Beyond the pseudo "debate" about whether man-made climate change is underway is a much more serious debate about whether our carbon reduction targers are sufficiently stringent. In the Summary for Policymakers prepared by Working Group III for the IPCC Fifth Assessment Report released in April,it was reported with "high confidence" that despite international efforts to reduce greenhouse gasses (GHG), they have continued to increase from 1970 to 2010 with a faster rate of increase toward the end of that period. The annual rate of increase from 1970 to 2000 was 1.3%, but from 2000 to 2010 was 2.2%.
Also reported with "high confidence" was that CO2 emissions from fossil fuel combustion and industrial processes contributed about 78 % of the total GHG emission increase from 1970 to 2010. Finally, the report concluded that without additional efforts beyond those in place today, global mean surface temperature would rise by 2100 to a level from 3.7° C to 4.8° C, a level all agreed would be catastrophic.
To avert these consequences, the summary states with high confidence that keeping global mean surface temperature rise less than 2° C relative to pre-industrial levels will require keeping atmospheric CO2 concentrations under 450 ppm. Staying under that limit by 2100 would require a 40% to 70% reduction in GHG by 2050 over the level in 2010. The Summary states with high confidence that the Cancun Pledges for reductions in GHG by 2020 are inadequate.
If that Summary is not sufficiently dire, turn to 350.org, which bases its international campaign to reach 350 ppm at least in part on this quote from James Hansen, the former head of the Goddard Institute for Space Studies: "If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from [current levels] to at most 350 ppm."
In December 2013, Hansen published an article with 16 coauthors stating flatly that "a 2°C warming would have major deleterious consequences.... Global warming of 2°C would be well outside the Holocene range and far into the dangerous range." To return to 350 ppm by the end of this century, Hanson and his coauthors estimate we will need a 6% per year reduction in carbon emissions beginning in 2013, assuming substantial reforestaton to absorb carbon. Hansen estimates that delaying fossil fuel emission reductions until 2020, assuming 2%/year emissions growth in the meantime, would cause CO2 to remain above 350 ppm until 2300.
The policy implications of this debate are enormous. The IPCC meeting in Paris this Fall is not likely to take a more aggressive tack than the Working Group III Summary reported above. Hopefully as the science becomes clearer based on observation of current trends and less on models, the climate change deniers will lose influence and serious shifts to alternative sources of energy will receive the support they need.