Clouds Above the Tropics Are Disappearing

August 17, 2016 | Erica Tennenhouse

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Study suggests global temperatures will rise faster than previously thought.

Low-lying clouds over tropical oceans will continue to thin out as the Earth warms, according to predictions made by climate scientists at the Swiss Federal Institute of Technology in Zurich.

The researchers evaluated 15 years worth of data obtained from the radiometers on board NASA satellites, which detailed the amount of sunlight that Earth reflects back into space on a continuous basis.

In agreement with historical simulations and current climate models, the data revealed that, in warmer years, there were fewer low-level clouds floating above the tropics. The researchers report in the Journal of Climate that this trend of decreasing cloud cover is expected continue as Earth’s temperatures rise.

Because clouds have a cooling effect on the climate, accurate predictions of future cloud cover are crucial for determining how much greenhouse gases will heat up the globe over time. This dependence of temperature on greenhouse gases is known as ‘climatic sensitivity,’ and it is notoriously difficult to estimate, due in part to uncertainty over future cloud cover in places like the tropics.

In 2013, the Intergovernmental Panel on Climate Change (IPCC) estimated that the Earth would warm up anywhere between 1.5 and 4.5 degrees Celsius in response to a doubling of carbon dioxide (CO2) levels in the atmosphere.

With their new predictions of future changes in cloud cover, the researchers were able to narrow this broad range. A doubling of atmospheric CO2 will likely result in a 2.3-degree-Celsius global temperature rise at minimum, according to the study.

The new climate sensitivity estimate sits in the upper range of the previous one, meaning that the two-degree temperature rise above pre-industrial levels — which governments agreed not to exceed in the Paris Agreement — may be reached sooner than expected. 

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