Blocking Sunlight To Reduce Global Warming Could Be Devastating For Crops


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockAug 9 2018, 21:42 UTC

One proposal for solar geoengineering is to inject sulfate aerosols into the atmosphere, similar to what happens after large volcanic eruptions, thus reducing sunlight and global temperatures. Stephen McNally and Hulda Nelson, UC Berkeley

Political ineptitude and laziness, combined with irresponsible capitalism, takes us every day closer to a world of higher temperatures and more extreme weather. Solutions to reduce our impact require drastic reductions in carbon emissions and investments, but they don’t seem to be happening. Desperate times call for desperate measures, and some researchers have looked into ambitious geoengineering projects such as blocking sunlight. However, the latest results don't look promising.

One of the ideas to cool down our planet sees the injection of particles into the atmosphere that can reduce sunlight and thus reduce heating in the lower atmosphere. While this might seem like an evil villain plan, volcanos do that naturally, and the work published in Nature aims to quantify the effect of such an enterprise on agriculture. While it might be effective at reducing temperatures, crops will also suffer greatly if sunlight is reduced in such a way.  


"Shading the planet keeps things cooler, which helps crops grow better. But plants also need sunlight to grow, so blocking sunlight can affect growth. For agriculture, the unintended impacts of solar geoengineering are equal in magnitude to the benefits," lead author Jonathan Proctor, a UC Berkeley doctoral candidate, said in a statement. "It's a bit like performing an experimental surgery; the side-effects of treatment appear to be as bad as the illness."

The team used the effects of the volcanic eruption that inspired this solar geoengineering approach to quantify some of the effects. They estimated the yield of maize, soy, rice, and wheat crops after the eruptions of El Chichón in 1982 and Mount Pinatubo in 1991. The Pinatubo eruption injected about 20 million tons of sulfur dioxide into the atmosphere, reducing sunlight by about 2.5 percent and dropping average global temperatures by about 0.5°C (nearly 1°F).

The researchers were surprised that the modeled yields for crops were negative after the injection of sulfate aerosols were considered. Protecting crops from heat damage with this approach would not have any benefits.


"Unknown unknowns make everybody nervous when it comes to global policies, as they should," said Solomon Hsiang, co-lead author of the study also at UC Berkeley. "The problem in figuring out the consequences of solar geoengineering is that we can't do a planetary-scale experiment without actually deploying the technology. The breakthrough here was realizing that we could learn something by studying the effects of giant volcanic eruptions that geoengineering tries to copy."

Despite this negative result, the team doesn’t think that we should write off the solar engineering model just yet. Their approach could be used to investigate the potential effects on human health and ecosystem function and see if it has any benefits that outweigh the costs.

Employing such a method would require a lot of work. The lifetime of these aerosols is limited and much shorter than greenhouse gases. When they are depleted, the global temperatures will begin to rise again. We would still have to drastically reduce carbon dioxide emissions to tackle global warming.