For 25 years, the UN’s Intergovernmental Panel on Climate Change has discussed global warming in terms of a range of temperature increases, ranging from 1.5C to 4.5C by 2100. A new climate sensitivity study, published in the journal Nature, limits this projection to the middle of that range, reducing the range of potential outcomes by more than half. The study projects outcomes in between the best and worst-case scenarios discussed so far, according to the Guardian.
According to the study’s lead author, University of Exeter professor Peter Cox, “Our study all but rules out very low and very high climate sensitivities.”
Predictions have sought to determine the planet’s equilibrium climate sensitivity. This represents the second factor, in addition to humanity’s success with reducing emissions, that would determine the extent of climate change by the end of the century.
The new study offers a more limited range of possibilities, between 2.2C and 3.4C of warming, with an overall estimate of 2.8C. These figures suggest that the world might be safe from the most catastrophic of climate change scenarios.
“Having lower probability for very high sensitivity is reassuring. Very high sensitivity would have made it extremely hard to limit climate change according to the Paris targets,” according to University of Edinburgh climate scientist Gabi Hegerl, who was not involved in the study.
However, other scientists cautioned against framing the research as reason to relax efforts to reduce emissions. The planet has already experienced increases of 1 degree Celsius, and this has led to a rise in extreme weather such as droughts, floods, and wildfires, as well as rising sea levels. Furthermore, the upper end of the study’s new projections would still represent a threat to civilization, according to scientists.
Atmospheric CO2 has risen by about half, from 280 to 407 parts per billion, since the 19th century when the industrial age began. Prior projections for temperature increases have relied primarily on this historical record. The new research, however, focused on “the year-to-year fluctuations in global temperature,” and the relationship between short-term temperature variation and “nudges and bumps” in the world’s climate system, according to University of Reading climate scientist Richard Allan.
According to the researchers, this ruled out some of the more extreme climate scenarios.
However, the study did not consider the possibility of shifts in the climate caused by the domino effect of planetary changes such as melting permafrost and ice sheets or the collapse of the gulf stream.
“There is indeed evidence that the climate system can undergo abrupt changes or ‘tipping points’,” according to Cox.