ITHACA, N.Y. - Forests and land play an important role in absorbing carbon dioxide emissions, but current models and forecasts don’t incorporate a new and surprising ecological discovery: Despite more available carbon, climate change and warmer temperatures are slowing forest growth.
A new study from Cornell University, published in Geological Research Letters , considers for the first time the impact of the discovery on climate models, finding that one of the most-used land models for determining the impacts of climate change may overestimate forests’ future potential for carbon storage by as much as 30%.
“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 first author and postdoctoral researcher Brendan Clark. “But the land models are probably underestimating the effects of hotter, drier air on actual growth.”
The land currently absorbs approximately 27% of the carbon dioxide produced from the burning of fossil fuels, with the ocean taking up another 25% and the rest staying in the atmosphere, leading to warming. Slower forest growth could reduce the land’s capacity for carbon storage, accelerating warming and its impacts in a way that’s not currently captured in climate models.
“The more we look, the clearer it becomes that with further warming it will become harder for nature to keep up,” said senior author Daniele Visioni , assistant professor of earth and atmospheric sciences.
Clark and his team used recent research from forests in Switzerland that measured the growth rate of both broadleaf and coniferous tree species over eight years, finding that drier, hotter weather led to reduced growth. Ecologists have found that the slower growth, which has now been documented across North America, may be due to lower turgor pressure, or the amount of water in the tree’s cells.
With the data from Switzerland, Clark built a statistical model that predicts tree growth and carbon storage through 2069 and compared it to simulations from an open-source, widely used land surface model. Clark found that the land model simulations may overestimate tree growth by a factor of 2 for broadleaf trees and a factor of 3 for coniferous trees.
The discrepancy between the two models signals the importance of incorporating the processes that slow growth in modeling more broadly – and could partly account for land models’ inaccuracy to date.
“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, read this Cornell Chronicle story.
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Geophysical Research Letters