Recent research suggests that climate feedbacks such as thawing permafrost, intensifying boreal-forest fires and warming wetlands could add substantially to human-caused warming. A September synthesis found that thawing permafrost releases additional carbon dioxide and methane, potentially intensifying wildfires, while hotter lakes and reservoirs and warmer, wetter wetlands could raise global average temperatures by an additional 0.2°C to 0.4°C this century. That warming would come on top of the 2.6°C of warming above pre-industrial levels that modelers already project by 2100.
The additional heat could expose cities around the world to large-scale disasters, including months-long heat waves and flooding that could affect millions or potentially billions of people, according to analyses of a 3°C world.
Climate models leave feedbacks out
None of the models used in the major United Nations climate assessment fully accounts for all of these feedback effects. Many do not incorporate them at all. This creates a major blind spot in estimates of how much the world is likely to warm in the coming decades and how quickly countries must cut emissions to remain within critical temperature limits.
A separate analysis published in One Earth in March examined what these feedbacks could mean for international climate targets. It concluded that the world may be further off track than widely believed.
The researchers found that three regional sources of warming emissions—thawing permafrost, increased fires in boreal forests and warming tropical wetlands—could reduce the time required for the planet to exceed sustained warming thresholds of 1.5°C and 2°C by as much as 25%.
Efforts to improve projections
“It is clear that our climate models and UN reports need to be updated to better represent these impacts,” said Sam Abernethy, the paper’s lead author and a climate scientist at Spark Climate Solutions, a nonprofit research group based in San Francisco. He added that countries must also strengthen emissions-reduction efforts to reflect a better understanding of the risks.
Some work to address the problem is already under way. Spark has launched the Intercomparison Project for Greenhouse Gas Emissions Models Associated with Global Warming. More than 20 international teams are conducting the same set of analyses on different models to improve understanding of the potential strength of these feedback effects.
The researchers hope the United Nations will incorporate the results into its next major climate assessment, expected to be published in 2029. That report will update estimates of how much additional carbon dioxide and other greenhouse gases the world can emit before exceeding key temperature benchmarks.
What is already clear, however, is that the planet is warming rapidly and countries are not doing nearly enough to reduce fossil-fuel pollution. Even if emissions are brought under control, warming-related emissions from natural systems are likely to continue.
Source: www.technologyreview.com
