Thursday, January 12, 2017

Are Regional (not Global) Interventions Needed to Reduce Impacts and Mitigate Climate Change?

Two people on the shore of the Pacific Ocean
The Rationale for Accelerating Regionally Focused Climate Intervention Research (17 page pdf, Michael C. MacCracken, Earth's Future, Nov. 14, 2016)

Today we review a proposal to focus on particular regions where effort to reduce climate impacts would be more effective and likely have fewer unintended negative consequences than efforts aimed at the globe as a whole. Included in the potential approaches are modifying arctic warming by injecting sulfate aerosols directly into the Arctic atmosphere, moderate the intensity of tropical cyclones by brightening cloud albedoes, slowing the melting of Greenland and Antarctic ice sheets by blocking ice streams, and compensate for the reduced cooling from SO2 emissions in Asia by brightening the Pacific Ocean.

Key Quotes:

“Global-scale climate intervention is seen as a potential emergency backstop, even though the impacts from initiating melting of the polar ice sheets and biodiversity loss may well be irreversible and even undertaking testing steps in the intervention process outside the laboratory are controversial, at best”

 “model-based simulations ..… project global average temperature to increase to 3-4ºC above its preindustrial level by 2100 “

“surface-based approaches to altering energy flows as a means for moderating adverse regional impacts might well pose less difficult governance challenges and more regionally constrained evaluations of intended outcomes and unintended consequences. “ “near-term reductions in positive radiative forcing could most rapidly be achieved by reducing the atmospheric loadings of short-lived species (particularly methane, black carbon, and tropospheric ozone). “

 “The potential for moderating amplified Arctic warming:
  • high-latitude injection of sulfate aerosols into the stratosphere not only cooled the Arctic, but also, due to their roughly one-year half-life, spread to sub-Arctic latitudes and depressed the summer monsoon.
  • Potential approaches ....include brightening land, ocean, and clear and/or cloudy skies during the sunlit season .. reversing the warming influence caused by reducing air pollutant emissions flowing into the region … and, during the fall and winter seasons, cirrus thinning … bypassing the thermal barrier created by the sea ice ..and ice thickening by pumping sea water up onto existing sea ice.”
“The potential for moderating ocean warming in the tropical cyclone intensification zones:
* moderate the intensification effect of warmer ocean waters in only a few specific regions, so the amount of sea salt and/or sulfate aerosols needed to brighten clouds in only a few regions might well remain within reasonable bounds”

“The potential for slowing mass loss from the Greenland and Antarctic Ice Sheets:
*In addition to approaches involving physically blocking the exits of ice streams that may well be unworkable, approaches to consider might include cloud brightening, injection of reflective bubbles, and vertical mixing to lower the temperature of the waters that are observed to be inducing melting at the faces of ice streams. “

“The potential for a regional replacement for the loss of global sulfate cooling:
  • the centroid of the 0.5-1.0ºC cooling influence resulting from SO2 emissions has moved from the North Atlantic basin to southern and eastern Asia, a region where the per-ton-of-emission influence of SO2 emissions is likely larger due to the higher amounts of incoming solar radiation
  • inducing modest clear and cloudy sky brightening in the troposphere over the vast Pacific Ocean that would cause changes in the global energy balance comparable to those induced by the present highly concentrated, health-damaging sulfate loading presently centered over China, India, and downwind would seem to be possible as an alternative global-scale climate intervention”

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