Geoengineering could stop global warming but carries big risks

Using radical techniques to "engineer" Earth's climate by blocking sunlight could cool Earth but presents great risks that could well worsen global warming should they fail or be discontinued, reports a new study published in the June 4 early online edition of The Proceedings of the National Academy of Sciences.

Using computer simulations to model the impact of proposed experiments using a solar filter to block sunlight instead of reducing greenhouse gas emissions, an international team of scientists conclude that geoengineering a risky strategy.

"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 co-author Ken Caldeira of the Carnegie Institution's Department of Global Ecology. "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."

Photo by Rhett A. Butler

Scientists have put forward several proposals to reduce the amount of solar radiation that reaches the planet's surface, including the use of light-reflecting sulfate particles in the atmosphere and installing mirrors in orbit around the planet.

The PNAS study shows that geoengineering schemes, even under a scenario of increasing emissions, could cool Earth within a few decades to pre-Industrial Revolution levels, but that failure of the system would result in "a catastrophic, decade-long spike in global temperatures... with rates of warming 20 times greater than we are experiencing today" as carbon sequestered in plants and soils would be quickly released into the atmosphere."

"If we become addicted to a planetary sunshade, we could experience a painful withdrawal if our fix was suddenly cut off," said Caldeira. "This needs to be taken into consideration if we ever think seriously about implementing a geoengineering strategy."

Caldeira and lead author Damon Matthews of Concordia University in Montreal say that their models also show geoengineering would affect global rainfall patterns, with lower levels of precipitation over tropical forests. In their models run with no simulated geoengineering, warmer temperatures resulted in more rainfall over the oceans and less over tropical forests

"Many people argue that we need to prevent climate change. Others argue that we need to keep emitting greenhouse gases," Caldeira said. "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."

Caldeira said that proposed geoengineering schemes need to be better understood before they are implemented but that the quick-acting nature of the projects mean that can put off geoengineering decisions until they become absolutely necessary.

"I hope I never need a parachute, but if my plane is going down in flames, I sure hope I have a parachute handy," Caldeira said. "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.