For CO2, those reducing emissions pay the costs while the whole planet shares the benefits; the familiar recipe for a "tragedy of the commons".

While the situation is similar for methane, it is starkly different for BC and CO. Reduced emissions of those compounds will provide the largest benefits locally. This is especially true of air quality. Local crop yields increase and premature deaths due to air pollution decrease for areas reducing short-lived emissions.

Additionally, most methane, BC and CO emissions come from relatively small-scale activities. These are unlikely to generate the same fierce opposition that the fossil fuel industry has put up to reducing CO2 emissions, at least in the US, where it has effectively used weak campaign finance laws to encourage Congress to do what's best for the industry rather than what's best for society.

Though barriers to action are lower than for CO2, reducing emissions of short-lived warmers still requires concerted effort. Methane financing could help small stakeholders implement emissions reduction technologies. These sometimes pay for themselves, as the captured methane can be sold, but up-front costs can be prohibitive.

Local efforts to reduce BC and CO could be greatly boosted by increased international cooperation, technology transfer, and acknowledgement 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 serving the global community.

A forthcoming UN Environment Program assessment of BC and ozone will quantify the climate and air quality benefits of achievable BC, CO and methane emissions reductions, but it is already clear that aggressive action would save millions of lives and increase crop yields by millions of tons annually (worth billions of dollars) in addition to substantially reducing near-term warming. A push towards reducing these emissions now could also help build confidence among the negotiating partners.

We are not yet on a path to avoiding the worst effects of climate change. Additional actions are clearly needed. Reducing emissions of methane, BC and CO are not enough and cannot substitute or "buy time" for CO2 reductions, which need to begin quickly due to CO2's long lifetime. However, together with CO2 reductions, controls on short-lived pollutants could greatly improve our chances of keeping global warming to manageable levels while simultaneously saving millions of lives and helping feed the world's growing population.

The author is a senior scientist at NASA's Goddard Institute for Space Studies and Chair of the forthcoming United Nations Environment Program BC and ozone assessment.