Synthetic Controls

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Science  07 Mar 2014:
Vol. 343, Issue 6175, pp. 1059
DOI: 10.1126/science.343.6175.1059-b

Most of the anthropogenic warming of climate caused by greenhouse gas emissions is due to radiative forcing by carbon dioxide, the molecule that has garnered the lion's share of public attention. It is not the only emitted gaseous species that affect climate, however. Another class of compounds, long-lived synthetic greenhouse gases (SGHGs; gases with no significant natural sources and lifetimes of at least 1 year), has received far less attention although its constituents are responsible for a significant amount of warming, providing nearly 20% of the direct radiative forcing increase due to carbon dioxide since the preindustrial era. Rigby et al. examine recent trends in 25 of the most abundant SGHGs and construct emissions scenarios in order to estimate their future impacts on global warming. They find that if the relevant recommendations of the Montreal Protocol are implemented, overall SGHG radiative forcing would be reduced by approximately 26% by 2050, as compared to a policy without such controls, a cumulative reduction equivalent to 0.5 to 2.8 years of carbon dioxide emissions at current levels.

Geophys. Res. Lett. 10.1002/2013GL059099 (2014).

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