Geoengineering the clouds to reflect more light might not be so bad for the land underneath.
Concerns have been raised in the past regarding the effects of seeding clouds to make them more reflective and thereby reduce the radiation absorbed by the Earth. Researchers have believed that by doing so the global rainfall patterns could be shifted leading to reduced rainfall and increased water shortages.
However a new study by researchers from the Carnegie Institution suggests that the opposite is in fact true, and that altered atmospheric circulation under the scheme could in fact increase rains.
“Rain clouds, which have big droplets, tend to be grey and absorb sunlight, whereas clouds with smaller droplets tend to be white and fluffy and reflect more sunlight to space,” says co-author Ken Caldeira of the Carnegie Institution’s Department of Global Ecology. “In practice this could be done by shooting a fine spray of seawater high into the air, where the tiny salt particles would create condensation nucleii to form small cloud droplets.”
Caldeira and co-authors of the study used a computer simulation of the global climate system, and upped the atmospheric carbon dioxide concentrations to approximately twice that of present day. They reduced cloud droplets over the oceans, making the clouds more reflective, but left clouds over land unaltered.
What they found was that not only did the whitened clouds reflect more solar radiation and offset the warming effect of the high carbon dioxide levels but the model also showed that the oceanic clouds caused the land surface to become cooler and wetter on average.
The researchers believe that the increased land rain was caused by changes in air circulation out at sea, similar to the monsoonal patterns that determine rainfall in Asia. “Monsoons occur when air masses over land are warmer than air masses over the ocean, and this draws in cool, moist air from over the ocean which then drops rain over the land,” says Caldeira, which is exactly what the simulation did to the air over the oceans relative to the land.
Caldeira is quick to point out that despite the stunning results of the model it is not necessarily accurate of proposed geoengineering schemes. “In real life, there are only certain parts of the ocean in which you could make the cloud droplets smaller. An actual deployment would be much patchier than in our study, and the result would therefore be somewhat different. But our basic result calls into question previous assumptions about the impact of this geoengineering scheme. It merits further investigation.”
Source: Carnegie Institution
Image Source: Horia Varlan