Clouds, like blankets, trap heat and are melting the Greenland Ice Sheet

January 12, 2016
A new study shows clouds are playing a larger role in heating the Greenland Ice Sheet than scientists previously believed, raising its temperature by 2 to 3 degrees compared to cloudless skies and accounting for as much as 30 percent of the ice sheet melt. Credit: Hannes Grobe

The Greenland Ice Sheet is the second largest ice sheet in the world and it's melting rapidly, likely driving almost a third of global sea level rise.

A new study shows clouds are playing a larger role in that process than scientists previously believed.

"Over the next 80 years, we could be dealing with another foot of sea level rise around the world," says Tristan L'Ecuyer, professor in the Department of Atmospheric and Oceanic Sciences at the University of Wisconsin-Madison and co-author of the study. "Parts of Miami and New York City are less than two feet above sea level; another foot of sea level rise and suddenly you have water in the city."

The study, published today (Jan. 12, 2016) in Nature Communications and led by the University of Leuven in Belgium, shows that clouds are raising the temperature of the Greenland Ice Sheet by 2 to 3 degrees compared to cloudless skies and accounting for as much as 30 percent of the ice sheet melt.

Numerous statements in the Nobel Peace Prize-winning 2007 Intergovernmental Panel on Climate Change report address the need to better account for clouds in climate models, L'Ecuyer says. Arctic clouds are no exception, especially since climate models have not kept pace with the rate of melting actually observed on the Greenland Ice Sheet.

"With climate change at the back of our minds, and the disastrous consequences of a global sea level rise, we need to understand these processes to make more reliable projections for the future," says Kristof Van Tricht, the University of Leuven graduate student who led the study. "Clouds are more important for that purpose than we used to think."

But in order to better understand them, the right technology needed to be in place.

"Within the last 10 years, NASA launched two satellites that have just completely changed our view of what clouds look like around the planet," says L'Ecuyer, who is affiliated with the UW-Madison Space Science and Engineering Center, where satellite meteorology was born. "Once you know what the clouds look like, you know how much sunlight they're going to reflect and how much heat from Earth's surface they're going to keep in."

When it comes to heat, clouds essentially behave in two ways: They either cool the Earth's surface by reflecting sunlight back into space, or, like a thick blanket, they trap heat at the surface—the greenhouse effect of clouds. On Greenland, which is covered in bright, light-reflecting snow, clouds primarily act to trap heat.

Using the two satellites—CloudSat and CALIPSO—L'Ecuyer was able to take "X-ray images" of Greenland's clouds from space between 2007 and 2010 and determine their structure, how high they were in the atmosphere, their vertical thickness, and their composition (ice or liquid).

The Belgian team combined this data with ground-based observations, snow model simulations and climate model data to map the net effect of clouds. They learned that cloud cover prevents the ice that melts in the sunlight of day from refreezing at night.

"A snowpack is like a frozen sponge that melts during the day," says Van Tricht, who spent six weeks in Madison last year working with L'Ecuyer. "At night, clear skies make a large amount of meltwater in the sponge refreeze. When the sky is overcast, by contrast, the temperature remains too high and only some of the water refreezes. As a result, the sponge is saturated more quickly and excess meltwater drains away."

Researchers already know that while clouds can change the climate, the climate can also change clouds, a phenomenon known as cloud-climate feedback. L'Ecuyer is optimistic that the study—a good example of how satellites are helping us solve the complicated cloud-climate feedback problem—will improve future climate models, to help scientists and policymakers across the world adapt to climate change.

With a background in physics, L'Ecuyer is driven to study clouds by a desire to better understand how people and society are affected by the natural world. "Many of the countries most susceptible to sea level rise tend to be the poorest; they don't have the money to deal with it," he says. "This is something we have to get right if we want to predict the future."

Explore further: Meltwater from the Greenland ice sheet releasing faster

More information: Nature Communications, dx.doi.org/10.1038/ncomms10266

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Moltvic
3 / 5 (2) Jan 12, 2016
There was a study of the global land heat over the United States the two days following 9/11. With no plane-made clouds, they noticed that it was actually warmer a couple of degrees.

There's a good NOVA about it.
classicplastic
5 / 5 (1) Jan 13, 2016
There was a study of the global land heat over the United States the two days following 9/11. With no plane-made clouds, they noticed that it was actually warmer a couple of degrees.

There's a good NOVA about it.

Good catch!

The title of the program is "Global Dimming." https://en.wikipe..._dimming

In short, by using water "pan evaporation" rates that have been recorded daily all over the world for many decades, it has been unquestionably determined that the amount of solar energy hitting the earth and warming it up into infrared, which atmospheric CO2 blocks in an escape back into space, is going down: About 10% over the past three decades.

What's happening is that air pollution particulates form more clouds, which (like mirrors) reflect energy back into space before it hits the earth. This is measured by how fast water evaporates from photons hitting individual molecules and it's very accurate measurement method.

(cont)
classicplastic
5 / 5 (1) Jan 13, 2016
Pan Evaporation continued:..

For the few days after 9/11, with clear skies from aircraft groundings, the US pan evaporation rate, and hence the amount of energy reaching the earth's surface from the decreased albedo, immediately went WAY up, to return to baseline right after flights resumed. Simple immediate cause and effect, with no complicated interpretations required to confuse the illiterati.

The author pegged this effect as the reason why climate models, which don't factor in pollution-based albedo, are predicting higher warming than has actually been observed, bad as that is. He said that without this higher albedo, actual warming would be twice what it is, which would then bring the models and reality into correlation.

A primary source of the increased albedo is Chinese air pollution particulates. So, we have the great irony that, as China cleans up its act and pollutes less, and despite lowered CO2 releases, the global warming trend is actually going to accelerate.
unrealone1
1 / 5 (4) Jan 13, 2016
How do Ice Sheets melt when the surface temp is Minus 20?
Volcanic activity!
EnricM
3.7 / 5 (3) Jan 13, 2016
How do Ice Sheets melt when the surface temp is Minus 20?
Volcanic activity!


Don't forget the Secret UFO base of SPECTRA!
runrig
4.3 / 5 (3) Jan 13, 2016
How do Ice Sheets melt when the surface temp is Minus 20?
Volcanic activity!

Err, when the sun shines on it.
runrig
5 / 5 (4) Jan 13, 2016
It's more complicated than prior posters have allowed.

Yes, the absence of contrails (Ci cloud) will allow for a greater diurnal range.
High cloud warms via the GHE (Low cloud cools via albedo).
But the timing and duration of them is very important.
Long lived contrails (formed in moist air and so inhibited from evaporation) are what are implicated here.
Those contrails formed at night would warm, whilst during the day cool.
Maybe the global average net effect is near zero?
..... but they add CO2 to the higher trop.

http://www.natura...ing.html
Scroofinator
not rated yet Jan 13, 2016
Let's not forget about low level cloud formation due to GCRs.
classicplastic
5 / 5 (1) Jan 13, 2016
Indeed, it's more complicated. Jet engine condensation trails are temporary and must be continually renewed to have even a local region impact.

Not factored in the referred article is the pollution particulates in the exhaust. These particles form the nuclei around which air humidity coalesces to create water droplets that become persistent high-albedo clouds. That's a very different thing and the only way to stop the effect would be electric airplanes, the technology of which Elon Musk hasn't quite perfected. However, on a global scale, they probably don't much matter.

But, contrails are just the canary in the coal mine, pointing to the deeper subject of anthropgenic albedo. The particulates from Asian fires and pollution cross the entire north Pacific ocean. Good graphic: http://www.phisic...res).jpg

So, Asian pollution is significantly mitigating global temp rises. I find that ironic.
SamB
3 / 5 (2) Jan 14, 2016
My wife and I had noticed the same effect here in Vancouver. When ever it was cloudy it was always a few degrees warmer. We did not know this was an unknown effect. Too bad we had not published our findings at the time. We would be famous!

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