Scientists Theorize Global Sunblock Could Lessen Warming

12 October 2012

If a method to brighten clouds can be devised, some scientists theorize the technique might help offset global warming.

Blocking the sunlight that reaches Earth might be another means to lessen the effects of climate change, some U.S. scientists theorize.

Scientists backed by the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL) are testing the idea with computer projections on future climate change.

“It’s a what-if scenario analysis,” said Steven Smith with the Joint Global Change Research Institute, supported by PNNL. “The conditions under which policymakers might want to manage the amount of sun reaching Earth depends on how sensitive the climate is to atmospheric greenhouse gases, and we just don’t know that yet.”

Scientists gauge climate sensitivity by measuring how many degrees the atmosphere warms as the concentration of carbon dioxide (CO2) increases. If the climate warms 3 degrees Celsius when CO2 doubles, Smith calls that a medium sensitivity, which would probably not merit attempts to block sunlight.

“It’s less likely we’d need solar radiation management at all,” he said in a PNNL press release. If a doubling of CO2 caused a greater temperature increase, 4.5 degrees C for instance, Smith said blocking sunlight would become a stronger option.

“We’re going to need to use solar radiation management if we want to limit temperature changes,” with a greater level of climate sensitivity, Smith said.

The reduction of greenhouse gas emissions, which trap heat in the atmosphere and stop their venting into space, remains a priority even if a reasonable method of managing solar radiation is devised.

“Solar radiation management doesn’t eliminate the need to reduce emissions,” Smith said. “We do not want to dim sunlight over the long term — that doesn’t address the root cause of the problem and might also have negative regional effects. This study shows that the same conditions that would call for solar radiation management also require substantial emission reductions in order to meet the climate goals set by the world community,” said Smith.

Besides, if solar radiation management and emissions reductions are both employed, the degree of sun-blocking necessary would be lessened, Smith said.

“Much of the current research has examined solar radiation management that is used as the sole means of offsetting a doubling of carbon dioxide concentrations,” Smith said. “What we showed is that when coupled with emissions reductions, only a fraction of that amount of ‘solar dimming’ will be needed. This means that potential adverse impacts would be that much lower.”

What those impacts could be is not well understood at this point, so this entire proposition is still in the research phase, Smith said. The potential methods to employ solar radiation management might include shading the Earth from the sun’s heat by brightening clouds, inducing the atmospheric cooling caused by volcanic eruptions or putting mirrors into space to deflect sunlight from reaching the Earth.