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Carbon mitigation efforts in California may be hindered by climate change itself

In 20 years, models predict redwoods will be largely confined to far Northern California, as hotter, drier conditions to the south favor oaks over conifers. Photo by Shane Coffield/UCI
In 20 years, models predict redwoods will be largely confined to far Northern California, as hotter, drier conditions to the south favor oaks over conifers. Photo by Shane Coffield/UCI

July 22 (UPI) -- Policy makers in California are counting on the carbon-capturing abilities of the state's forests and shrublands in order to meet its goal of carbon neutrality by 2045.

Unfortunately, new research -- published Thursday in the journal AGU Advances -- suggests the natural carbon storage capacity of California's forests and shrublands are likely to decline as temperatures rise and droughts strike more frequently.

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Models developed by scientists at the University of California, Irvine, predicted the carbon storage capacity of forests and shrublands in the state will decline by 16 percent by 2045 if climate change trends continue unabated.

Under a more moderate warming scenario, carbon storage is predicted decline by 9 percent.

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"This work highlights the conundrum that climate change poses to the state of California," lead study author Shane Coffield, doctoral candidate in Earth system science at UCI, said in a press release.

"We need our forests and other plant-covered areas to provide a 'natural climate solution' of removing carbon dioxide from the air, but heat and drought caused by the very problem we're trying to solve could make it more difficult to achieve our objectives," Coffield said.

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Plants, including trees and shrubs, absorb CO2 during photosynthesis. Some of that carbon gets trapped indefinitely in their biomass or stored in the soil.

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Like many other governments, California is counting on the carbon storage capabilities of its natural ecosystems -- combined with investments in green energy -- to become carbon neutral by 2045.

The latest findings suggest California will need to make a make a more aggressive transition to green energy than previously planned.

"The emissions scenario that we follow will have a large effect on the carbon storage potential of our forests," said co-author James Randerson, professor of Earth system science at UCI.

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"A more moderate emissions scenario in which we convert to more renewable energy sources leads to about half of the ecosystem carbon [sequestration] loss compared to a more extreme emissions scenario," Randerson said.

Though temperatures are certain to rise as climate change trends continue apace, the current climate models offer divergent forecasts for precipitation in the state.

Most models predict the northern half of the state will get a bit wetter in the decades ahead, while the southern half will get drier.

According to the models developed by Coffield and company, the carbon-capturing abilities of forests and shrublands along the coasts of central and northern California will suffer the most as a result of climate change.

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The models also showed the range of California's famed redwoods will continue to shrink in the coming decades.

By 2045, the tree will be largely constrained to the far north, while hotter, drier conditions to the south will favor oak trees over conifers.

Though the models looked only at the effects of changes in temperature and precipitation on carbon storage in California forests, researchers say their findings are a reminder that wildfires are the primary driver of carbon storage losses.

The negative impacts of wildfires in the region is one reason why another recent study determined grasslands, not forests, were better suited to trap and store carbon in California.

"We hope that this work will inform land management and climate policies so that steps can be taken to protect existing carbon stocks and tree species in the most climate-vulnerable locations," Randerson said.

"Effective management of fire risk is essential for limiting carbon [sequestration] losses throughout much of the state," Randerson said.

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