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  • Emissions cuts also offer quick health and crop benefits

Reducing methane and black carbon emissions could quickly tackle climate change while improving food security and people's health, especially in developing countries, a study reports.

Scientists identified 14 emission control measures that, when applied together, could reduce global warming by around 0.5 degrees Celsius by 2050, avoid up to 4.7 million premature deaths, and boost crop yields by up to 135 million metric tonnes by 2030.

Both black carbon (a component of soot) and methane in the atmosphere warm the climate, and black carbon is dangerous to health when inhaled. Methane is also responsible for boosting the production of ozone a gas that is useful for life on Earth when high up in the atmosphere where it screens some of the sun's radiation, but is dangerous lower down in the atmosphere where it damages plants, reducing agricultural productivity, and human health.

The range of technological and regulatory measures, reported today (13 January) in Science, include targeting methane emissions from livestock and rice farming, and black carbon emissions from cooking stoves. The estimated benefits of cutting these emissions would far outstrip the costs of doing so, the authors said.

South Asia and central Africa would reap the most health benefits and the Middle East would see the best yield improvements. This is because black carbon does not disperse evenly throughout the atmosphere and so cutting its emissions also has different regional effects.

Cutting black carbon emissions could reduce drought risk, for example in the Sahel, because of its effect on rainfall patterns, and reverse changing monsoon patterns in South Asia. China and India combined could grow 20 million extra tonnes of crops as a result. Brazil, Pakistan and the United States would also see great gains. Overall, gains could be worth around US$8 billion per year globally, the scientists claim.

Because black carbon, methane and ozone have short lifetimes, cutting them brings a quicker climate and health response than cutting CO2 emissions.

These quick local effects offer a win-win solution, said Martin Williams, professor of air quality research at the UK's Kings College London and an author of the study.

As most of the health and agricultural benefits are regional, it gives a real incentive to countries, particularly in the developing world, to reduce their emissions to combat climate change, he told SciDev.Net.

Paul Johnston, a senior research scientist for Greenpeace, welcomed the potential benefits but said the solutions offered for limiting climate change were a bit wide of the mark.

These measures can only delay global warming rather than prevent it, he said.

Ultimately, we are only going to have success if we remain focussed on carbon dioxide, Johnston said.

He added that the energy industry is the largest methane, black carbon and also carbon dioxide emitter. So dealing with far bigger CO2 emissions here would automatically generate some of the same benefits.

Williams acknowledged the concern, and said: Clearly, relying on short-term reductions [from ozone gases and black carbon] is not a complete solution. We need to combine this approach with long-term carbon reduction schemes if we are to keep below the two degree threshold.

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