Earth sunblock only needed if planet warms easily

Planet's sensitivity to greenhouse gases will determine how much shading could be needed to slow temperature rise.

An increasing number of scientists are studying ways to temporarily reduce the amount of sunlight reaching the earth to potentially stave off some of the worst effects of climate change.

Because these sunlight reduction methods would only temporarily reduce temperatures, do nothing for the health of the oceans and affect different regions unevenly, researchers do not see it as a permanent fix. Most theoretical studies have examined this strategy by itself, in the absence of looking at simultaneous attempts to reduce emissions.

Now, a new computer analysis of future climate change that considers emissions reductions together with sunlight reduction shows that such drastic steps to cool the earth would only be necessary if the planet heats up easily with added greenhouse gases. The analysis, reported in the journal Climatic Change, might help future policymakers plan for a changing climate.

The study by researchers at the Department of Energy's Pacific Northwest National Laboratory (PNNL) explored sunlight reduction methods, or solar radiation management, in a computer model that followed emissions' effect on climate. The analysis shows there is a fundamental connection between the need for emissions reductions and the potential need for some sort of solar dimming.

"It's a what-if scenario analysis," said Steven Smith with the Joint Global Change Research Institute in College Park, Md, a joint venture between PNNL and the University of Maryland. "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."