Disentangling the effects of CO2 and short-lived climate forcer mitigation

Rogelj, J; Schaeffer, M; Meinshausen, M;  Shindell, DT; Hare, W; Klimont, Z; Velders, GJM; Amann, M; Schellnhuber, HJ

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Volume: 111, Issue: 46, Pages: 16325-16330, DOI: 10.1073/pnas.1415631111, Published: NOV 18 2014

Abstract: Anthropogenic global warming is driven by emissions of a wide variety of radiative forcers ranging from very short-lived climate forcers (SLCFs), like black carbon, to very long-lived, like CO2. These species are often released from common sources and are therefore intricately linked. However, for reasons of simplification, this CO2-SLCF linkage was often disregarded in long-term projections of earlier studies. Here we explicitly account for CO2-SLCF linkages and show that the short-and long-term climate effects of many SLCF measures consistently become smaller in scenarios that keep warming to below 2 degrees C relative to preindustrial levels. Although long-term mitigation of methane and hydrofluorocarbons are integral parts of 2 degrees C scenarios, early action on these species mainly influences near-term temperatures and brings small benefits for limiting maximum warming relative to comparable reductions taking place later. Furthermore, we find that maximum 21st-century warming in 2 degrees C-consistent scenarios is largely unaffected by additional black-carbon-related measures because key emission sources are already phased-out through CO2 mitigation. Our study demonstrates the importance of coherently considering CO2-SLCF coevolutions. Failing to do so leads to strongly and consistently overestimating the effect of SLCF measures in climate stabilization scenarios. Our results reinforce that SLCF measures are to be considered complementary rather than a substitute for early and stringent CO2 mitigation. Near-term SLCF measures do not allow for more time for CO2 mitigation. We disentangle and resolve the distinct benefits across different species and therewith facilitate an integrated strategy for mitigating both short and long-term climate change.

Link to full article: http://www.pnas.org/content/111/46/16325.abstract