Geoengineering: One Risk Versus Another

The Associated Press reported on a National Academy of Science meeting held in February of this year quoting several speakers from a panel recommending expanded research on geoengineering as a tool against climate change. The NAS's panel discussion highlighted a method of "solar forcing" that calls for the injection of sulfur-dioxide (SO2) into the atmosphere as a reflecting agent to counteract the warming effect of greenhouse gases. This technique has been proposed either as a way to continue our dependency on fossil fuels without warming the planet or as a last ditch effort to rescue humankind should we not find a way to significantly curb emissions before climate changes overwhelm us.

The idea of geoengineering the climate with SO2 aerosols has been in the pipeline for more than twenty years, primarily at the outer fringe of climate science. That we should see articles about SO2 infusion in the mainstream media today underscores something of climate change's real time immediacy and what we might be looking at if we don't do something about it. "If this is our Hail Mary," said Marcia McNutt, editor of the Journal of Science, "what a scary, scary place we are in." Intentionally cutting carbon emissions is a far more intelligence response than a Hail Mary.

Mount Pinatubo in the Philippines erupted several times in June of 1991. In total it produced ten cubic kilometers of volcanic debris, making it the second largest volcano of the 20th century and ten times larger than the 1980 eruption of Mount St. Helens. Along with the explosion of magma and ash, the eruption released 17 million tons of SO2, creating a global layer of sulfuric haze that remained in the stratosphere for three years. Because of the reflective qualities of sulfate gases, the amount of sunlight reaching the Earth's surface during those three years was reduced by five percent, leading to a decrease of .5-.6 degrees Celsius in surface air temperatures in the northern hemisphere and .4 degrees for the entire globe. These effects were judged so significant that climate scientists immediately began to study the event, wondering if intentionally injecting sulfates into the atmosphere could be a credible way to combat global warming.

Modifying the climate by any means is an extreme concept, both for the scale of the operation involved and the repercussions even slight changes can produce. The problem is complicated by the difficulty of testing the effectiveness of a geoengineering scheme in the field or in a lab. This has prompted climate scientists to turn to computer modeling.

Researchers Ken Caldeira and H. Damon Matthews at the Department of Global Ecology in Stanford, California did this eight years ago, using a computer to simulate the effects of intentionally reduced solar radiation (solar forcing) on the global climate system. Their results were published in the June 11, 2007 Proceedings of the National Academy of Sciences under the title "Transient Climate-Carbon Simulations of Planetary Geoengineering."

The Caldeira-Matthews' analysis involved eleven computer simulations run for the time period 1900 to 2100. All runs were based on a business as usual carbon emissions scenario which projected an increase of atmospheric carbon dioxide concentrations from 280 parts per million in 1900 to 880 parts per million in 2100.

One run contained no human initiated reduction of solar radiation. Four runs included geoengineered solar forcing begun in each of the years 2000, 2025, 2050, and 2075. Three runs included solar forcing begun in 2000 with an abrupt cessation of the geoengineering in 2025, 2050, and 2075.

The model showed that without any geoengineering Earth's surface air temperatures would increase an average of 3.5 degrees Celsius by 2100. When solar forcing was initiated in the year 2000, average air temperatures for the year 2100 remained very close to 1900 levels, actually decreasing .35 degrees Celsius in the tropical Pacific and increasing less than 1.0 degree in the Arctic.

In runs where solar forcing was initiated in 2025, 2050, or 2075, all surface air increases due to greenhouse gas effects were eliminated in less than 10 years. However, when the solar forcing was abruptly terminated, atmospheric temperatures climbed to where they would have been without the SO2 at a rate of 4 degrees Celsius per decade–twenty times the current rate of .02 degrees per decade. In other words, abrupt cessation creates a situation worse than what existed prior to the geoengineering.

The Caldeira-Matthews' computer simulations showed that intentionally decreasing solar radiation can counteract the effects of greenhouse gases, and that it works reasonably quickly. "Hence," wrote the two scientists, "there may be little cost to delaying the deployment of geoengineering strategies until such a time as 'dangerous' climate change is imminent." This somewhat sanguine remark is balanced by their worries about the impact of an abrupt geoengineering failure, the continued acidification of the oceans, and "unresolved concerns that geoengineering proposals involving sulfate aerosols may have negative consequences on stratospheric ozone levels."

The long and the short of it is this: monkeying around with a system as complex as a planet's atmosphere is just as foolhardy as unrestrained carbon emissions. Yes, geoengineering research will invariably increase in the years to come with who knows what breakthroughs, and, yes, the Caldeira-Matthews' computer simulation is only one model among many. Still, even at its best, geoengineering is like the worst of modern medicine; it treats the symptoms not the disease.

The warming of the globe is characterized by two particularly alarming positive feedback loops–loss of planetary ice mass increasingly diminishes the planet's ability to cool itself and melting permafrost in northern latitudes increasingly releases more methane as temperatures climb. (Methane is greenhouse gas twenty times more effective at trapping heat than CO2.) This means the warming trend comes on like a crescendo–the front edge of which we are only beginning to see. When this potential wildfire really gets going, geoengineering with sulfate aerosols could be used as a stop-gap, last resort. This is something–considering we may already have gone too far. In the end, however, we are simply weighing one risk against another: the unknown potentials of global warming versus the endgame gamble of geoengineering. Finding the political will, particularly in the United States, to significantly cut carbon emissions is a better answer. Otherwise we will find ourselves entering into a last-second, planetary-scale experiment that will turn something resembling B-grade science fiction into reality TV. Unfortunately, short of some unforeseen climate management solution, this is precisely the path we are on.

Click here for a more in depth review of Caldeira's and Matthew's work.