Groundbreaking New Study Shows How to Reduce Near-Term Global Warming

By Andrew Freedman

Let’s face it — the prospects for containing global climate change by slashing emissions of greenhouse gases, such as carbon dioxide, are looking rather bleak these days. International treaty talks are proceeding at a snail’s pace, and after dipping during the global recession, emissions of carbon dioxide (CO2) — the most important greenhouse gas — from the energy sector climbed to record levels this year, and studies show that the effects of climate change, such as sea level rise, are now expected to be much worse than previously thought.

Now what if I told you that we could slash the rate of global warming nearly in half during the next several decades, while saving as many as 4.7 million lives a year and boosting crop yields, by addressing non-CO2 global warming agents? And, that we wouldn’t need endless rounds of United Nations climate negotiations in order to do it? You’d probably think it sounds too good to be true, like some sort of late night global warming infomercial.

According to a group of 13 scientists from the U.S., Europe, Africa and Asia, these goals are actually well within reach, and could be accomplished by tackling emissions of short-lived global warming agents such as soot and methane, a precursor to low-level ozone formation and a greenhouse gas in its own right.

The baker’s dozen of scientists make their case in a study published today in the prominent journal Science. Led by NASA researcher Drew Shindell, the study builds upon a report published in November by the U.N. Environment Programme, which also found major benefits to reducing emissions of what are known in global warming lingo as “short-lived climate forcers.”

But the new work goes beyond any other studies by identifying practical ways to reduce short-lived global warming agents, modeling how the climate system may respond to these measures, and then estimating whether the benefits would exceed the costs of taking such steps. This comprehensive approach offers a clearer path forward for policy makers to implement these solutions.

Controlling emissions of CO2 (purple line) is the only way to limit global warming in the long-term. In the next two decades, however, limiting emissions of black carbon and methane (blue line) could have a significant impact. Limiting emissions of CO2, black carbon and methane (pink line) would have an even stronger short- and long-term impact. Credit: UNEP/Shindell

The short-lived global warming pollutants are distinct from CO2, which has hogged the limelight of global climate policy efforts for decades, since they remain in the atmosphere for a relatively short period. Whereas CO2 emitted today can remain in the atmosphere for centuries, the atmospheric lifetimes of pollutants such as soot (technically known as black carbon), as well as methane (a powerful greenhouse gas), are far shorter. Soot, for example, only stays in the air for several hours to a couple of weeks before precipitation rinses it out or chemical processes break it down.

So, as the study demonstrates, while cutting emissions of CO2 won’t have a tangible impact on global warming for another several decades, if we were to target the short-lived pollutants, we could counter some portion of global warming in the near-term. And, since methane contributes to low level ozone pollution that damage crops and human health, and soot also aggravates respiratory and cardiovascular illness, we could make dramatic gains in other areas as well.

The study is groundbreaking in that it’s the first time that scientists have quantified both the climate benefits of specific measures to reduce short-lived warming agents and performed a cost benefit analysis on these approaches.

Shindell and his colleagues found that the 14 emissions reduction actions they zeroed in on would be relatively cheap, and can be implemented with existing technologies.

“[By] applying existing, proven technology you can have large enough effects on emissions that you can really realize very substantial benefits for both climate and air quality, health and agriculture,” Shindell said in an interview with Climate Central.

Scientists have discovered soot deposits dating back to the 1950's in glacier ice cores. Most soot found in those regions comes from diesel engines, coal-fired power plants and outdoor cooking stoves. Credit: WikiMedia Commons.

To cut methane, the study looks at strategies such as capturing gas currently escaping from coal, oil and gas facilities and controlling emissions from landfills. To control soot, policies include installing filters on diesel vehicles to capture soot emissions, and increasing the use of clean-burning cookstoves in developing countries.

The study shows that reducing methane emissions would make the biggest contribution to slowing the rate of global warming by 2050, but that tackling black carbon emissions would also provide a range of benefits, particularly at the regional level.

Soot warms the air by absorbing radiation from the sun, and when it lands on snow and ice it darkens the surface, causing more melting. The study finds that cutting black carbon emissions would reduce warming in the Himalayas and the Arctic during the next 30 years by as much as two-thirds, and would even help maintain the current South Asian monsoon.

Studies have shown that pollution in South Asia, including soot, may be altering the timing and geographic extent of the monsoon seasons, which would have major consequences for agricultural production.

Black carbon also harms public health, especially in developing countries, where wood, dung and other fuels that emit soot when burned are used for cooking. Implementing soot-reduction policies would avoid 373,000 premature deaths each year in India and China alone, the study states.

As NASA’s Shindell is quick to caution, addressing short-lived global warming pollutants won’t render CO2 reductions unnecessary. “It would be a bad thing if this were a substitute for action on CO2,” Shindell said.

But, he added, “It would also be wrong to ignore these pollutants because they have this powerful leverage on climate over the next several decades that everyone on the planet now has to live through.”

Durwood Zaelke, president of the Institute of Governance and Sustainable Development, who is working to implement some of the policies detailed in the study, said short-lived pollutants may account for around half of the global warming to date, which means “You can’t solve climate change without doing both.”

Perhaps the biggest advantage to pursuing cuts in methane, black carbon and other short-lived pollutants is that they don’t require that an agreement be reached through the cumbersome United Nations climate negotiations. Instead, policies can be implemented at national, regional, and local levels, Zaelke said.

“[We’re] moving into a multi-venue climate policy where we’re going to need to enlist all of the laws and institutions that can do a piece of climate solutions,” he said. As Zaelke noted, moving forward with the steps detailed in this study and other recent reports would build confidence that we can, in fact, make progress in reducing climate change.

Perhaps even more importantly, cutting emissions of methane and black carbon, he said, would “give you the sense of building some momentum while we continue to wrestle CO2 to the mat.”

Given the seemingly endless stream of depressing climate change news, some confidence-building measures, such as the ones analyzed in the study, could be exactly what we need.

Online Resources:
Interactive maps and graphs of country-by-country emissions reductions
http://www.giss.nasa.gov/staff/dshindell/Sci2012/

NASA Image Gallery:
http://www.flickr.com/photos/nasa_goddard/sets/72157628811914645/