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

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

When it comes to climate solutions, trees are all the rage right now. From the Trillion Tree campaign to the flood of strong – if somewhat vague – pledges 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 policy makers around the world. Even the oil companies are getting in on the action.

But while much ink has been spilled about the potential benefits of planting trees in the fight against climate change, less is known about how the forests we already have will respond to a warmer environment. Some scientists say this is a critical gap in our knowledge of how trees might figure on the global climate agenda. Committing resources to an expensive forest restoration project may not make sense, for example, if it is in an area that is likely to experience climate-related mortalities or a high risk of fire over its lifetime.

A new study published in the journal Science aims to begin to fill this gap. Using a combination of ecosystem and climate models, as well as satellite data on existing disturbances, its authors found that certain forest types have been shown to be particularly susceptible to climate risks, even when human-induced deforestation has been suppressed in as variable. They say these findings could help policymakers develop a more nuanced understanding of the threats facing the planet’s forests and the role they can play in the global climate agenda.

“The future of Earth’s forests in a rapidly changing climate is incredibly uncertain. And that has huge 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 was not the first to attempt to model forest change under various climate scenarios, but Anderegg told Mongabay it was one of the first to combine and compare different approaches to see where their results overlap. .

The models used by the researchers often did not agree and, in some cases, directly contradicted each other. But overall, they showed that the forests of western North America, the drier tropical forests like those in the southeastern Amazon, and the southern boreal forests that cover large swaths of the northern North America and Eurasia are threatened due to climate change.

“These disruptions are things like severe wildfires, drought stress, and pests and pathogens like the bark beetle outbreak in western North America. These are the most important ones, but there can also be more subtle ones like species changes or gradual deaths and high mortality rates,” Anderegg said.

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

The study’s findings paint a less rosy picture of the role tree planting could play in tackling climate change than its proponents would like. A cornerstone of California’s climate strategy, for example, has been a state-funded carbon offset market that included credits generated by forest conservation projects. But in just 10 years, wildfires have nearly wiped out the market’s pool of carbon reserves, destroying offsets that had been bought by companies like Microsoft and raising questions about the market’s overall climate benefits.

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

“The scientific community increasingly recognizes and is concerned that these carbon offsets are not necessarily based on excellent science and do not take the risks of climate change seriously,” he said. -he declares.

The potential climate benefits of reforestation and forest restoration projects remain a hotly debated topic. In some cases, science doesn’t even know whether certain types of forests cool or warm their environment. But most experts say the priority should be protecting the forests that already exist, which means deepening our understanding of the kind of risks they will face in the decades to come.

“We still need these forests, so we will have to protect them,” said Deborah Lawrence, a professor of environmental science at the University of Virginia, who was not involved in the recent study. “That means two things: first, monitoring fires, pests and drought so we can respond quickly. Second, plant new forests along the borders of existing forests to cushion the impact of disturbances that pass through a landscape like fire and pests.

Yet even under the most promising climate scenarios, a warmer planet seems like bad news for some forest types. In the United States and Canada, forestry experts are now wondering if they can help accelerate the “migration” of these forests to safer lands. But Anderegg says that in the meantime, exuberant sales pitches about what trees can do to offset fossil fuel emissions should be given a close, if not skeptical, eye.

“Our study and others like it are really starting to point out that we have to be careful and do it thoughtfully and based on the best available science if we’re going to use forests for climate solutions,” he said. -he declares. “We don’t want to bet big on a set of forests that will then go up in flames in 20 or 30 years.”

Quotes:

Anderegg, WR, Wu, C., Acil, N., Carvalhais, N., Pugh, TA, Sadler, JP and Seidl, R. (2022). An analysis of the climate risks of the earth’s forests in the 21st century. Science, 377(6610), 1099-1103. doi:10.1126/science.abp9723

OnlinePearce, F. (2022). Forest forecasting. Science, 376(6595), 788-791. doi:10.1126/science.add0552

Banner image:A smoldering fire in a boreal forest in Siberia. Image courtesy of Greenpeace International.

boreal forests, carbon market, carbon offsets, climate change, climate science, deforestation, forest carbon, impact of climate change, deforestation of rainforests, destruction of rainforests, threats to rainforests, trees, rainforests

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Teresa H. Sadler