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译:Soot strategies

来源: 时间:2011-1-26 14:19:00 点击:

As the power of black carbon to accelerate ice-melt becomes clearer, climate-change policymakers are giving more time to this long overlooked pollutant. Jenny Johnson reports.

Global efforts to mitigate climate change are beginning to take aim at a once-obscure pollutant called “black carbon” in a shift that may bring policies to cool the planet to families preparing meals at home and farmers readying plots of land for planting.

A series of new scientific studies have confirmed the potent warming effects of black carbon on melting ice and snow in the Arctic and the Himalayas, spurring a new focus on attacking sources of those emissions. The latest research identifies open burning in agricultural fields in Eurasia as a key source of black carbon in the Arctic. Evidence also indicates emissions from the burning of coal, wood and other biomass for domestic cooking and heating throughout Asia are heavily impacting the Himalayas.

Black carbon is part of a chemical mix of particulate matter that has long been an air-pollution concern due to its impacts on human health. But the pollutant also acts to reduce the reflectivity of ice and snow, allowing heat absorption and hastening surface melt. Research indicates reductions could immediately help save ice and snow in the Arctic and the Himalayas, two areas of critical global importance that are proving particularly sensitive to climate change.

Melting of Arctic ice presents several dangers for the planet. The process could undermine the region’s ability to act as a cooling mechanism for Earth by reflecting incoming solar radiation back into space and disrupt global ocean circulation by decreasing the salinity of water. Greenland, meanwhile, holds enough frozen water to raise sea levels – if melted – by as much as seven metres. These scenarios are increasingly realistic, as catastrophic loss of ice in the Arctic has accelerated in recent years, well beyond the predictions of climate models.

The Arctic is warming at two to three times the rate of the rest of the planet, with its rising temperatures constituting a possible global “tipping point”, which could result in rapid global warming and a cascade of changes through the ecosystem. Black carbon may have contributed as much as 50% of the 1.9 degrees Celsius of warming seen in the region since 1890, according to a 2009 paper published in Nature Geoscience.

Research shows that black carbon is also heavily impacting the glaciers of the Himalayas, another region of global significance. The “third pole” or “Asian water tower” feeds some of the world’s biggest rivers, including the Ganges, Yangtze and Yellow River, which together supply drinking water and crop-irrigation for some 1.5 billion people across 10 countries. According to estimates published last year in the journal Atmospheric Chemistry and Physics, black-carbon emissions have caused nearly 10% of the ice-cover loss in the Himalayas from 1990 to 2000, of which about 36% is attributed to Indian coal and biofuel burning.

Previously seen as a distraction from capping and reducing carbon dioxide, the nexus of air pollution and global warming is finally coming to the forefront of the climate-policy debate as evidence grows that so-called short-lived climate forcers like black carbon have big effects.

The shift in focus also comes against a background of continuing failure to set credible global policy on carbon-dioxide emissions. Black carbon can be effectively reduced through targeted, regional programmes that can help limit warming in the near term, something that cannot be done with carbon dioxide due to its longer atmospheric lifetime. And black carbon’s large and direct human health impacts, plus the fact it is already targeted by rapidly urbanising countries, make it an attractive target.

What next?

The latest research shows that due to a seasonal shift in a climatic anomaly called the Arctic Front, smoke from the widespread open burning of grass and straw that takes place in Eurasia in the late winter and early spring efficiently travels north to the Arctic, where particles from it land on the ice and snow.

Scientists have identified open burning in northern Eurasia – Russia, Kazakhstan, Mongolia and north-west China – as the single biggest source of black carbon in the Arctic and say that, at certain times of the year, it may constitute an even bigger contribution to warming in the region than carbon dioxide.

Sarah Doherty of the University of Washington in the United States used field samples to trace the origins of the black carbon coating snow in the Arctic to biomass burning in Eurasia. At a St Petersburg conference in November, she cautioned that the cooling effects of other particles in the smoke are “highly uncertain” and may dampen the warming impact of black carbon in the region. However, Doherty said that decreasing biomass burning in Eurasia would likely have the biggest single impact on reducing Arctic warming in the near term.

Controlling open burning is a major challenge. Farmers in China and Russia are officially prohibited from disposing of waste, recharging the soil and ridding their fields of pests through burning, but such bans have proved ineffective.

“In order to reduce China’s springtime black carbon emissions, farmers need a viable alternative method of crop waste removal,” a May 2009 report from US-based non-profit the Clean Air Task Force stated. Researchers are testing ideas for alternatives, such as using straw as a source of bioenergy, which would result in lower emissions. Processing waste for fertiliser is another leading idea.

In Russia, fire policy is coming under the spotlight following the summer's wildfires that burned vast areas of forest amid record heat and drought, destroying 30 villages and killing dozens directly and indirectly from smoke, smog and carbon monoxide effects. While the summer blazes are unlikely to have affected the Arctic on the scale of the spring fires due to climate patterns, critics say the events demonstrated a general lack of capacity on the part of the government to control fires across its large territory. They argue that, without greater capacity, it will be impossible to control the fires in the spring.

Several researchers have reported that the Kremlin is currently reviewing its forest code, which was changed in 2007, doing away with a unified forest protection system and giving more power to the regions. Major changes to the forest code are a top priority for environmental groups in Russia today and there is international pressure on Russian officials to act in time for the next fire season.

Action to decrease the black carbon affecting the Himalayas is more advanced. Several international development programmes are focused on distributing more efficient cooking stoves that greatly reduce emissions. However, the scale of the problem and the expectation that black-carbon emissions will continue to increase alongside Asian industrial development, still hinder effective policy.

The China-based group Third Pole Environment is conducting research into the many unanswered questions about sources and effects of emissions and how the region will respond to global environmental changes and has stressed the need for further work in this area. It is clear that even beginning to address the climate impacts of activities like grass and straw burning in Eurasia will take time. There are many knowledge gaps that prevent robust policy solutions, such as basic data on the types of crops in Russia and its land cover. The willingness of the countries to act remains an open question.

At a supranational level, there is some progress. While black carbon is not among the greenhouse gases addressed under the United Nations Framework Convention on Climate Change, a separate UN convention is set to begin shaping reduction policies to mitigate climate change. In December, the Convention on Long-range Transboundary Air Pollution (under the UN Economic Commission for Europe) agreed to revise one of its protocols in 2011 to include black carbon, as well as other short-lived climate forcers, such as carbon monoxide and methane.

This step will make it the first international body to begin shaping policies that account for the air pollutant's climate effects. Europe, the United States and Russia are among signatories to the convention. China is not, but the work plan for the coming year specifies the creation of policies that could be applied outside the area currently covered by the convention.

A series of new studies on black-carbon sources, effects and mitigation options are set to be published in 2011 by the United Nations and several high-profile research institutions. As understanding of the issue improves, advocates are hoping united solutions and action will quickly follow.


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由于一直以来都未能对二氧化碳排放制定可行的全球性政策,而这一背景也促使治理的重心发生了转移。通过具有针对性的区域项目可以有效降低炭黑排放,从而能够在短期内限制温度的升高。而对于二氧化碳而言,由于其在大气中的留存时间较长,因此无法在短期内达到限制温度升高的目的。 此外,炭黑还会直接对人类的健康产生重大的影响,再加上一些快速城市化的国家实际上已经将其作为减排目标等因素都让炭黑成为一个非常具有吸引力的治理目标。






美国非营利组织—净化空气任务组织在其2009年5月发表的一份报告中曾这样写道: “为了降低中国春季的炭黑排放,农民们需要一种可行的替代方式来清除农作物秸秆。”研究人员正在对一些替代性理念进行测试。比如说,将秸秆作为生物能源的来源,从而可以产生较少的排放。而另外一个主导理念就是通过垃圾处理,将其变为肥料。









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