In light of society’s failure to take any concerted actions to deal with global warming, two prominent atmospheric scientists — Paul Crutzen, who won a Nobel Prize in chemistry in 1995, and Tom Wigley, a senior scientist at the National Center for Atmospheric Research — published papers in 2006 suggesting that society should consider using geoengineering to solve the problem of global warming. Such suggestions are not new. The concept of geoengineering — deliberately introducing some technology to modify Earth’s environment — has been bandied about since at least 1960. Over the years, proposals have included everything from carbon sequestration to ocean fertilization to damming the oceans. Crutzen and Wigley argued that geoengineering schemes, if done continuously, could reduce global warming enough to buy society time to address mitigation. However, geoengineering is not the answer. And in fact, such measures create more problems than they solve.
In particular, Crutzen and Wigley focused on blocking incoming solar radiation, an idea that has generated much interest in the press and the scientific community. Nature offers an example of how to do this. Volcanic eruptions cool the climate for up to a couple of years by injecting precursors to sulfate aerosol particles into the stratosphere that block incoming sunlight. It is true that volcanic eruptions cool the climate, but their effects are not innocuous, and should serve as a warning to society to be wary of such geoengineering “solutions.” The particles from volcanic eruptions cause ozone depletion. And reducing solar radiation also reduces evaporation and hence precipitation — more than warming by greenhouse gases increases precipitation. So balancing the temperature with aerosols actually reduces global average precipitation.
Furthermore, the cooling is not uniform: In the Northern Hemisphere, aerosols cause more cooling over the Eurasian continent than over the oceans in the summer, thus reducing the strength of the Asian summer monsoon, which provides rain to grow the food supply for billions of people. These rain reductions have been observed after major volcanic eruptions, but they only last a year or two, and do not have long-lasting consequences. With continuous geoengineering, however, these effects would persist for years.
There are other reasons to be concerned about “solar radiation management.” There would be less solar radiation for solar power, especially for systems requiring direct radiation. And by not dealing directly with greenhouse gas emissions, carbon dioxide would continue to accumulate in the oceans, causing more ocean acidification.
Furthermore, if such geoengineering were to stop precipitously — and one could imagine this happening as a result of failures of technology, societal will or capability — warming would be exceptionally rapid. The rate of climate change is one of the most important disrupting factors.
Even if geoengineering worked, whose hand will be on the thermostat? It’s unlikely that the world could agree on an optimal climate. What if Russia wanted it a couple degrees warmer and India a couple degrees cooler? Should global climate be reset to the pre-Industrial value or kept constant at today’s climate? Would it be possible to tailor the climate of each region of the planet independently without affecting the others? Current understanding says no, so if we proceed with geoengineering, will we be producing future climate wars?
One of the most important concerns is that schemes perceived to work will lessen the incentive to mitigate greenhouse gas emissions. Solving the global warming problem is not as much a technical problem as a political one. Currently the U.S. government gives multibillion-dollar subsidies to the coal, oil, gas and nuclear industries, and gives little support to alternative energy sources like solar and wind power. Switch that and see how fast the situation changes.
The sooner we as a society give our scientists and engineers the resources necessary to address this problem — in the same vein as the Apollo project or the Manhattan project — the sooner we can develop the technology needed to use energy more efficiently and produce the renewable energy we need.
Geoengineering is not a panacea and we cannot delay the search for real solutions in the hope that geoengineering will save us. Yes, geoengineering research should continue: We need to better understand the efficacy and potential problems related to such measures. However, at the same time, we need a massive research program addressed toward mitigation. We may at some time need to consider some sort of geoengineering as an emergency measure, but we have to know how well it would work and the dangers involved. And the faster we work toward mitigation, the less likely we are to need geoengineering.
Robock is with the Department of Environmental Sciences at Rutgers University in New Brunswick, N.J. E-mail: firstname.lastname@example.org.
Climate engineering is not a panacea for the ills caused by greenhouse gas emissions, but perhaps while we take the necessary steps to radically transform our energy and transportation systems and establish improved stewardship of both land and ocean, it may be able to relieve some of the symptoms of global warming.
Carbon dioxide causes Earth to warm. But carbon dioxide also causes acidification of the ocean and affects the growth of land plants. One could imagine schemes to prevent Earth from absorbing some sunlight, thus offsetting some of the climate effects of carbon dioxide, but these proposals would not offset the chemical effects of carbon dioxide. Nobody would suppose that the climate offsetting would be ideal. Cuts in carbon dioxide emissions must come soon and they must be deep.
However, just as palliative medicine reduces the pain of an underlying disease, proposals to engineer the amount of sunlight absorbed by Earth could potentially serve as a painkiller. Of course, curing the disease is always the preferred path. But if our goal is to reduce suffering, we apply palliative care when the proposed cure is not having the intended effect.
The art of pain relief is not perfect. In some cases, palliative care fails to relieve all pain. But we do not deny a patient pain medication just because the medicine does not work perfectly. Palliative care may also come with negative side effects. In these cases, a cost-benefit analysis must be applied: Is the patient’s condition improved or worsened by the application of a painkiller?
The case of climate engineering is largely analogous. In general, analyses of proposed climate engineering schemes show that, if intelligently deployed, they can diminish the overall amount of climate change in most places. These schemes do not promise perfection, but they may offer a reduction in suffering.
As Alan Robock observes, one oft-cited example of climate engineering is effectively blocking out the sun, which will change both precipitation and temperatures around the world. We would have to go about this carefully, meticulously picking what effects we want. If we engineer the climate to return the global mean precipitation back to “normal,” there will be some residual warming. If we engineer the climate to bring the global mean temperature back to “normal,” there will be less precipitation. That is because there is less evaporation, due to less sunlight striking Earth’s surface. But less evaporation also means moister soils, causing the opposite effect of less precipitation. It is not clear which effect will “win out” under which conditions. Thoughtful climate engineering, however, may be able to bring climate closer to its “natural” state.
Robock also mentions the reduction in monsoonal circulation observed after a large volcanic eruption. With rapid cooling, the land cools more than the ocean due to its lower heat capacity. This cooling tends to cause air masses to sink over the land, setting up a preferred anti-monsoonal circulation. This result indicates that we would want to avoid rapid cooling when deploying a climate engineering system, which would likely be avoided in a prudent climate engineering deployment.
A common assumption that the investigation of climate engineering schemes will lead to complacency and even greater greenhouse gas emissions must be put to rest. When the general public and policymakers become aware of the desperate measures scientists are exploring to alleviate the suffering that climate change may cause, this should result in a reinvigorated effort to eliminate carbon dioxide emissions and obviate the need for palliative care.
We absolutely should be curing the disease and not simply treating the symptoms, but the cancer of carbon dioxide emissions seems to be metastasizing — evidence of the disease was once seen most clearly only in Europe and North America, but now China and India are also exhibiting malignant growth. Carbon dioxide emissions and atmospheric carbon dioxide concentrations are both growing more rapidly than foreseen just a few years ago. The trend in energy systems seems to be toward greater use of coal, the most abundant and carbon intensive fossil fuel available.
So, yes, we need to solve the difficult problem of achieving cooperation and self-sacrifice required to cure this carbon-induced disease. But when a disease is spreading as rapidly as this one is, it is not too soon to look to palliative care. As Robock points out, we need to do the research now so that we can make sure that we will not do more harm than good. Climate engineering will not be perfect, but who thought it would be?
Caldeira is with the Department of Global Ecology at Carnegie Institution in Stanford, Calif. E-mail: email@example.com.