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Even without human-driven deforestation, climate change threatens some forests

A fire smouldering in a boreal forest in Siberia. Image by Greenpeace International.

  • In a study published in Science, researchers analyzed a set of climate and ecosystem models to predict the risks that climate change poses to forests.
  • The models displayed consistent risks to forests in western North America, drier tropical forests like the southeastern Amazon, and northern boreal forests.
  • Researchers say their findings speak to the need to be careful when evaluating the role trees can play as a climate solution.

When it comes to climate solutions, trees are in vogue right now. From the Trillion Tree Campaign to the stream of vigorous — if somewhat vague — promises made at last year’s COP26 climate conference to halt global deforestation, harnessing the carbon-sequestering power of forests has become a goal of governments, cities, and policymakers across the world. Even oil companies are getting in on the action.

But while much ink has been spilled on the potential benefits of tree planting in the fight against climate change, less is known about how the forests we already have will react to a hotter environment. Some scientists say that’s a critical gap in our knowledge of how trees could figure into the global climate agenda. Sinking resources into a costly forest restoration project might not make sense, for example, if it’s in a region that’s likely to see climate-related die-offs or a high risk of fire during its life span.

A new study published in the journal Science aims to start filling that gap. Using a combination of ecosystem and climate models, along with satellite data on existing disturbances, its authors found that some types of forest showed up as particularly sensitive to climate risks — even when human-driven deforestation was removed as a variable. They say those findings could help policymakers develop a more nuanced understanding of what threats the planet’s forests face, and what role they can be expected to play in the global climate agenda.

“The future of Earth’s forests in a rapidly changing climate is incredibly uncertain. And that has enormous implications for communities, for the economy, and for the atmosphere itself,” said William Anderegg, an associate professor at the University of Utah and one of the study’s authors.

The study wasn’t the first to try to model forest changes under various climate scenarios, but Anderegg told Mongabay that it was one of the first that combined and compared different approaches to see where their findings overlapped.

The models that the researchers used often didn’t agree — and in some instances directly contradicted each other. But overall they showed that forests in western North America, drier tropical forests like those in the southeastern Amazon, and the southern boreal forests that blanket vast swaths of northern North America and Eurasia are at risk due to climate change.

“These disturbances are things like severe wildfire, drought stress, and pests and pathogens like the bark beetle outbreak in western North America. Those are the biggest ones, but there can also be more subtle ones like changes in species or gradual die-offs and elevated mortality rates,” Anderegg said.

A firefighter battling blazes in California. Image by NOAA / Creative Commons.

The study’s findings paint a less rosy picture of the role that tree planting could play in fighting climate change than its boosters might like. A cornerstone of California’s climate strategy, for example, has been a state-financed carbon offset market that included credits generated from forest conservation projects. But in just 10 years, wildfires have almost entirely wiped out the market’s carbon reserve pool, destroying offsets that had been purchased by corporations like Microsoft and raising questions about the market’s overall climate benefits.

If the models analyzed by the Science study are correct, California’s troubles are likely just beginning. According to Anderegg, that should be a wake-up call that tree-planting and carbon offset projects have to be planned much more rigorously and with a deeper understanding of how climate change itself might threaten their viability.

“There’s been this growing recognition and sense of concern in the scientific community that these carbon offsets are not necessarily based on great scientific data and that they aren’t taking the risks of climate change seriously,” he said.

The potential climate benefits of reforestation and forest restoration projects remain a hotly contested subject. In some cases the science isn’t even settled over whether certain kinds of forests cool their surroundings down or heat them up. But most experts say the priority should be to protect forests that already exist, which means deepening our understanding of what kind of risks they will face in the coming decades.

“We still need those forests, so we will need to protect them,” said Deborah Lawrence, a professor of environmental science at the University of Virginia, who wasn’t involved in the recent study. “That means two things: first, monitor for fire, pests and drought so we can react quickly. Second, plant new forests along the borders of existing forests to buffer the impact of disturbances that march across a landscape like fire and pests.”

Still, even under the more hopeful climate scenarios, a hotter planet looks likely to be bad news for some types of forest. In the U.S. and Canada, forestry experts are now considering whether they can help accelerate the “migration” of those forests to safer ground. But Anderegg says that in the meantime, exuberant sales pitches about what trees can to do compensate for fossil fuel emissions should be given a careful — even skeptical — eye.

“Our study and other studies like it are starting to really highlight that we need to be careful and proceed thoughtfully and based on the best available science if we’re going to use forests for climate solutions,” he said. “We don’t want to bet big on a set of forests that then goes up in flames in 20 or 30 years.”


Anderegg, W. R., Wu, C., Acil, N., Carvalhais, N., Pugh, T. A., Sadler, J. P., & Seidl, R. (2022). A climate risk analysis of earth’s forests in the 21st century. Science377(6610), 1099-1103. doi:10.1126/science.abp9723

Pearce, F. (2022). The forest forecast. Science376(6595), 788-791. doi:10.1126/science.add0552

Banner image:A fire smouldering in a boreal forest in Siberia. Image by Greenpeace International.

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