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June 2012, No. 1 & 2 Vol. XLIX, The Future We Want?

Societies must find a way to stop the rapid growth in carbon dioxide (CO₂) emissions to avoid a disastrous future for our planet. As the greatest contributor to global warming, CO₂ is the natural focus of current climate negotiations. Unfortunately, one of the very properties that makes CO₂ so problematic¡ªthe long time it stays in the atmosphere¡ªcreates high barriers to efforts aimed at reducing its emissions. First, the benefits of limiting CO₂ emissions present themselves only after many decades, which is well beyond the focus of most politicians or corporations. Second, nations disagree over how much responsibility for reductions should be based on historical emissions or on current levels.

However, CO₂ and other long-lived greenhouse gases are not the only drivers of climate change. Pollutants with shorter lifespans also contribute. Black carbon (BC) is emitted during incomplete burning in sources such as brick kilns, coke ovens, diesel engines, stoves burning biomass for cooking and heating, and outdoor fires. These sooty particles absorb sunlight and warm the Earth. Another short-lived cause of warming is ozone in the lower atmosphere. Ozone is a potent greenhouse gas, but it is not emitted directly. It is produced by chemical reactions usually involving carbon monoxide (CO) or methane.

Thus, emissions of these precursors contribute to warming. The same sources that generate BC produce carbon monoxide. Methane is emitted by sources including coal mines, gas flaring, venting and transport, landfills, rice agriculture, and manure. Methane is a powerful greenhouse gas, in addition to leading to ozone formation. Though long-lived in comparison with ozone or BC, which last for only days to weeks in the atmosphere, methane's lifetime of about a decade means that, relative to CO₂, it is still short-lived.

Together, emissions of methane, CO and BC have contributed approximately the same amount to global warming as CO₂. Though uncertainties for BC are larger than for the others, it likely contributes substantially to both global warming and to larger regional climate shifts. So these lesser known pollutants are not merely a small part of the climate problem. Furthermore, ozone and BC also degrade air quality; ozone is toxic to both humans and plants, and BC particles are particularly damaging to humans as, being typically quite small, they can be inhaled deeply into the lungs where they lead to cardiovascular disease and lung cancer. Hence reductions in emissions of BC and ozone precursors will improve human health and food security, in addition to mitigating climate change.

Thus, while air quality and climate change have traditionally been regarded as separate problems with independent solutions, these two environmental issues overlap strongly where methane, BC and CO is concerned. Our recent research has identified emissions control measures for these pollutants that lead to substantial benefits in both reducing the rate of near-term climate change, and improving air quality. The measures consist of reducing methane emissions from coal mining, oil and gas production, long distance gas transmission, municipal waste and landfills, wastewater, livestock manure, rice paddies, and of reducing emissions from incomplete combustion in diesel vehicles, biomass stoves, brick kilns, coke ovens, and agricultural waste burning.

These measures, all using existing, proven technology, will reduce projected global warming by nearly half over the next three decades, while leading to between 1 and 4 million fewer premature deaths per year from outdoor air pollution, and to increased crop yields by 30 to 135 million tonnes per year. They would prevent many additional premature deaths from indoor pollution exposure, roughly 400,000 per year in India and China alone. They would also provide strong regional climate benefits by reducing disruption of traditional rainfall patterns, such as the South Asian monsoon or Sahel rainfall, with the greatest benefits found in the avoidance of regional climate change and regional deaths occurring in developing countries where emission controls are put in place.

The emissions control measures are also cost effective. For example, many of the methane emissions control measures pay for themselves as the captured methane can be sold (methane is the primary component of natural gas). Capturing gas during oil or gas extraction and separating and treating biodegradable waste from municipalities, instead of sending it to landfills, are particularly attractive measures in that respect. Looking at cost per tonne, most of the methane measures cost less $250, with many below $100 much less than the estimated health, climate, and agricultural benefits of $700 to $5,000.

Similarly, many of the BC emissions control measures are economically favourable. The control measures on brick kilns, coke ovens and stoves reduce emissions primarily by burning fuel more efficiently. Therefore, small industry recoups the cost of the more efficient kilns or ovens as they pay less for fuel. Similarly, more efficient stoves require less fuel, leading to reduced time spent gathering biomass, thereby leaving time for activities such as education for women, as well as reduced deforestation.

These health, agriculture, and development benefits make these measures substantially more appealing when taking a more holistic view than would be apparent from focusing solely on their climate impact (e.g., as in a Kyoto-type mechanism that compares CO₂ and methane based solely on their long-term climate impact).

Although barriers to action are lower than for CO₂, reducing emissions of short-lived warmers still requires a concerted effort. Methane financing could help small stakeholders implement emissions reduction technologies. As noted, these sometimes pay for themselves, but upfront costs can be prohibitive. Local efforts to reduce BC and CO could be greatly boosted by increased international cooperation, technology transfer, and awareness of the climate benefits produced. Such efforts are in each nation's own interest, as they would produce large air quality benefits, as well as serve the global community via reduced global warming. Encouragingly, efforts to boost emission controls of these pollutants have already begun with the announcement on 16 February 2012 of the Climate and Clean-Air Coalition to Reduce Short-Lived Climate Pollutants. This group, which consists of three developed countries (Canada, Sweden, and United States) and three developing countries (Bangladesh, Ghana, and Mexico) along with the United Nations Environment Programme, aims to foster widespread implementation of the measures described in our studies.

Some may worry that taking a broader view, which elevates the importance of those emissions that are damaging to both air quality and the climate, may distract from the real problem of dealing with CO₂ emissions in order to avoid long-term climate change. I believe that societies can and, in fact, must handle multiple problems simultaneously. Science argues for separating long-term climate change, governed primarily by CO₂ emissions, from near-term climate and air quality, governed by particulate and ozone precursor emissions, because both the emission sources and the impacts are generally distinct. There are good reasons to address both of these issues rather than only one or the other.

Picture someone going to the hospital with a broken leg, and the doctors discovering they also have treatable cancer. Would anyone argue that the broken leg should be ignored and all treatment be focused on the cancer since it's the more deadly problem over the long term? Of course not. It should be no different for climate change, and a balance between emissions control measures targeting CO₂, with a long-term benefit for future generations, and those targeting methane and BC, with rapid benefits over the next decades, is sensible.

Moreover, targeting only CO₂ could potentially lead to what we've seen in the past: failure to sufficiently reduce emissions. Our new research does not change the conclusion that CO₂ reductions are vital, but we've known that for decades now and yet remain in gridlock on lowering global growth. If we keep worrying only about CO₂ and its emissions continue to climb, we might get the worst of both worlds -- minimal CO₂ controls and minimal methane/soot controls. In addition, there are the millions who will die along the way from air pollution without enhanced methane/soot controls, and those who will suffer from greater climate disruption during the next few decades if we don't put these controls into place. While climate change in 100 years may have more dramatic effects, climate change in the next few decades has consequences, too, and for poor farmers struggling now or low-lying islands, the near-term may be all they have. More optimistically, the multiple benefits of reducing BC and methane could lead to increased international cooperation on emissions mitigation compared with CO₂. Governments and corporate boards may find it easier to take action when one of the dividends will be cleaner air on their watch. Furthermore, the effect on the climate of short-lived pollutants is primarily a result of their current emissions. Thus disputes about historical responsibility versus present day share of emissions are largely irrelevant. Success in reducing short-lived pollutants might even help inspire confidence in our ability to cooperate in limiting climate change, thereby building confidence among countries trying to negotiate CO₂ reductions.

For CO₂, those reducing emissions pay the costs, while the whole planet shares the benefits¡ªthe familiar recipe for a tragedy of the commons. While the situation is similar for methane in terms of environmental benefits, it is different in that the economic value of the captured methane goes to the one reducing emissions. For BC and CO, the situation is starkly different for the air quality benefits and the reduced disruption of regional rainfall, which is greatest in the regions where emissions are reduced. For areas reducing short-lived emissions, local crop yields increase and premature deaths due to air pollution decrease most strongly.

We are not yet on a path to avoiding the worst effects of climate change, with CO₂ emissions reaching new highs year after year. Additional actions are clearly needed. Reducing emissions of methane, BC and CO is not enough and cannot substitute or buy time for CO₂ reductions, which needs to begin quickly due to its long lifetime. However, together with CO₂ reductions, controls on short-lived pollutants could greatly improve our chances of keeping global warming at manageable levels while simultaneously saving millions of lives and helping feed the world's growing population. By slowing near-term warming, they would also allow for substantially greater time for adaptation to climate change over the next several decades.

Further information including links to scientific papers, the UNEP/WMO Integrated Assessment of Black Carbon and Tropospheric Ozone, and interactive visualizations showing the impacts of the emissions controls measures are available at

The author thanks all his colleagues who contributed to the Science paper "Simultaneously Mitigating Near-Term Climate Change and Improving Human Health and Food Security" and the United Nations Environment Programme/World Meteorological Organization (UNEP/WMO) "Integrated Assessment of Black Carbon and Tropospheric Ozone" that provide the scientific underpinning for this article.