A new study building on research from scientists at the Scripps Institution of Oceanography shows key emissions reduction measures could slow the pace of climate change, save lives and increase agricultural production.
The research, led by Drew Shindell of NASA's Goddard Institute for Space Studies finds focusing on these measures could slow global mean warming 0.9 degrees Fahrenheit by 2050, prevent between 700,000 and 4.7 million premature deaths each year, and increase global crop yields by up to 135 million tons each season.
The research continues work previously published by U.C. San Diego Scripps Institution of Oceanography climate and atmospheric scientist Veerabhadran Ramanathan, who co-authored the latest report.
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.
Shindell said 14 practical control measures based on existing, proven technology, 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.
The study is published in the Jan. 13 edition of the journal Science.
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.
Ramanathan said implementing the strategies could slow - but not stop - the effects of climate change.
"So employing these practical measures we not only delay the onset of so-called 'dangerous warming' by 20 to 30 years at the minimum, we also save millions of lives and save millions of tons of crop damages by air pollution," Ramanthan said. "So this is really a win-win for everyone."
In May 2010, Ramanathan and another scientist co-author Yangyang Xu identified three actions that could help keep global warming under 2 degrees Celsius from pre-industrial temperatures.
In a paper published in Proceedings of the National Academy of Sciences, the Scripps researchers write about reducing emissions of shortlived 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, which cool the atmosphere, with removal of aerosols which 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 in people. 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.
Ramanthan said he hopes world leaders will pay attention to the research and take steps to implement the changes.
"They should not take their eye off the carbon dioxide emissions, they should work on it, but these measures will have immediate effects," said Ramanthan.
But he said many of the measures can be put into place on a local level by cities and counties.
"The technology is here and California has shown the way in some cases," Ramanthan said. "And this is not about science; we've shown how these measures work on a street level in local and regional municipalities."
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. 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.
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.
