We need some Symptomatic Relief

Ken Caldeira is an atmospheric scientist at the Carnegie Institution for Science’s Department of Global Ecology at Stanford University.

When thinking about the ethics of solar geoengineering, I like to use a medical analogy. Consider this: Should scientists who want to reduce the incidence of disease study ways to provide symptomatic relief, even if that relief does nothing to reduce disease? Should medical researchers who are concerned about finding a cure for cancer study how morphine and other painkillers might provide pain relief to suffering patients? Presumably, research into such pain relief draws away resources that could be used to better understand the root causes of cancer. Conceivably, such research could even increase the prevalence of cancer. By making the cancerous consequences of smoking less painful, this research could take away some incentive to quit smoking.

Geoengineering, it seems to me, is very similar. Planetary manipulation of the atmosphere to blunt the worst effects of global warming won’t address the root causes of climate change. But it might someday be able to alleviate suffering for hundreds of millions of people – and that is reason enough to study it for possible deployment.

The basic idea behind solar geoengineering is to counteract the warming influence of greenhouse gases by diminishing the amount of sunlight absorbed by Earth. When I first seriously considered the idea of solar geoengineering about 15 years ago, I thought the idea was loony. Greenhouse gases absorb energy day and night, in winter and summer, at the equator and the poles; whereas sunlight is only in daytime, and there is more in the summer than the winter, more at the equator than the poles. More of one is not going to be perfectly compensated by less of the other. So my research partners and I were surprised when the climate model we used showed a relatively high degree of compensation both regionally and seasonally.

But we still had other concerns. How, for example, would sunlight reduction affect plant growth and crop productivity? Once again, we were surprised to find evidence indicating that crop productivity would be higher in a geoengineered, high-CO₂ world than in a high-CO₂ world without solar geoengineering. Many crops in the tropics are already suffering from heat stress, and global warming will only make the problem worse. In our models, solar geoengineering reduces this heat stress, resulting in increased crop productivity, especially in the tropics.

Beyond the geophysical concerns lie geopolitical ones. Since solar geoengineering will, like other causes of climate change, affect everybody, everybody should be involved in the decision-making. Unfortunately, there is no global democratic institution (including the UN) in which everyone’s voice is heard. So who will decide when it’s time to deploy a solar geoengineering system? And what if others disagree?

Like trial medications, solar geoengineering may have awful side effects that would make it unusable to prevent or alleviate suffering. There is also the risk of addiction: If, once in place for a while, solar geoengineering were suddenly to be terminated, the planet would warm rapidly. We would be hooked on our thermostat.

We don’t know what the unanticipated side effects will be – which is why we need a research program to study it more fully.

Geoengineering concepts have been tested by nature. In 1991, a huge volcano in the Philippines called Mt. Pinatubo exploded, ejecting millions of tons of sulfur into the stratosphere. The sulfate particles that were produced deflected about 2 percent of sunlight away from Earth. The next year, Earth cooled by about one degree Fahrenheit (about a half of a degree Celsius). Based on the Mt. Pinatubo eruption, it is estimated that a single hose the diameter of a fire hose could carry more than enough material to offset all of the global average temperature increase expected this century. A small fleet of planes spraying sulfur into the stratosphere (costing only a few billions of dollars per year) could be enough to keep global average temperatures from rising.

However, Mt. Pinatubo also gives cause for concern. In 1992, the year after the Mt. Pinatubo eruption, the Amazon and Ganges rivers had the lowest flow ever recorded. Our models suggest that solar geoengineering might be able to offset about 90 percent of regional and seasonal CO₂-induced temperature changes but only about 70 percent of CO₂-induced changes to precipitation. Also, solar geoengineering obviously does not offset any of the CO₂-induced ocean acidification that is likely to harm marine ecosystems.

Global warming is an environmental cancer primarily caused by CO₂ emissions from our energy system. We know that the best thing to do is to address the root cause of this cancer. Indeed, most of my personal political activity is aimed toward this goal.

However, greenhouse gas concentrations continue to rise and the prospect is for the planet to get hotter and hotter. Because of lags involving changes in greenhouse gas emissions rates, atmospheric concentrations, and global temperatures, it is highly unlikely that emissions reductions could cause Earth to start cooling this century.

Let’s say climate change proves to be catastrophic and that heat stress causes widespread crop failures and famine in the tropics. If heat-induced starvation were to become prevalent in Africa or Asia, solar geoengineering is the only thing people could do to cause the planet to start cooling within years.

Solar geoengineering offers the hope of partial symptomatic relief. Of course, it is better to address the root cause of the problem, but cancer patients are glad that there has been research into painkillers. Nobody wants to be a morphine addict, but were I attacked by aggressive and painful cancer, I might decide to become one.

Nobody wants to deploy a solar geoengineering system, but on a hot, high-CO₂ world, it is possible that solar geoengineering might be the less-bad alternative. We would be remiss if we did not explore this possibility.