The Best Way to Shade the Earth
A new study of a proposed geoengineering technique to artificially shade the Earth shows that troublesome side effects could be minimized by injecting particles into the atmosphere from points on the planet farther away from the equator.
The results of one model simulation suggests that droughts, major rainstorms and more rapid polar ice melting might be reduced by changing the places and the frequency of injections.
The research on what scientists call SRM, or solar radiation management, took three months running a sophisticated global climate model on one of the world's fastest computers. It helped scientists identify potential changes to droughts and major rainstorms.
"We ran this 20 times to get a number of weather variations," said Simone Tilmes, an atmospheric chemist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo.
She explained that the results varied from earlier studies that simulated the release of aerosols made from sulfur dioxide at locations near the equator at altitudes in the atmosphere ranging from 12 to 15 miles. From there, they quickly get transported around the globe.
The earlier studies followed the path taken by the huge plume of soot, sulfur and other debris ejected from Mount Pinatubo, the Philippine volcano that exploded in June 1991, leaving a huge, water-filled crater.
The eruption shaded the Earth, dropping global average temperatures by almost 1 degree Fahrenheit (0.3 degree Celsius) between 1991 and 1993. Currently, scientists from several nations are working on studies to see if making continuous injections of aerosols might be able to produce a similar effect. The injections are usually done by aircraft.
The theory is that volcanic eruptions have repeatedly proved that shading happens without causing widespread disasters or major health problems.
Last year, Tilmes and a team of scientists set to work experimenting with a global climate model on a new supercomputer at a facility run by NCAR and the state of Wyoming in Cheyenne. They changed the injection points and used formulas to modify the annual amounts of injections as they simulated multiple shadowing efforts extending from 2020 to 2099.
They found that moving the injection points from the equator to points that were 15 degrees and 30 degrees in latitude north and south from the equator tended to reduce unwanted side effects in the weather. The result indicated better atmospheric mixing.
In all, they simulated 2,227 years of annual shading efforts.
"Nobody has ever done this using the complicated model as we did," said Tilmes. She said the next step would be a closer look at regional climate models to get a better sense of resulting weather patterns. She wants to see, for example, if a predicted drop in precipitation might come gradually or in the form of prolonged droughts.
The goal of the Paris Agreement, signed by 195 nations in 2015, is to keep global average temperature increases below 1.5 degrees Celsius above preindustrial levels. The puzzle that Tilmes and other scientists are trying to explore is whether that goal might be implemented, and how.
Average temperatures have already risen by 1 degree Celsius. That has led some scientists to believe that shading might be needed as an added effort to prevent more harmful warming effects in the coming decades. One of them is David Keith, a Harvard University physicist, who worries that the slow response of the climate to reduced emissions, plus the possibility of further damage from "feedbacks," such as the melting of the Arctic's permafrost, releasing more carbon dioxide, means that shading will be needed.
"There is a small but significant chance that the world will continue to warm for more than a century after emissions stop," he warned in a paper written last year.
Keith noted that economists have predicted that worldwide damage from hurricanes, prolonged droughts and other warming-influenced weather events could reach $1 trillion a year later this century. The cost of adding global shading to meet the Paris target would be a "few billion dollars per year," he estimated.
To some, the shading option remains new and controversial. But it has been repeatedly suggested in various U.S. administrations since the first climate change report arrived on President Lyndon Johnson's desk in 1965. Because increasing global warming would have its greatest impact on poorer countries and upon people who lack the money to move or adapt, "one can make a strong ethical case for research to explore the technology," Keith argued.
The Trump administration hasn't supported any organized U.S. research on shading, but Keith will help lead a group of Harvard scientists next year to launch a small, unmanned and privately financed balloon experiment in the stratosphere over Arizona. They want to see what aerosols will make the safest and most efficient reflectors of sunlight. The tests will include a plume of ice crystals, calcium carbonate and forms of sulfur that volcanos tend to erupt.
A group of scientists at the Institute for Advanced Sustainability Studies in Potsdam, Germany, recently took a look at another potential side effect of shading. It's called "termination shock." That is a scenario where nations start widespread global solar shading until some event, such as a war or a terrorist act, abruptly ends the effort.
Under the "termination shock theory," some assumed the result would be cataclysmic in the form of rapidly increasing temperatures. But the Potsdam study found there would be a lengthy "buffer period" of several weeks or months before an increase in warmth, long enough for a global system of aircraft and their bases to recover from a potential catastrophic event and resume injections of shading materials.
The Potsdam study estimated that a global injection system might cost an initial $50 billion to set up and then $12.5 billion to operate each year. The system would involve hundreds of aircraft, "most likely operating out of numerous airfields around the world." In case of a terrorist attack, it would be "relatively easy" to restart it after a disruption, the study said.
The idea of such an international protective effort may still seem unusual to some people, but Keith and other advocates point out that countries do forms of coordination on a daily basis in such areas as central banking, protection against infectious diseases and global air traffic control.
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.