Climate Threat from Short-Lived Climate Pollutants Upgraded by IPCC in 5th Assessment

Black carbon GWP included for first time, at double previous estimates

GWP for methane also increased by as much as 30%

Targeted SLCP mitigation strategies can deliver more climate benefits than previously thought

Washington, DC, 2 October 2013 — The climate threat posed by short-lived climate pollutants was just upgraded by the Intergovernmental Panel on Climate Change’s (IPCC) in its Fifth assessment published this week. When feedbacks are included, the global warming potential (GWP) of methane, the number two climate warming gas, was increased by as much as 30% over estimates from 2007 and 60% over 2001. And for the first time the IPCC includes a GWP for black carbon.

Confirming an earlier multi-year assessment this year, the IPCC estimates that over a 100-year timespan black carbon is 900 times more powerful than carbon dioxide at warming the atmosphere. While the previous IPCC assessment did not include numbers for the GWP of black carbon, calculations based on the data provided would have produced a GWP of 460 over a 100-year timespan, about half the new number. Because of its short lifetime in the atmosphere, black carbon is 3,200 time more powerful than carbon dioxide over a 20-year timespan.

The GWP for methane was increased, from 25 to 28 over a 100-year timespan and from 72 to 84 over a 20-year timespan. When carbon-climate feedbacks are taken into account, the 100-year GWP of methane increases to a punishing 34 times that of carbon dioxide. Methane is a growing source of emissions in many countries including the United States due to increased use of natural gas for energy.

Both methane and black carbon are part of a group of pollutants, along with tropospheric ozone and hydrofluorocarbons (HFCs), known as short-lived climate pollutants (SLCPs) because they clear out of the atmosphere in a matter of days to a decade and a half. Aggressively cutting SLCPs has the potential to avoid as much as 0.6°C of warming by mid-century and as much as 1.5°C by 2100.

“Even before the new IPCC assessment, we knew that cutting these climate pollutants could cut warming in half and by two-thirds in the vulnerable Arctic for many decades,” stated Durwood Zaelke, President of the Institute for Governance & Sustainable Development. “Now we know that this strategy is even more important than we first thought.”

Because three SLCPs are potent air pollutants, cutting them can save millions of lives every year, while significantly increasing crop yields, making such efforts important for promoting sustainable development. In South Asia, for example, air pollution is the leading preventable cause of disease, according to a recent report by the World Health Organization.

Zaelke added, “Rapid cuts in CO₂ emissions are necessary to stabilize long-term temperatures, but in the near-term, aggressively cuts in SLCPs can provide fast benefits for climate, health, and food security benefits, particularly in the critical vulnerable regions that are already suffering some of the worst impacts of climate change.”

The IPCC AR5 is here.

IGSD’s Primer on Short-Lived Climate Pollutants is here.