Written By:Emma Websdale
Failure to curb greenhouse gas emissions could increase temperatures on Earth by 4oC by 2100, scientists warn, as a new study suggests that warming temperatures will mean fewer clouds to reflect sunlight back into space.
The research, led by Professor Steven Sherwood of Australia’s Centre for Excellence for Climate System Science at the University of New South Wales, suggests that as temperatures increase, fewer clouds will form. This will lead to more sunlight heating the Earth’s surface, driving temperatures up further.
The new climate model, which incorporates detailed accounts of cloud formation and changes, predicts that, without a reduction in greenhouse gas emissions, the planet will warm a minimum of 4oC by 2100. This is twice the increase that climate scientists have warned would be “catastrophic” if reached. Greenhouse gas emissions were relatively low until the start of the industrial age. Global temperature increases caused by these emissions are measured beginning from that point.
“This study breaks new ground twice: First, by identifying what is controlling the cloud changes and, second, by [discarding] the lowest estimates of future global warming in favor of the higher and more damaging estimates”, says Professor Sherwood, author of the study, to The Guardian.
He adds, “4oC would likely be catastrophic rather than simply dangerous. For example, it would make life difficult, if not impossible, in much of the tropics, and would guarantee the eventual melting of the Greenland ice sheet and some of the Antarctic ice sheet.”
The study, published in the journal Nature, reports that updrafts of water vapor can behave in two ways. Either the vapor can rise 15 kilometers (km) into the atmosphere to form high clouds that produce heavy rainfalls, or it can rise just a few kilometers before returning to the surface, without having formed any rain clouds. When the latter happens, overall cloud cover is reduced, as the updrafts draw water vapor away from higher elevations in a process called convective mixing. Cloud- and climate-modeling based on continued greenhouse gas emissions predict significant temperature increases.
“Climate sceptics like to criticize climate models for getting things wrong, and we are the first to admit [the models] are not perfect”, says Sherwood. “But what we are finding is that the mistakes are being made by the models [that] predict less warming, not those that predict more.”
Continued greenhouse gas emissions have also been projected to increase the number of people at risk of water scarcity by 40%. According to an international scientific research project known as the Inter-Sectoral Impact Model Intercomparison Project, one in 10 people will suffer from absolute water scarcity if temperatures on Earth increase 3oC (3.6oF) above pre-industrial levels.