International negotiations to reduce carbon dioxide emissions and slow global warming are stuck in a stalemate. Many people in the United States – the world’s biggest economy and one of the planet’s top per capita greenhouse gas emitters – continue to doubt the reality of manmade climate change. After a brief dip during the financial crisis, CO2 emissions are on the rise again. Many climate scientists and policy-makers fear that the world’s nations will not act in time to avoid disastrous changes wrought by global warming.
Illustration by Michelle Kondrich, www.michellekondrich.com
So it was a rare bit of good news when, in February, low-lying, flood-prone Bangladesh, energy powerhouse Canada, eco-conscious Sweden, and climate-change-denier haven the US announced they were joining forces to curtail pollutants that are both exacerbating climate change and adversely affecting human health. Eager to find a strategy to slow global warming, these governments (joined in April by the European Union, Colombia, Japan, Nigeria, and Norway) have initiated a climate change mitigation program that focuses on a less-well known, but still dangerous, group of pollutants: black carbon (also called black soot), methane, and hydrofluorocarbons.
Together, these pollutants account for about one-third of global warming. Because they are short-lived – black carbon remains in the atmosphere for only days or weeks after it’s emitted, whereas carbon dioxide stays in the atmosphere for decades to centuries – curtailing these emissions would have an almost immediate effect. The technological fixes for reducing these pollutants are well tested and, equally important, available and relatively cheap. Experts say that slashing short-term pollutants may prove much easier to accomplish than the large-scale shift away from fossil fuels required for significant CO2 reduction. Success in limiting short-lived pollutants would deliver a much needed psychological boost to the movement to slow global warming and re-energize broader efforts to cut greenhouse gas emissions.
While by no means a panacea for addressing global warming or a substitute for CO2 reduction, the scientific consensus is that reducing black carbon and other short-lived climate pollutants is vital to combating climate change.
“This project holds a lot of promise, especially in the context of our larger battle against climate change,” Secretary of State Hillary Rodham Clinton said when she announced the coalition. “Now we know, of course, that this effort is not the answer to the climate crisis. There is no way to effectively address climate change without reducing carbon dioxide, the most dangerous, prevalent, and persistent greenhouse gas. It stays in the atmosphere for hundreds of years. So this coalition is intended to complement – not supplant – the other actions we are, and must be, taking.”
To be effective, the coalition needs to get moving immediately. Climate science shows that there’s a narrow window in which to act. Scientists estimate that by tackling short-term greenhouse gas pollutants, the currently projected global temperature rise could be reduced by nearly 0.5°C (or 2°F) by 2050. This might not sound like much, but it represents about one-fourth of the temperature rise climate scientists say must be averted to prevent long-term irreversible climate change. And given the international failure to address CO2 emissions, it’s likely the best way to avoid some of the most dire climate dislocations.
Black carbon is formed when fossil fuels, biofuels, or biomass – wood, vegetation or dung, for example – is burned but not fully combusted. Its sources include diesel engines – in motor vehicles, boats, trains, and also non-vehicle engines – as well as generators, agricultural burning, wildfires, inefficient cookstoves, and the kind of brick kilns that are common in South Asia. It is also emitted when excess gas from oil rigs and refinery wellheads is burned, or “flared.” This type of industrial pollution has created chronic environmental and health problems in regions where refineries are clustered, such as along the US Gulf Coast and Africa’s Niger Delta. Picture the heavy black smoke released when a diesel engine starts up, the black plume at the end of flaring industrial smokestack, or the curls that come off of wood smoke.
Black carbon, simply because it is black, absorbs more light than any other kind of particulate matter. When it settles on ice and snow it absorbs sunlight and makes them melt faster. In Arctic regions, these effects contribute to accelerated snow- and ice-melt and result in greater extents of open polar water that, in turn, allow for increased heat exchange that raises surface and air temperatures. The world’s Arctic glaciers are particularly vulnerable to the impacts of black carbon, as are glaciers in high-altitude regions such as the Himalayas. It’s estimated that black carbon emissions contribute about half the current warming effects in glaciated regions. This warming speeds spring snowmelt and thus affects when and how much water is available throughout the year for drinking, agriculture, and for natural vegetation. Because glaciers play such a pivotal role in global and regional climate patterns, slowing their melting will help mitigate climate change impacts over the short- and long-term.
“Aggressively reducing black carbon over the next 30 years could reduce currently projected warming in the Arctic by two-thirds,” says Erika Rosenthal, staff attorney with the environmental nonprofit Earthjustice and contributing author to the United Nations Environment Programme’s black carbon assessment.
Black carbon’s presence in the atmosphere can also affect cloud formation and lead to disrupted patterns of precipitation. While not directly linked to temperature change, such altered precipitation can have significant impacts on overall climate patterns. Scientists have already begun to link such disruptions – severe storms, droughts, and heat waves and their health effects – to climate change.
Black carbon also contributes to air pollution that has well-known impacts on respiratory and cardiovascular health. Black carbon is a component of the fine particulate pollution known as PM 2.5 (particulate matter of 2.5 microns or smaller). Exposure to particulate pollution contributes to some 2 million premature deaths worldwide each year. Another short-lived climate pollutant, methane, is a precursor to tropospheric ozone that also contributes to poor air quality. (The troposphere is the lowest region of the atmosphere extending from the earth’s surface upwards for 6 to 10 kilometers.) The public heath benefits of reducing these emissions will be substantial in virtually every region of the world, from heavily urbanized and industrial areas to remote and rural communities.
The good news is that measures to curtail short-lived climate pollutants, particularly black carbon, are readily available, relatively affordable, and don’t entail major changes in technology or energy-use habits. Diesel engine retrofits, new engine and fuel emissions requirements, alternate-transportation solutions, and clean-burning cookstoves are some of the proven technologies that could reduce short-term pollutants. For reasons coincidental to climate change mitigation, Rosenthal notes, “efficiency, cost savings, public health benefits” are concurrent goals.
Durwood Zaelke, president of the Washington, DC-based non-profit Institute for Governance and Sustainable Development, believes the new international initiative to curtail these pollutants has enormous potential. Because the results are, at least in theory, so readily achievable, the effort has the potential to “change the psychology” of the climate change movement and to take it “from denial to despair to optimism,” he said after the coalition’s first meeting in Stockholm. “That these governments have taken this step and so publicly is a major milestone,” Rosenthal adds.
Yet there are considerable challenges involved. UNEP experts point out that because the sources of black carbon tend to be so widely distributed and numerous – lots and lots of relatively small-scale sources like individual diesel engines, cookstoves, brick kilns, as well as large-scale sources like agriculture – implementing reductions will require concerted efforts. Luckily, the coalition will not have to start from scratch. It can build on ongoing international clean air and global warming control efforts such as the Montreal Protocol, Global Methane Initiative, Arctic Council, and Global Alliance for Clean Cookstoves. Financial commitments, including a UNEP-managed trust fund and $12 billion in support from the World Bank, are already in place.
Another challenge is quantifying results. That’s because emissions sources are varied and each pollutant gets measured differently. The best way to assess progress in reducing black carbon is by looking at specific emission sources, explains Earthjustice attorney Rosenthal. For example, one can count how many diesel vehicles have been retrofitted or how many clean-burning cookstoves have replaced inefficient ones, and estimate reductions that way.
It helps to have a picture of the global landscape of such emissions. While biomass burning – including wildfires – contributes about one-third of all black carbon emissions worldwide, contributions from other sources differ in ways that reflect regional variations in economic development. According to the US Environmental Protection Agency’s Report to Congress on Black Carbon, released in March 2012, black carbon emissions have been decreasing in North America and Europe over the past century but increasing elsewhere, particularly in developing economies in Asia and Latin America. The US now produces only about 8 percent of the world’s black carbon emissions; developing countries, about 75 percent.
The most striking difference in emissions sources is that of residential cookstoves. Globally, about one-quarter of black carbon emissions come from residential sources. Only a small fraction of North Americans depend on biomass-burning stoves. But about 3 billion people worldwide cook and heat their homes with stoves that burn wood, dung, other biomass, or coal. This raises the obvious issue of whether targeting cookstoves for emissions reductions means burdening the less wealthy and pushing the responsibility from those responsible for high per-capita emissions – American SUV drivers, for example – to those already at the low end of the income scale.
But the recognition of how critical these measures are to slowing global warming – combined with the important health benefits they can have – has won over those who were initially skeptical. Key to this, Rosenthal explains, was the decision to separate black carbon reduction efforts from the geopolitics of CO2 reduction and international agreements like the Kyoto Protocol. “Coalition members are very sensitive to these questions,” Zaelke says. “They will not advance an agenda that asks their people to do something they cannot do.”
Urgency is also a compelling factor. To be effective, short-lived climate pollutants need to be reduced before the world reaches what scientists call “peak warming” – the threshold beyond which climate conditions could become severely detrimental. A January 2012 paper by Drew Shindell – climate scientist at the Goddard NASA Institute for Space Studies – and colleagues, published in Science, makes this abundantly clear. To illustrate the impact of these reductions, the paper identifies and maps the effects of 14 different measures that would reduce about 90 percent of current black carbon and methane emissions. These include eliminating high-emission diesel engine vehicles, banning agricultural waste-burning, and replacing inefficient stoves, brick kilns, and coke ovens with clean-burning models.
A number of such programs are already underway. Efficient cookstove technology is being supported by the Global Alliance for Clean Cookstoves with funding from the US Department of Energy. In the US, new engine standards, particulate filters, “ultra-low” sulfur diesel fuel, and engine retrofit programs are expected to reduce diesel black carbon emissions by 86 percent by 2030.
But Shindell and colleagues are careful to note that while the public health and environmental benefits of reducing these short-term climate pollutants can be significant, over the long-term global warming mitigation will depend primarily on reducing CO2 emissions.
“We need to do more on the CO2 side,” Zaelke says. “But it’s hard to do more when you don’t have options. Acting on black carbon and other short-lived climate pollutants will help buy some time. This is something we can do now while we have options.”
“Given the already disrupted state of the climate, there’s not an either-or here,” says Bill McKibben, author and co-founder of 350.org, the international climate campaign. “We’ve got to do it all. If this is a substitute for reducing carbon, that will be sad. If it’s a supplement, it will be a real help.”
Elizabeth Grossman is the author of Chasing Molecules, High Tech Trash, and other books. Her work has appeared in Scientific American, Salon, The Washington Post, The Nation, Yale e360, and other publications.
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