Nation

Global warming remedies studied by scientists

One may deflect solar radiation

WASHINGTON — The 1991 eruption of Mount Pinatubo, a volcano in the Philippines, blasted enough fine particles and sulfur dioxide gas into the atmosphere to envelop the Earth in a high-altitude cloud for the better part of two months.

When scientists checked in 1992, they determined that the cloud had deflected enough sunlight to cool the planet by about 1 degree.

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With the planet warming and the threat of long-term climate change looming, some experts are wondering whether the time may have come to deliberately attempt such ‘‘solar radiation management.’’

The idea is being investigated by, among others, the National Academy of Sciences, which is conducting research funded by the CIA, NASA, and the National Oceanic and Atmospheric Administration.

But even considering such an endeavor raises many practical, economical, political, and ethical questions, experts said, including what the affects on global and regional climates would be.

‘‘I’m not in favor of doing it today. I’m agnostic about whether we should ever do it,’’ said Alan Robock, a distinguished professor of environmental sciences at Rutgers University. ‘‘We don’t have enough information and, in any case, we don’t have the technology.’’

But Robock said additional research should be conducted despite concerns that determining the feasibility of such ‘‘geoengineering’’ might encourage a government or wealthy individual to try it, and could lessen efforts to curb greenhouse gases such as carbon dioxide.

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Mount Pinatubo’s eruption sent an estimated 20 million tons of sulfur dioxide and ash into the stratosphere, where the sulfur dioxide formed sulfate particles that reflected sunlight back into space.

Some believe this could be done effectively and at relatively low cost by injecting an aerosol of sulfur dioxide or some other gas into the atmosphere over a period of time, either from aircraft or missiles.

Ken Caldeira, a senior investigator for the Carnegie Institution for Science, told a congressional committee in 2009 that such methods are inexpensive, can be deployed quickly, and probably would cool the Earth effectively.

He stressed, however, that it is more important to address the root cause of global warming by reducing the production of greenhouse gases.

But Robock, in an interview, said the effort is ‘‘not feasible. No technology exists to do solar radiation management. There are no airplanes or hoses or missiles that exist to get sulfur up into the stratosphere.’’

A more limited variation of the idea is to spray sea salt into clouds over the ocean, probably from ships, to form more water droplets in the clouds and make them whiter, said Lynn Russell, a professor of atmospheric chemistry at the Scripps Institute of Oceanography, at the University of California at San Diego. The brighter clouds would reflect more sunlight.

But scientists are uncertain about how a major solar radiation management effort would affect rainfall, crop growth, and ocean life, among other things.

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