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Worst-case global warming forecasts are the most accurate, climate experts say
"There is a 93 percent chance that global warming will exceed 4 ° C by the end of this century," says lead scientist
Current predictions of climate change may significantly underestimate the speed and severity of global warming, according to a new study.
Reassessment of the models that climate scientists use to determine future warming has revealed that less optimistic estimates are more realistic.
The results suggest that the Paris Climate Agreement, which aims to prevent global average temperatures from rising by 2C, may be too ambitious.
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"Our study indicates that if emissions follow a typical routine use scenario, there is a 93% chance that global warming will exceed 4 ° C by the end of this century," said Dr. Ken Caldeira, an atmospheric scientist at the Carnegie. Institution for Science, which is a co-author of the new study.
This probability is an increase from previous estimates, which stood at 62 percent.
Climate models are vital tools for scientists trying to understand the impacts of greenhouse gas emissions. They are built using fundamental knowledge of the physics and climate of the world.
But the climate system is incredibly complex, and as a result, there is disagreement on how best to model the key issues.
This means that scientists have produced dozens of climate models that predict a range of different global warming outcomes resulting from greenhouse gas emissions.
Based on a "business as usual" scenario in which emissions continue at the same rate, climate models vary in their predictions from a 3.2C rise in global temperatures to a 5.9C rise.
The new study, published in the journal Nature, sought to resolve this situation and establish whether the upper or lower estimates are more accurate.
To do this, Dr. Caldeira and his collaborator, Dr. Patrick Brown, reasoned that the most accurate models would be the best at simulating weather patterns in the recent past.
"It makes sense that the models that do the best job of simulating today's observations could be the models with the most reliable predictions," said Dr. Caldeira.
Their conclusion was that the models with higher estimates were more likely to be accurate, with the most likely degree of warming 0.5C higher than the previous best estimates.
Other climate scientists have responded favorably to the new research.
"There have been many previous studies that attempted to compare climate models with past surface temperature measurements, but these have not been found to be conclusive in reducing uncertainty in the range of future temperature projections," said Professor William Collins, meteorologist. of the University. of reading that did not participate in the study.
According to Professor Collins, this work "divides the problem into the fundamental elements of climate change"
Research by Dr. Brown and Dr. Caldeira focuses specifically on models of energy flow from Earth to space, measured by satellites.
They suggest that the amount of sunlight reflected away from the planet by clouds will decrease as the world warms, increasing the magnitude of climate change.
"So now we are more confident about the future climate, but the bad news is that it will be warmer than we thought," said Professor Collins.
According to Professor Mark Maslin, a climatologist at University College London who was not involved in the study, these results could mean "cutting carbon emissions more profoundly and faster than previously thought."
"To achieve these goals, the climate negotiations must ensure that global emissions cuts start as planned in 2020 and continue each year thereafter," said Professor Maslin.
However, experts also warn that care must be taken when predicting such complex phenomena as climate change.
"This is just one line of evidence," said Professor Piers Forster, a climate change specialist at the University of Leeds who was not involved in the study.
“Other lines of evidence based on historically observed warming suggest that simulations with slightly cooler projections may be a better fit. We have to consider all lines of evidence before jumping to conclusions. "
By Josh Gabbatiss
Original article (in English)