Doomsayers and hopemongers alike may need to revise their climate predictions after a study that almost rules out the most optimistic forecasts for global heating while downplaying the likelihood of worst-case scenarios. The international team of scientists involved in the research say they have narrowed the range of probable climate outcomes, which reduces the uncertainty that has long plagued public debate about this field. Their increased confidence about the sensitivity of the climate should ease the job of policymakers and diminish the scope for scepticism but it is far from reassuring for the future of the planet.
Until now, the United Nations intergovernmental panel on climate change has estimated a doubling of atmospheric carbon dioxide from its pre-industrial level of about 280 parts per million has a 66% chance of heating the planet by between 1.5C to 4.5C. In May, atmospheric CO2 reached 417ppm, and is rising by about 2.5ppm per year. Optimists could seize on the lower number to say no action was necessary. Pessimists could point to the higher figure to warn apocalypse was nigh. The study, published in Reviews of Geophysics, shrinks that 66%-likely range of climate sensitivity to between 2.6C and 3.9C, or slightly wider if more uncertainties are included. This smaller band is still dangerously high, which means there is no room for complacency, but the most dire predictions are now considered less probable. Climate sensitivity measures the susceptibility of Earth’s climate to human influence. It has been considered the holy grail of climate science since the first 1.5C to 4.5C estimate in 1979. Numerous papers have been published on the subject, but that range has barely changed until now. The latest, more precise study is likely to be the most influential yet because it is written by more than a dozen experts and draws upon the widest range of evidence, including observed physical processes, historical climate data, and records from the ice age. The lead author of the study, Prof Steve Sherwood of the Climate Change Research Centre at the University of New South Wales, said understanding the potential range of climate sensitivity was crucial.
This confluence of sources has allowed scientists to estimate with a 90% level of probability that climate sensitivity is between 2.3C and 4.7C. The most likely level of climate sensitivity has nudged slightly above 3C.
Earlier this year, a handful of climate models, including some of the world’s most advanced, suggested climate sensitivity could be above 5C, prompting alarm. These high figures were not included in the this week’s study, but many climate scientists regard the recent higher numbers as outliers that should not be taken out of the broader context.
Source: The Guardian
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