As Earth’s climate continues to warm, some scientists are looking at doing more than simply reducing humanity’s outpouring of greenhouse gases into the atmosphere by devising ways to actively cool the planet back to temperatures that our civilization is comfortable with. One of the proposed techniques would be to spray massive amounts of sulphur dioxide into the atmosphere to create a cloud layer that would reflect a portion of the Sun’s rays back into space, emulating the cooling effect that the gases from a large volcanic eruption would have. But a new study has found that while this practice of geoengineering would be effective for its intended purpose, we would be obligated to wind the program down gradually, as the consequences for an abrupt end to the effort would be more catastrophic than doing nothing at all to begin with.

"Rapid warming after stopping geoengineering would be a huge threat to the natural environment and biodiversity," warns study co-author Alan Robock, with the Department of Environmental Sciences at Rutgers University-New Brunswick. "If geoengineering ever stopped abruptly, it would be devastating, so you would have to be sure that it could be stopped gradually, and it is easy to think of scenarios that would prevent that. Imagine large droughts or floods around the world that could be blamed on geoengineering, and demands that it stop. Can we ever risk that?"

The study simulated the effects of spraying sulphur dioxide (SO2) at high altitudes to create a reflective cloud layer that would bounce a portion of solar radiation back into space. A massive amount of the chemical would need to be sprayed, to the tune of five million tons per year–every year–roughly the equivalent of one-quarter of the amount of SO2 ejected by the Philippines’ Mount Pinatubo during its 1991 eruption. After fifty years, the reflective could cover would drop the Earth’s temperature by one degree Celsius, roughly the same amount that has been packed onto the thermometer since the start of the industrial revolution.

But the simulation showed that stopping the program suddenly would have dire consequences, with global temperatures rebounding upward dramatically, 10 times faster than if geoengineering efforts hadn’t been undertaken to begin with. Between the sudden blast of heat and the dramatic changes in precipitation resulting from the temperature increase, the researchers found that numerous species would be unable to effectively relocate to areas with conditions favorable to their survival in time.

"In many cases, you’d have to go one direction to find the same temperature but a different direction to find the same precipitation," Robock explains. "Plants, of course, can’t move reasonably at all. Some animals can move and some can’t."

"We really need to look in a lot more detail at the impact on specific organisms and how they might adapt if geoengineering stops suddenly," Robock concludes. 

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