to growing limits in nature’s capacity to buffer climate change.
“The more we look, the clearer it becomes that with further warming it will become harder for nature to keep up,” Visioni said.
Clark and his team drew on recent research from forests in Switzerland, where scientists tracked the growth rates of both broadleaf and coniferous tree species over an eight-year period. That research found that hotter and drier weather reduced growth. Ecologists have now documented the same pattern across North America and say the slower growth may be linked to lower turgor pressure, or the amount of water held inside tree cells.
Using the Swiss data, Clark developed a statistical model to project tree growth and carbon storage through 2069. He then compared those projections with simulations from an open-source and widely used land surface model.
The comparison showed that the land model may overestimate tree growth by a factor of two for broadleaf trees and by a factor of three for coniferous trees.
The gap between the two models highlights the need to better incorporate biological processes that slow tree growth into climate modeling, the researchers said. They added that this omission could partly explain why land models have struggled to accurately represent forest responses so far.
“There can be a disconnect between ecologists and modelers,” Clark said. “It’s important to bring them together, to bring this new idea in the ecology world to the land-modeling community, because I think this is going to be something we need to think about.”
For additional information, Cornell referred readers to a related Cornell Chronicle story.
Cornell University also said it has dedicated television and audio studios available for media interviews.
