I had to chuckle when I read the following press release on a study that found that global precipitation has not risen after all. Models and media reports wrong again!
Warm air can hold more water vapor than cold air. Does this mean that climate warming leads to more precipitation on average than it did a few decades ago? Dr. Marc Salzmann of the Institute for Meteorology at the University of Leipzig looked at this question. In a study he found that climate change so far has not had an impact on the average global precipitation amount. This could change by the end of this century. The meteorologist published his findings in “Science Advances”.
“The Arctic is melting, temperature and sea level are rising, and every year a new record is reached with CO2 in the atmosphere. Only the global average amount of precipitation has not changed measurably,” says Salzmann. Indeed precipitation has increased in some regions of the earth, but at the same time it has decreased in others. It is also known that as a consequence of climate change, there are heavy rainfalls more often. “With the worldwide average precipitation, however, neither computer models nor observations show significant changes,” he explains.
This is due to tiny particles called aerosols that float in the air and are created, for example, by sulfur dioxide. They have a cooling effect on the climate. But according to Salzmann, they do not suffice to offset the global temperature warming that is caused by greenhouse gases. Yet the affect of aerosols on precipitation has still been strong enough to offset the affect by greenhouse gases on the global average precipitation.
“My study shows that the global precipitation amount on average falls an estimated 3 to 4% per degree Celsius of cooling by aerosols, while the already known value for greenhouse gases is only 1.5 to 2% precipitation increase per degree of warming,” says the meteorologist. These different “hydrological sensitivities” is the reason why we can be thankful that the average precipitation amount has changed very little worldwide even though the global mean temperature has risen.
However for the future – already at the end of this century – Salzmann expects a significant increase in global precipitation amount. Because greenhouse gases stay in the atmosphere for a long time, the concentration rises even if emissions remain steady. Aerosol particles on the other hand get washed away by rain rather quickly.
Original in “Science Advances”: “Global warming without global mean precipitation increase?”