<div><font size="4">Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO<sub>2</sub> emissions</font> </div>
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<div><a href="http://www.pnas.org/content/106/49/20616.full">http://www.pnas.org/content/106/49/20616.full</a></div>
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<div>August 31, 2009 </div>
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<div>A few quotes from this very important and well researched article focusing on means to address anthropogenic climate change other than lowering CO2 emissions:</div>
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<div>"Current emissions of anthropogenic greenhouse gases (GHGs) have already committed the planet to an increase in average surface temperature by the end of the century that may be above the critical threshold for tipping elements of the climate system into abrupt change with potentially irreversible and unmanageable consequences. This would mean that the climate system is close to entering if not already within the zone of “dangerous anthropogenic interference” (DAI). Scientific and policy literature refers to the need for “early,” “urgent,” “rapid,” and “fast-action” mitigation to help avoid DAI and abrupt climate changes. We define “fast-action” to include regulatory measures that can begin within 2–3 years, be substantially implemented in 5–10 years, and produce a climate response within decades." </div>
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<div>"Fig. 1 <a href="http://www.pnas.org/content/106/49/20616/F1.large.jpg">http://www.pnas.org/content/106/49/20616/F1.large.jpg</a> presents their results for various policy-relevant tipping elements (<a id="xref-ref-9-3" class="xref-bibr" href="http://www.pnas.org/content/106/49/20616.full#ref-9">9</a>), most of which Lenton et al. (<a id="xref-ref-8-3" class="xref-bibr" href="http://www.pnas.org/content/106/49/20616.full#ref-8">8</a>) include in their analysis; for elimination of Arctic summer sea ice and melting of the Himalayan-Tibetan glaciers and the Greenland Ice Sheet, the probability that the committed warming exceeds the tipping point temperature is estimated to be larger than 50%, and it is estimated to be >10% for dieback of the Amazon Rainforest, more persistent and higher amplitude El Niño conditions, reorganization of the North Atlantic Thermohaline Circulation, and melting of the West Antarctic Ice Sheet." </div>
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<div>"Even when CO<sub>2</sub> emissions stop, climate change is largely irreversible for 1,000 years (<a id="xref-ref-15-1" class="xref-bibr" href="http://www.pnas.org/content/106/49/20616.full#ref-15">15</a>, <a id="xref-ref-16-1" class="xref-bibr" href="http://www.pnas.org/content/106/49/20616.full#ref-16">16</a>). Efforts to limit CO<sub>2</sub> emissions alone may not be sufficient to avoid or reduce the risk of DAI on a decadal time scale, including the risk of abrupt climate change from committed warming (<a id="xref-ref-8-5" class="xref-bibr" href="http://www.pnas.org/content/106/49/20616.full#ref-8">8</a>, <a id="xref-ref-9-8" class="xref-bibr" href="http://www.pnas.org/content/106/49/20616.full#ref-9">9</a>)." </div>
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<div>"We discuss four of the available fast-action regulatory strategies that can begin within 2–3 years and be substantially implemented within 5–10 years, with the goal of producing desired climate response within decades. The first is to phase down the production and consumption of HFCs with high global warming potential (GWP), accelerate the phase-out of hydrochlorofluorocarbons (HCFCs), and recover and destroy stratospheric ozone-depleting GHGs in discarded products and equipment. The second is to reduce emissions of BC, giving priority to emissions that affect regions of snow and ice, including the Arctic, Greenland, and the Himalayan-Tibetan glaciers. The third is to reduce pollutant gases that lead to formation of tropospheric (lower atmosphere) ozone, a significant GHG. The fourth is to expand biosequestration through improved forest protection and biochar production." </div>
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<div>Vision2020 Post: Ted Moffett</div>