Abby L. Harvey
GHG Monitor
11/7/2014
While the near-term benefits of reducing short-lived climate forcers (SLCFs) like methane and black carbon are not to be dismissed, they are not significant enough to justify the delay of immediate mitigation of carbon dioxide, according to a study published this week in the Proceedings of the National Academy of Sciences. The study, conducted by a group of researchers from Germany, Austria, the Netherlands, the United States, Australia and Switzerland, found that mitigating SLCFs cannot replace efforts to mitigate CO2, which stays in the atmosphere much longer. “Our study demonstrates the importance of coherently considering CO2–SLCF co-evolutions. 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,” the paper says.
A major issue in explaining the importance of addressing CO2 concentrations is that SLCFs are often emitted from the same sources, making it very difficult to differentiate between the effects of mitigating one and not the other, according to the study. “Human activities, like fossil-fuel burning, result in emissions of radiation-modifying substances that have a detectable, either warming or cooling, influence on our climate. Some, like soot (black carbon), are very short lived, whereas others, like carbon dioxide (CO2), are very persistent and remain in the atmosphere for centuries to millennia. Importantly, these substances are often emitted by common sources. As climate policy is looking at options to limit emissions of all these substances, understanding their linkages becomes extremely important,” the paper says
In order to mitigate climate change in a lasting manner, CO2 concentrations have to be addressed right now, the study finds. According to the paper, at current CO2 emissions rates, “each decade of delayed CO2 mitigation implies around 0.17 [degrees Celsius] further warming over multiple centuries,” and while mitigating SLFCs does have an effect, it is not sufficient, nor is it lasting. “In none of our cases can [black carbon] related measures compensate for the persistent impacts of unabated CO2 emissions. Without early and stringent CO2 mitigation, warming from 2050 onward will become increasingly larger than what SLCF measures can reduce,” the paper says, going on to warn that, “delaying stringent action on CO2 results in lock-in of carbon emitting infrastructure and higher cumulative CO2 emissions that imply a higher committed warming. Because of this, and the persistence of CO2 in the atmosphere, near-term initiation of CO2 mitigation is required to control midcentury to long-term climate change. Replacing near-term CO2 reductions with SLCF mitigation leads to a higher risk that stabilization of concentration and warming is not achieved.”
