Scientists Revise Predicted Warming Range to Between 2.6 and 4.1 Degrees Celsius
Earth's temperature is already about 1.2 degrees Celsius above preindustrial levels. Neil Nissing / The Image Bank / Getty Images Plus
Just how hot the earth will get if carbon dioxide doubles from pre-industrial times is a question scientists have wondered about for the past 40 years.
They have generally agreed that the planet will warm 1.5 to 4.5 degrees Celsius above pre-industrial times. Now, a major new study has narrowed that range, revealing we are unlikely to keep global heating below 1.5-degrees Celsius without immediate and dramatic reductions in emissions. They have tightened their range to between 2.6 and 4.1 degrees Celsius, or 4.1 to 8.1 degrees Fahrenheit, according to Science Magazine.
The comprehensive international study released Wednesday and published in Reviews of Geophysics relies on three strands of evidence: trends indicated by contemporary warming, the latest understanding of the feedback effects that can slow or accelerate climate change, and lessons from ancient climates, as Science Magazine reported.
The researchers determined that there was less than a 5 percent chance of a temperature shift below two degrees, and a 6 to 18 percent chance of a higher temperature change than 4.5 degrees Celsius, or 8.1 degrees Fahrenheit, according to The New York Times. The scientists pointed out that the earth's temperature is already about 1.2 degrees Celsius above preindustrial levels, and that, if current emissions trends continue, the doubling of atmospheric carbon dioxide could happen well before the end of this century.
The paper was a collaboration of 25 scientists around the world. The lead author, Steven Sherwood, a climate scientist at the University of New South Wales in Sydney, Australia said that the group's research suggested that these temperature shifts are now unlikely below the low end of the range, according to The New York Times. There is a bright spot, though. The research also suggests that the "alarmingly high sensitivities" of 5 degrees Celsius or higher are extremely unlikely, though they are "not impossible," Sherwood said.
If global heating reaches the midpoint of this new range, it would be extremely damaging, said Kate Marvel, a physicist at NASA's Goddard Institute of Space Studies and Columbia University, who called it the equivalent of a "five-alarm fire" for the planet, as The Washington Post reported.
"The main message is that unfortunately we can't expect that luck will save us from climate change," Reto Knutti, professor of climate physics at ETH Zurich's Institute for Atmospheric and Climate Science, as The Guardian reported.
"The good thing is that we've somewhat narrowed the range of future long-term warming, the bad thing is that we can no longer hope or claim that the problem will just magically go away."
These scientists now say it is likely that human activities — such as burning oil, gas and coal along with deforestation — will push carbon dioxide to dangerous levels that will usher in catastrophic consequences. They say there needs to be a concerted effort to drastically reduce emissions immediately, as The Washington Post reported. Staying below that level is still possible. If steep emissions cuts are made in the near-term, a doubling of carbon dioxide levels could be avoided.
The study of climate sensitivity is to be used by the United Nations's Intergovernmental Panel on Climate Change when it publishes its next major report in 2021 or 2022. As Science Magazine reported, the estimate will also inform projections for sea-level rise, economic damage and much else. A clearer picture of those consequences could do a lot to force local governments to cut emissions and adapt to warming, said Diana Reckien, a climate planning expert at the University of Twente. "The decreasing uncertainty could potentially motivate more jurisdictions to act," she said.
Andrew Dessler, a climate scientist at Texas A&M University who was not involved in the study, called this "a tour de force of climate science." He said via email to The Washington Post that the study "really, really kills the skeptical argument that climate sensitivity is low."
"It would have been great if the skeptics had been correct and climate sensitivity was, say, 1.5°C, but that's not the world we live in."
Correction: A previous version of this article said that we are past any hope of keeping global heating below 1.5-degrees Celsius above pre-industrial times. It has been updated for accuracy to say we are unlikely to keep heating below that threshold.
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