Thinning cloud cover threatens two-degree target

Low-level cloud cover in the tropics is thinning as the earth warms up – and threatening the world’s ability to meet the two-degree global warming target, new research has shown.

Low-level cloud cover has a cooling effect on the climate. Because this cloud cover is thinning out, the two-degree global warming target may be reached earlier than many models have predicted, new research has warned.

Determining how far the temperature rise is caused by greenhouse gas is known as climate sensitivity. Researchers from the Federal Institute of Technology in Zurich (ETH), who are behind the new findings, explained that climate sensitivity is a key parameter affecting climate projections and climate targets.

“It’s very unlikely that the climate sensitivity is less than 2.3 degrees Celsius,” explained Tapio Schneider of the ETH. “Climate sensitivity is more likely situated in the upper half of previous estimates, probably around four degrees.”

To reach this estimate, the scientists evaluated a large quantity of satellite data from the past 15 years. The satellites, which continuously measure how much sunlight is reflected from the earth back into space, revealed that in the past, there were fewer low-lying clouds in warmer years than in colder years.

The researchers used this new information to evaluate the quality of around 30 current climate models, finding that almost all were consistent with the observational data – and all the models that matched the observational data also had a climate sensitivity of at least 2.3 degrees Celsius.

As a result, the threshold of two degrees warming that countries committed not to exceed in the Paris Agreement may be reached earlier than anticipated, warned the ETH.

Photo credit: Glen Malley/ CC BY-NC-ND 2.0

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