Forests across the globe are becoming less efficient at absorbing carbon dioxide from the atmosphere, according to a new study published this week in Proceedings of the National Academy of Sciences. Researchers found that climate change-fueled droughts and hotter temperatures are stunting tree growth and diminishing forests’ capacity to act as critical carbon sinks.
Drought and heat decreasing forest productivity
The study analyzed over 30 years of tree ring data from 38,000 sampling sites across the Northern Hemisphere. Tree rings provide insights into tree growth and productivity over time. Analysis revealed that natural forests are absorbing around 1.19 petagrams less carbon annually compared to 30 years ago, representing a 14% decline in their carbon uptake.
“Our findings suggest that increased heat and water stress are starting to outweigh the benefits of warming, longer growing seasons, and rising atmospheric carbon dioxide for tree growth in forests north of the tropics,” said study co-author Rosie Fisher, climate scientist at the National Center for Atmospheric Research.
Several regions saw significant decreases in productivity, including western North America, southeastern Brazil, central Africa and southeast Asia. Many of these areas have experienced record heatwaves, prolonged droughts and severe wildfires in recent decades.
The reduced uptake of carbon dioxide can amplify climate change. “This suggests the Earth system is becoming progressively less efficient at absorbing the greenhouse gas emissions that drive warming,” Fisher said.
Consequences for climate change mitigation
The results underscore the potential complications of relying on forests as carbon sinks to achieve global climate goals.
“Forests play a significant role in global carbon cycles, absorbing roughly 30% of anthropogenic CO2 emissions,” said study lead author William Anderegg, associate professor of biology at the University of Utah. “These ecosystems are facing increased vulnerability in a warming world. Our findings suggest global forests may be more limited in their ability to alleviate climate change than we hoped.”
Many countries factor forest carbon sequestration into their strategies for meeting net-zero emissions targets under the Paris Agreement. The new findings indicate forests could become saturated with carbon earlier than expected as the planet warms.
|Decrease in carbon uptake
|Western North America
* Table showing regions with significant declines in forest productivity
“The decreased carbon uptake we observe could kickstart positive climate-carbon cycle feedbacks that amplify warming,” Anderegg warned. “Our work highlights that forests are facing mounting challenges today that, if left unchecked by human emissions cuts, imperil their carbon uptake services in the long run.”
Outlook going forward
Researchers said stress from drought, heatwaves and other climate impacts will likely continue decreasing global forest productivity throughout this century if swift climate action is not taken.
However, they noted reforestation efforts and forest management changes could help strengthen carbon sinks.
“While forests in some regions are struggling today, there are opportunities to prepare our forests for the climate of tomorrow through forward-looking policies that support adaptive management,” Fisher said. “Our findings underscore the potential benefits of effective forest management that accounts for changing climate and disturbance regimes.”
The study authors stressed the importance of rapid, deep cuts to greenhouse gas emissions. Curbing global temperature rise would reduce exposure to extreme climate events and related forest die-offs.
“Our work reinforces that both letting temperatures rise into the danger zone of more than 2°C above pre-industrial levels, and continuing to increase the atmospheric CO2 concentration, would be perilous for global forests and the ecosystem services they provide,” Anderegg concluded. “Cutting fossil fuel emissions is critical to help forests help stabilize the climate.”
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