“If there is a tipping point 20 years in the future of our current trajectory, then we are going to reach it, and whether there is more or less methane in the atmosphere at that time won’t make a difference…On the other hand, if we can stabilize atmospheric concentrations of greenhouse gases below 450 ppm (CO2 equivalents on the standard 100-year timeframe measure) by 2050, and then gradually reduce them, there is a good chance of avoiding a rise of more than 2 degrees by, say 2100.”

-J. Quiggan “Timescales and timeframes” (Mar 7, 2012)

FACT: Both Shindell et al. 2012 and a report from the United Nations in 2011 argued strongly that emissions of methane and black carbon (i.e. soot) must be controlled immediately.  Without such controls, regardless of whether or not carbon dioxide is controlled, the Earth will warm to 1.5 to 2 degrees C above the long-term average background by 2030 to 2045.

At these temperatures, a major change in the planet’s climate system become increasingly likely, and there is a high risk of positive feedbacks making it extremely difficult to control global warming.

PSE_UNEPWMOFig3Fig. Observed global mean temperature from 1900 to 2009 and projected future temperature under various scenarios of controlling methane + black carbon (BC) and carbon dioxide, alone and in combination. An increase to 1.5o to 2.0 o C above the 1890-1910 baseline (illustrated by the yellow bar) poses high risk of passing a tipping point and moving the Earth into an alternate state for the climate system. Source: UNEP/WMO 2011.

See also Howarth et al. 2012 background paper for the National Climate Assessment and Hanson et al 2007.

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