Reducing short-lived pollutants
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Rapid growth in carbon dioxide (CO2) emissions must stop 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, the long time it stays in the atmosphere, creates seemingly insurmountable barriers to international agreements.
First, benefits from limiting CO2 emissions mostly occur only after many decades, which is well beyond the focus of most politicians or corporations. Second, nations disagree over whose emissions are most important.
However, CO2 is not the only driver of climate change. Other pollutants with shorter life spans also contribute. Black carbon (BC) is emitted during incomplete burning in sources such as brick kilns, coke ovens, diesel engines, biomass cookstoves and outdoor fires. These sooty particles absorb sunlight, warming the Earth.
Ozone in the lower atmosphere is a potent greenhouse gas, but 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 compared with ozone or BC, which last for only days to weeks in the atmosphere, methane's lifetime of about a decade means it is still short-lived relative to CO2.
Together, it is estimated that 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 warming and regional climate shifts. So these lesser-known pollutants are not just a small part of the problem. Furthermore, ozone and BC also degrade air quality.
These properties could lead to reduced barriers to international cooperation on emissions mitigation compared with CO2. Since they are short-lived, benefits would be felt very rapidly if emissions were reduced.
Governments and corporate boards may find it easier to take actions when the dividends will be enjoyed 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 influence are largely irrelevant.
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