A Limestone Sunshade Could Be a Risky Way to Cool the Planet

  The idea of geoengineering a solution to climate change has been discussed for decades, and now a new study proposes a plan that would cool the planet while repairing a hole in the ozone layer at the same time.

The trick: using calcite particles injected high into the stratosphere to reflect sunlight back into space, according to the study by a group from Harvard University published today in the journal Proceedings of the National Academy of Sciences.

While scientists say geoengineering is not a substitute for cutting emissions of heat-trapping greenhouse gases, they say that more research is needed on geoengineering as a possible additional measure to help the planet.

  “My view is that solar reengineering is a supplement, and in the end we still have to cut emissions,” said David Keith, professor of applied physics and public policy at Harvard and author of the new paper.

“But cutting emissions doesn’t cut the risk. A combination might to a better job.”

Keith says that a lot more research is needed at some of the possible side effects of putting calcite, which is abundant in limestone, into the atmosphere. The study uses computer models to see possible effects of spraying small calcite particles about 12 to 15 miles above the Earth’s surface in a region about 30 degrees north and south of the equator. That would cover most of the world’s tropical forests and oceans.