A new study building on previous findings by scientists at Scripps Institution of Oceanography, UC San Diego, highlights 14 key air pollution control measures that if implemented could slow the pace of global warming, save millions of lives and boost agricultural production.
The research, led by Drew Shindell of NASA's Goddard Institute for Space Studies (GISS) in New York City, finds that focusing on these measures could slow global mean warming 0.5 degrees C (0.9 degrees F) by 2050, prevent between 0.7 and 4.7 million premature deaths each year and increase global crop yields by up to 135 million tons per season. While all regions of the world would benefit, countries in Asia and the Middle East would see the biggest health and agricultural gains from emissions reductions.
"We've shown that implementing specific practical emissions reductions chosen to maximize climate benefits would also have important 'win-win' benefits for human health and agriculture," said Shindell. The study is published in the Jan. 13 edition of journal Science.
Shindell and a large team of colleagues from around the world considered about 400 control measures based on existing, proven technology, but focused their analysis on 14 that would have the greatest climate benefit. All 14 would curb the release of either black carbon or methane, pollutants that harm human or plant health while simultaneously exacerbating climate change.
Veerabhadran Ramanathan, a climate and atmospheric scientist at Scripps and a report coauthor, said that implementing the measures could delay by several decades the onset of damaging climate change-related effects on natural systems and society. In May 2010, Ramanathan and coauthor Yangyang Xu identified three actions that could help keep global warming under 2 degrees C from pre-industrial temperatures. In a paper published in Proceedings of the National Academy of Sciences, the Scripps researchers said that reducing emissions of short-lived greenhouse agents like methane and fluorocarbons, stabilizing carbon dioxide levels in the atmosphere and creating "warming-neutral" strategies to curb emissions of aerosols and gases in air pollution that produce the greenhouse gas ozone. The last of these strategies would need to strike a balance between removal of aerosols such as sulfur that cool the atmosphere with removal of aerosols that warm the atmosphere such as soot and other types of black carbon, the authors said.
"By broadening our attention to the short-term climate warming agents, there is a real possibility for slowing down the rate of warming significantly in the coming decades," said Ramanathan. "What is striking is that it can be done with measures that are implementable using available technologies and existing institutions. For example, California has implemented some of the measures outlined in our study with demonstrable results."
Black carbon, a product of burning fossil fuels or biomass such as wood or dung, can worsen a number of respiratory and cardiovascular diseases. The small particles also absorb radiation from the sun causing the atmosphere to warm and rainfall patterns to shift. In addition, they darken bright land surfaces, such as ice and snow, reducing their reflectivity and hastening global warming.
Methane, a colorless and flammable substance that's a major constituent of natural gas, is both a potent greenhouse gas and an important precursor to ground-level ozone. Ozone, a key component of smog and also a greenhouse gas, damages both crops and human health.
Shindell and his team concluded that control measures would deliver Tajikistan, Kyrgyzstan and Russia - countries with large areas of snow or ice cover - the greatest protection against global warming, while the south Asian countries of Bangladesh, Nepal, and India would see the biggest reductions in premature deaths. Iran, Pakistan and Jordan would experience the most improvement in agricultural production. And southern Asia and the Sahel region of Africa would see the most beneficial changes to precipitation patterns.
Black carbon and methane have many sources and reducing emissions would require that societies make multiple infrastructure upgrades. For methane, the key strategies the scientists considered were capturing gas that would otherwise escape from coal mines and oil and natural gas facilities, reducing leakage from long-distance pipelines, preventing emissions from city landfills, updating wastewater treatment plants, aerating rice paddies more, and limiting emissions from manure on farms.
For black carbon, the strategies analyzed include installing filters in diesel vehicles, keeping high-emitting vehicles off the road, upgrading cook stoves and boilers to cleaner burning types, installing more efficient kilns for brick production, upgrading blast furnaces and banning agricultural burning.
The scientists used computer models developed at GISS and the Max Planck Institute for Meteorology in Hamburg, Germany, to model the impact of emissions reductions. The modeling showed widespread benefits from the methane reduction because methane is evenly distributed throughout the atmosphere.
In contrast, benefits from reducing black carbon, which falls out of the atmosphere after a few days, were stronger in certain regions than others. The effect of reducing black carbon, for example, would be particularly strong in areas with large amounts of snow and ice. In the Himalayas and the Arctic, such reductions would reduce projected warming over the next three decades by up to two-thirds.
"Protecting public health and food supplies may take precedence over avoiding climate change in most countries, but knowing that these measures also mitigate climate change may help motivate policies to put them into practice," Shindell said.
While carbon dioxide is the primary driver of global warming over the long-term, limiting black carbon and methane are complementary actions that would have a more immediate impact because these two pollutants circulate out of the atmosphere more quickly.
"The scientific case for fast action on these so-called 'short-lived climate forcers' has been steadily built over more than a decade, and this study provides further focused and compelling analysis of the likely benefits at the national and regional level," said United Nations Environment Program (UNEP) Executive Director Achim Steiner.
The new study builds on a UNEP/World Meteorological Organization report, also led by Shindell, published last year. It also builds on the UNEP- Atmospheric Brown Clouds project led by Ramanathan that was published in 2008.
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