SOLAR TODAY - June 2009

tackling climate change
Plan B for Climate Change
It’s called geoengineering , but don’t tell anybody!
By ChuCk kutsCher

Chuck Kutscher is a principal engineer and manager of the Thermal Systems Group at the National Renewable Energy Laboratory. He is a past ASES chair and was chair of the SOLAR 2006 conference, which resulted in the ASES report, “ Tackling Climate Change in the U.S.” (Free download at ases.org/ climatechange.) He taught a course at the University of Colorado entitled “Climate Change Solutions.”

The opinions expressed here are solely those of the author.

As climate change accelerates, some scientists are the lower atmosphere, enhancing low-altitude cloud cover
beginning to discuss a radical approach that many over the oceans to reflect more sunlight. The ships would
considered taboo: geoengineering. Geoengineer- be wind powered, making this a green energy technology!
ing has been defined as “planetary scale environmental engi- With an estimated price tag of $3 billion, this project would
neering aimed at counteracting undesired side effects of human be a relative bargain. And because the effects of water-
activities.” In other words, to make up for the damage that droplet injection are short lived, this experiment could be
our greenhouse gas emissions are causing to the planet, we quickly halted if it brought about unsavory consequences,
will make other large-scale planetary changes in an attempt like large changes in rainfall patterns.
to compensate. If that sounds scary, well, it should. Because all of these options reduce solar radiation, the
Most geoengineering ideas involve schemes that negative implications for solar energy technologies are obvi-
decrease the amount of sunlight reaching the Earth's sur- ous. Concentrating solar power plants like SEGS, which rely
face to counterbalance global warming. The most popular on direct solar radiation, would be especially hard hit. But
concept has its origin in volcanoes. When Mount Pina- that's the least of the problems. For one thing, any method
tubo in the Philippines erupted in 1991, it injected an that reduces sunlight does nothing to reduce the buildup
estimated 15 million metric tons of sulfur dioxide into the of carbon dioxide in the atmosphere and the oceans. CO
2
stratosphere. The resulting solar dimming persisted into will continue to dissolve in the oceans, making them more
1992, and its effects were felt
around the globe. There was
even a large drop in the output
of the solar electric generating
stations (SEGS), a group of
parabolic trough plants in the

Mojave Desert, and the average temperature in the northern hemisphere dropped by about 1˚F (0.5˚C). Taking a cue from volcanoes, we merely need to inject up to 5 million tons per year of sulfur dioxide into the stratosphere to reduce solar radiation by 3 percent. The estimated cost is $25 billion to $50 billion per year. While it would reduce incoming solar

USGS

radiation, it could also damage the eruption of Mount Pinatubo on June 12, 1991, sent huge quantities of sulfur dioxide the ozone layer and affect pre- into the stratosphere that caused a 1˚ F drop in the average temperature of the northern cipitation patterns around the hemisphere. One geoengineering approach attempts to mimic this process. world. Oh, and it would increase acid rain.

Then there's the idea of putting a trillion computer-con-trolled, two-foot-diameter mirrors a million miles out in space between the sun and the Earth to reduce the amount of sunlight reaching us. All we have to do is pay for the mirrors and the launch costs, estimated to be $5 trillion. (Yes, that’s trillion with a “t.”)

Perhaps the least onerous of these shading concepts is the idea of maintaining a fleet of 1,500 ships that would continuously spray microscopic droplets of salt water into

18 June 2009 SOLAR TODAY solartoday.org

acidic and killing coral. As the coral reefs die, this will have untold consequences on the ocean's food chain, to say nothing of the island and coastal communities that rely on the reefs for storm protection, fisheries and tourism.

And then there is the little problem of what happens if any of these methods suddenly fails. What if the computers on those mirrors stop working? Or what if a war, a worldwide epidemic or a global economic depression causes us to stop injecting sulfur dioxide or sea spray into the atmosphere? Then all that carbon dioxide that was building up