Save Lives and Keep Extreme Weather in Check by Cutting Smog, Soot, and CO2 Pollution

An important study published in Science last week shows that targeted measures to curb methane, black carbon, and carbon dioxide emissions would yield huge public health and environmental benefits. Pollution reductions from this strategy would prevent 700,000 to 4.7 million premature deaths each year, increase crop yields, and greatly reduce the risk of extreme climate disruption that lies beyond global warming of 2 degrees Celsius.

Drew Shindell of NASA and an international team of 23 coauthors made the most careful study to date of the global air quality improvements that could be achieved by systematically curbing emissions of methane (which increases ozone smog and traps heat) and black carbon (aka soot, which causes respiratory disease and absorbs solar energy). After initially screening about 400 pollution control measures, the team focused on 14 that showed the greatest promise of improving air quality and limiting climate change. Shindell and colleagues then analyzed the benefits of these measures in detail using global models that simulate both chemical and physical interactions to project changes in air quality and climate. Carbon dioxide emissions were based on the International Energy Agency’s scenario that stabilizes heat-trapping gas concentrations at the equivalent of 450 parts per million of CO2.

What kind of measures are we talking about? Mostly straightforward application of best practices, such as capturing, rather than venting, methane during coal, oil, and gas production and installing particle filters on diesel engines. More challenging measures include intermittent aeration of rice paddies and replacing traditional wood-burning cook stoves with cleaner versions or modern fuels. The full list is supplied in the Supporting Online Material (subscription required).

The black carbon reductions accounted for most of the projected lives saved based on the well-established link between breathing fine particles and respiratory disease. Both black carbon and methane reductions contribute about equally to the improved crop yields. Reductions in black carbon, methane and carbon dioxide are all needed to keep global warming below 2 degrees Celsius (see figure). Black carbon and methane reductions make the most difference in the near term because they are relatively short-lived in the atmosphere, whereas CO2 reductions must start now to limit long-term warming because CO2 can stay in the atmosphere for more than a century. The study is actually very conservative in that it did not attempt to estimate the additional lives that would be saved from improved nutrition due to increased crop yields nor from reduced extreme weather, such as heat waves and flooding, due to reduced climate change.

Predictably the usual suspects seized on the study to push their pre-existing agenda of arguing that trying to limit carbon dioxide pollution is a fool’s errand. John Tierney’s article in the New York Times devoted more space to repeating the tired arguments of carbon regulation naysayers than explaining what the scientists actually found. This spin totally misses the point.

It makes a lot of sense to promote policies that reduce local health threats and global warming simultaneously, such as cleaning up dirty diesels and plugging methane leaks. Replacing coal-fired power plants with energy efficiency and renewable energy also produces multiple benefits, but the naysayers quoted by Tierney don’t mention this obvious measure. And is it really easier to replace traditional cook stoves with cleaner burning models in millions of villages around the world than it is to pursue smart growth development strategies that reduce oil consumption, carbon emissions, and obesity? I’m not sure. But I do know that we need to be working on all of these strategies simultaneously to save lives and keep extreme weather in check.

Shindell and his international team have significantly advanced our understanding of the benefits of cutting smog, soot, and carbon dioxide at the same time. Let’s not get distracted by a silly debate about which to do first.