Ken Caldeira, of Stanford's Carnegie Institution, and H.Damon Matthews, of Concordia University in Montreal, Canada, specifically examined what might happen if a solar filter was put into place by using a computer model that simulated a global decrease in solar radiation. The authors assumed in their model that greenhouse gas emissions would continue their steady increase along projected trends for the remainder of the century.
"Given current political and economic trends, it is easy to become pessimistic about the prospect that needed cuts in carbon dioxide emissions will come soon enough or be deep enough to avoid irreversibly damaging our climate," said Caldeira. "If we want to consider more dramatic options, such as deliberately altering the Earth's climate, it's important to understand how these strategies might play out."While the model predicted that the geoengineering system could drastically cool off the planet within a few decades even in the face of rapidly increasing emissions, it also seemed to suggest that were the program to fail or be cancelled for any reason, a huge decade-long rise in global temperatures at rates far outpacing the current ones (up to 20 times greater) could occur. Another worrisome consequence of deploying this system would be a large decrease in global rainfall patterns.
"If we become addicted to a planetary sunshade, we could experience a painful withdrawal if our fix was suddenly cut off," Caldeira said. "This needs to be taken into consideration if we ever think seriously about implementing a geoengineering strategy ... Many people argue that we need to prevent climate change. Others argue that we need to keep emitting greenhouse gases. Geoengineering schemes have been proposed as a cheap fix that could let us have our cake and eat it, too. But geoengineering schemes are not well understood. Our study shows that planet-sized geoengineering means planet-sized risks."
Although Caldeira and Matthews aren't enthusiastic about the prospects for geoengineering, they don't think it should be taken off the table altogether. As Caldeira wrily noted: "I hope I never need a parachute, but if my plane is going down in flames, I sure hope I have a parachute handy. I hope we'll never need geoengineering schemes, but if a climate catastrophe occurs, I sure hope we will have thought through our options carefully."