December 12, 2013 – A new study appearing in the open access journal, Earth System Dynamics, analyzes energy balance in the atmosphere and its impact on the water cycle in a warming world. There is no doubt that a warming atmosphere will lead to increased evaporation. That’s how the atmosphere has always worked. So what happens when average temperatures rise globally? A lot more evaporation. The impact across the globe is variable. Some areas get drier. Others experience much more rainfall.
Now add changes to cloud cover and the amount of solar radiation striking the Earth’s surface. How is the water cycle impacted by the combination of the two? The new study, conducted by Axel Kleidon and Maik Renner of the Max Planck Institute for Biogeochemistry, located in Jena, Germany, tested a energy balance model to determine if a warming atmosphere without or with increased solar radiation creates different results. Lo and behold they found that the water cycle is both sensitive to atmospheric temperature as well as increased sunlight. In the case of warming without sunlight factored in evaporation grows by 2% per 1 Celsius (1.8 Fahrenheit) degree. In the case of increased sunlight evaporation grows by 3% per Celsius degree.
The analogy the scientists use is one of boiling a pot of water on the stove. You can do this with the lid on or off. Increase the heat with the lid off and you can boil the water. But put a lid on the pot and reduce the heat and the water still boils.
Now consider the Earth. Turn up the heat by increasing the temperature and evaporation increases. Add more sunlight and you enhance the energy flow with or without increasing the temperature. That means even greater evaporation.
One of the ideas for geo-engineering our atmosphere in light of increased CO2 has involved reflecting sunlight away from the Earth’s surface using a number of means. These have included putting mirrors up in space to deflect sunlight, or seeding the upper atmosphere to increase cloud cover. What the study suggests is changing the amount of sunlight reaching the surface by artificial means could have unintended consequences. After all one of the hypotheses to explain recurrent Ice Ages here on Earth correlates them to changes in Earth’s orbit, axial inclination and, therefore, the amount of sunlight reaching the planet’s surface.