A Missing Piece in Climate Models: Nature’s Own Emissions - Yale E360

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A fire in the Amazon rainforest.<br>Stock Connection Blue / Alamy Stock Photo

for decades, climate scientists have issued warnings about positive global warming feedbacks, vicious cycles in the earth system in which rising temperatures from burning fossil fuels beget more warming. the best tools we have to understand these feedback mechanisms are climate models, which simulate how the atmosphere, oceans, and land will respond under different emissions scenarios. many feedbacks, like the loss of sea ice as the planet warms, are well-accounted for. others, such as changes in cloud cover, remain far more uncertain but are still included in models. feedbacks in which ecosystems emit more greenhouse gases to the atmosphere are so complex that they are often left out entirely.for example, how much more carbon dioxide will be emitted as wildfires increase? how much more methane will bubble up from fermenting wetlands or seep from thawing permafrost? remarkably, these so-called warming-induced emissions are poorly represented or absent from the most influential climate models — that is, those that inform the assessments of the u.n. intergovernmental panel on climate change (ipcc).a new study from a group of leading climate researchers suggests this information gap could make it even more difficult for nations to limit the rise in global average temperatures to well below 2 degrees c, the target set by the paris climate agreement. the study found that emissions from natural systems could add as much as 0.6 degrees c to the rise in global average temperatures. that’s in line with earlier work that suggests such emissions could shorten by 25 percent the amount of time it takes to exceed 2 degrees c of warming. shortcomings in climate modeling, scientists warn, could lead countries to overestimate how much fossil fuels can be burned before breaching climate targets."><br>For decades, climate scientists have issued warnings about positive global warming feedbacks, vicious cycles in the Earth system in which rising temperatures from burning fossil fuels beget more warming. The best tools we have to understand these feedback mechanisms are climate models, which simulate how the atmosphere, oceans, and land will respond under different emissions scenarios. Many feedbacks, like the loss of sea ice as the planet warms, are well-accounted for. Others, such as changes in cloud cover, remain far more uncertain but are still included in models. Feedbacks in which ecosystems emit more greenhouse gases to the atmosphere are so complex that they are often left out entirely.<br>For example, how much more carbon dioxide will be emitted as wildfires increase? How much more methane will bubble up from fermenting wetlands or seep from thawing permafrost? Remarkably, these so-called warming-induced emissions are poorly represented or absent from the most influential climate models — that is, those that inform the assessments of the U.N. Intergovernmental Panel on Climate Change (IPCC).<br>A new study from a group of leading climate researchers suggests this information gap could make it even more difficult for nations to limit the rise in global average temperatures to well below 2 degrees C, the target set by the Paris Climate Agreement. The study found that emissions from natural systems could add as much as 0.6 degrees C to the rise in global average temperatures. That’s in line with earlier work that suggests such emissions could shorten by 25 percent the amount of time it takes to exceed 2 degrees C of warming. Shortcomings in climate modeling, scientists warn, could lead countries to overestimate how much fossil fuels can be burned before breaching climate targets.

Fires and permafrost melt have caused northern tundra to become a source of emissions, after acting as a sink for millennia.

“If you’re not including all the emissions going into the atmosphere, you’re hamstrung from the get-go,” says Brian Buma, a climate scientist at the Environmental Defense Fund. “People are recognizing that the longer we go without taking these emissions into account, there’s just going to be a bigger gap.”

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“Four decades ago, the scientific community was saying we think there are going to be these surprises in the Earth system as the planet warms,” says Benjamin Poulter, the lead scientist at Spark Climate Solutions, a San Francisco-based nonprofit that aims to identify climate “blind spots,” include them in policy frameworks, and assess the best way to deal with them. “Now, we’re starting to see these feedbacks become the reality.”<br>The biggest sources of warming-induced emissions are wildfires, wetlands, and permafrost — all of which have shown recent indications of rapid change. Since 2001, global carbon emissions from wildfires have increased by 60...