Optimal Path for Avoiding Dangerous Change and Short-lived Greenhouse Gases

By November 26, 2013 December 13th, 2013 Abrupt changes, Methane, Uncategorized

Methane (and natural gas), and black carbon (soot) are short-lived greenhouse gases relative to carbon dioxide, N20 (nitrous oxide) and CFC (chlorofluorocarbons). Limiting these short-lived greenhouse gases have obvious benefits in reducing warming. Focusing emissions reductions on these gasses also gives the benefit of delaying warming in the short-term, but really only in a world where we rather quickly limit emissions of long-lived greenhouse gases too.

Short-term limits on warming are very important because of climate tipping points. Abrupt climate change is common on our world. Twenty-three times in the last 100,000 years our climate has changed 9 to 14 degrees F globally and 18 to 27 across the Arctic. Sometimes it took millennia, often a century or less and when climate was being pushed the hardest (naturally), as little as a few years. (Alley) We are pushing our climate far harder than anything natural today.

In the long-term we are much more likely to develop solutions to treat long-lived climate pollution (CO2), but for the last 20 years our efforts have gone in reverse.  So much so that in the last 25 years we have emitted about as much CO2 as our civilization emitted in the previous 236 years.

If we actually begin to reduce CO2 within the next 35 years, immediate reduction of methane and black carbon (say from agriculture and emissions of smoke and forest burning) can result in a reductions of global temperature by 0.6 degrees C.

This study looked at a 25 and 78 percent reduction of methane and black carbon over a twenty year time span in several different long-lived greenhouse gas emissions reductions scenarios. Beginning emissions reductions of CO2 immediately a 0.6 degree C reduction in warming occurs, this is almost 30 percent. Delaying significant reduction of CO2 until 2050 means only and 18 percent reduction in total warming. But if we  persist in allowing our greenhouse gases to continue rising, we will see no more than a 10 or 15 year delay in the inevitable.

Even in the worst-case scenario studied here, there is a small delay in warming. This could be critical relative to the great risk of abrupt climate change. But we are likely to begin emissions reductions in earnest before then, in which case additional emissions reductions for methane and black carbon are greatly beneficial. They delay warming to begin with—which could be huge—and those emissions reductions would reduce overall warming in the long-term as well.

 

Bowerman et al., The role of short-lived climate pollutants in meeting temperature goals, Nature Climate Change, November 13, 2013.
http://www.nature.com/nclimate/journal/v3/n12/full/nclimate2034.html

 

Alley, Wally Was Right – Predictive ability of the North Atlantic Conveyor Belt Hypothesis for Abrupt Climate Change, Annual  Review of Earth and Planetary Science, February 2007.
http://shadow.eas.gatech.edu/~kcobb/abrupt/alley07.pdf