Clouds could explain how Snowball Earth thawed out

Nov 13, 2012
Credit: NASA

Glaciation events during the Neoproterozoic (524-to-1,000 million years ago) and Paleoproterozoic (1,600-to-2,500 million years ago) periods - events that spawned ice ages that persisted for millions of years at a time - may have seen glacier ice encircle the planet in a frosty planetary configuration known as a Snowball Earth.

Whether the planet could have existed in such a state, however, is a matter of considerable debate. An elevated planetary albedo, caused by the planet being covered in reflective snow and ice, would mean that a would reinforce itself. With no known mechanisms able to fully explain how the planet could have thawed out from such a state, some scientists suspect that Snowball Earth never happened.

However, using a series of global general circulation models, Abbot et al. find that the greenhouse potential of clouds, which had been overlooked in previous research, could explain how a Snowball Earth may have melted.

Previous modeling research found that to thaw out a glacier that covered the planet would require carbon dioxide to account for up to 20 percent of the atmosphere by volume. Paleogeochemical evidence, however, shows that carbon dioxide levels reached only 1 percent to 10 percent. The model used for the earlier research, the authors find, ignored the warming potential of clouds.

Clouds not only trap infrared radiation near Earth's surface, warming the planet, but also reflect , cooling the planet. In the modern climate, both effects are important. However, set against a planet encompassed in ice, clouds' reflectivity becomes less important, and the overall effect of clouds is to warm the planet.

By accounting for the heat-trapping effects of clouds, the authors find that the concentration required to drive deglaciation is 10-100 times lower than previous research suggested, a concentration that fits within observed levels.

Explore further: New study confirms water vapor as global warming amplifier

More information: Clouds and Snowball Earth Deglaciation, Geophysical Research Letters, doi: 10.1029/2012GL052861 , 2012

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RealityCheck
1 / 5 (5) Nov 13, 2012
One point has been overlooked. If pan-globe ice cover is achieved, the surface-reflection of daylight back up into the atmosphere would be like having a sun shining on most air from above AND below! So during daylight the moist air is too warm to condense into clouds even when 'supersaturated'. As moist air regions rotates towards the nightside of the planet, the moist air condenses into clouds which reflect back DOWN any latent heat IR radiated from surface/lower atmosphere. When again in daylight, these clouds would 'evaporate' to transparent moisture once more and not reflect away any daylight from above. Hence the cloud effect would then have bee more 'biased' than today's 'balanced' dynamics of condensing anytime conditions are right, day OR night. Just an observation given 'snowball earth' was ever to such a global coverage as alleged. Cheers!
jamesrm
not rated yet Nov 14, 2012
"Clouds would 'evaporate' to transparent moisture"

Transparent at what wavelengths?