As scientists, with some reluctance, begin to study the idea of “geoengineering” the planet to slow or halt global warming, they are finding that any such program would quite likely have a complex array of effects, not all of them to humanity’s benefit
Laborers in Suchate Garh, India, near the border with Pakistan, planting rice seedlings. European Pressphoto Agency
In a paper released on Sunday by the journal Nature Climate Change, four California researchers used computer analysis to test the idea of managing incoming sunlight and predicted what that would do to crop yields. As an example of the strategies that might be employed, some sunlight could be deflected away from the earth by using planes or rockets to scatter sulfur compounds into the upper atmosphere on a routine basis, mimicking the effect of big volcanic eruptions. It is a potential response to global warming so cheap that it fascinates even some groups that have tried to block action on reining in carbon dioxide emissions.
Fears have long been expressed, however, that while a strategy like this might slow the overall warming, it could wreak havoc on global food security by altering rainfall patterns and other aspects of climate. Particular concern centers on the effects that such a strategy might have on the Asian monsoon, the source of water for crops that feed billions of people. The monsoon is driven by heating over land from strong sunshine in the summertime.
The new work, led by Julia Pongrantz of the Carnegie Institution for Science, found the opposite of these longstanding fears: managing incoming sunlight would probably benefit crop yields over all. The reason is that the technique would limit some of the damaging climate changes that are expected to hurt yields, like excessive temperatures in the growing season, but would nonetheless allow plants to benefit from higher levels of carbon dioxide in the atmosphere. The latter are rising, of course, because of fossil-fuel burning and are the main reason for global warming in the first place, but extra carbon dioxide does act as a kind of plant fertilizer.
The sunlight-limiting strategy would indeed weaken the Asian monsoon, the paper found, but not enough to offset the other benefits of the approach.
Despite their findings, the researchers suggested that much more work would be needed to understand the likely effects of a sunlight management strategy on agriculture. And they pointed out that the true consequences of such a program would be hard to foresee, producing regional winners and losers even if overall food output did increase. “The safest option to reduce the climate risks to global food security may be to reduce emissions of greenhouse gases,” they wrote.
In contrast to that work, another recent paper found potentially severe problems with using geoengineering to limit the effects of sea-level rise.
The ocean is rising as the planet warms and land ice melts, and scientists expect that rise to accelerate in the future — perhaps to the point of becoming a global crisis, given that many of the world’s major cities are in low-lying coastal regions. So a complex set of questions revolves around whether a geoengineering approach could slow the rise.
The new paper, published online on Jan. 8 by the journal Nature Climate Change, was led by Peter J. Irvine at the University of Bristol in Britain, working with collaborators at Pennsylvania State University. They found that a sunlight-limiting strategy would pose a potentially major conflict between managing air temperatures and managing sea level.
That is because air temperatures are believed to respond quickly to changes like reduced sunlight, whereas sea level — involving the slow melting of land ice and the gradual absorption of heat by the ocean, causing it to expand — responds much more slowly. In the language of the paper, “surface air temperatures react faster than sea levels to changes in earth’s radiative balance.”
That means that to halt sea-level rise quickly, a program of managing sunlight would have to be so aggressive that it would produce a rapid cooling of the planet’s air temperature — perhaps too fast for organisms and agriculture to adjust well. Conversely, a sunlight management program designed to produce a gentler reduction in the air temperature might fail to halt sea-level rise.
The scientists doubt that any optimal strategy could be found that would benefit all of humanity. Instead, they foresee potential conflicts between countries that care most about sea level (think of the Netherlands, for instance) and those that care most about temperature changes (think of tropical countries where higher temperatures would be a severe risk for agriculture).
The bottom line of these studies is that even as they dive into research questions on geoengineering, scientists are perhaps inevitably coming to the conclusion that we would be better off limiting our emissions now rather than handing future generations a mess that may not be at all easy to clean up.Read more... Sphere: Related Content