Climate simulations: Researchers want to have solved clouds puzzles

Clouds are the large uncertainty in climate simulations: they largely determine how much greenhouse gases will warm the Earth - and yet their influence is extremely difficult to calculate. Now researchers want to have solved the mystery.

The concentration of greenhouse gases in the atmosphere is increasing rapidly . To pre-industrial times , it stood at 280 parts per million (parts per million , ppm ) , now she has at times been exceeded 400 ppm. Less clear , however, is how strong the greenhouse gases are warming the earth.

Experts speak of climate sensitivity : It says how big the heating fails when the GHG concentration doubled to 560 ppm. According to the latest report of the UN IPCC would be a warming between 1.5 and 4.5 degrees expected. What is the value will turn out exactly determine in large part the clouds - and it's them are particularly difficult to calculate .
But now wants to have solved the mystery a Australian- French research team . And the results have now been published in the journal "Nature" does not bode well . The effect of clouds on the warming has been underestimated , the scientists write to Steven Sherwood of the Australian University of New South Wales. The doubling of the carbon dioxide will heat the atmosphere in the global average of not 1.5 to 4.5 , but by 3 to 5 degrees .

Eight degrees of warming by the year 2200 ?

If this is true , would be an optimist to hope continue to be able to still somehow limit global warming to two degrees. Beyond that, scientists expect potentially disastrous consequences in some regions of the world . Secondly, the results would mean of Sherwood's team that the Earth is warming at least four degrees by the year 2100 . Because the doubling of the CO2 concentration to 560 ppm of the IPCC already expected in approximately 40 to 70 years - depending on how to develop the global emissions.

The key of the new calculation is according to the researchers in the effect of global warming on the formation of clouds . Observations have shown that higher temperatures led over the tropical sea in a weaker cloud formation at low altitude . In this way, more sunlight reaching the surface and lead to an even stronger warming.

The mechanism behind this is the mixing of the water vapor resulting from evaporation. In a warmer climate , write Sherwood and his colleagues , will the water vapor in the clouds at a height of two to three kilometers and higher layers of the atmosphere more mixed . This leads to the fact that the lower layers of moisture will be withdrawn. Thus there would arise less clouds, could reflect sunlight back into space .

The scientists have analyzed and found that many of them the steam process is not sufficiently taken into account and so predicting too low a warming 43 climate models .

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