Some scientists have proposed drastic cuts in the emissions of soot, methane, and other strong but short-lived greenhouse gases as a way to tackle global warming in the short term. But such approaches won’t lessen the long-term rate of climate change, a new study confirms.
At current emission rates, methane and soot (from industrial activity as well as from vehicles, image) spewed into the atmosphere between 2010 and 2020 will increase the eventual peak in global average temperature by only a few hundredths of a degree, the analysis suggests.
But emissions of carbon dioxide and other long-lived greenhouse gases during the same 10-year period will eventually boost peak warming about 10 times that amount, the researchers report online today in Nature Climate Change.
The difference, the researchers explain, is due to disparities in the atmospheric lifetimes of these planet-warmers: Although methane and soot exert much stronger greenhouse gas effects than carbon dioxide does, they persist in the atmosphere, on average, only 12 years and a few weeks, respectively; CO2, on the other hand, sticks around for centuries.
While trimming emissions of methane and soot can indeed delay warming in the short term, those measures—whether they’re taken almost immediately or implemented a couple of decades from now—will be largely irrelevant for the global climate if emissions of carbon dioxide continue unabated.
The report, Continued Global Warming After CO2 Emissions Stoppage, introduction explains:
'Recent studies have suggested that global mean surface temperature would remain approximately constant on multi-century timescales after CO2 emissions are stopped. Here we use Earth system model simulations of such a stoppage to demonstrate that in some models, surface temperature may actually increase on multi-century timescales after an initial century-long decrease. This occurs in spite of a decline in radiative forcing that exceeds the decline in ocean heat uptake—a circumstance that would otherwise be expected to lead to a decline in global temperature.
The reason is that the warming effect of decreasing ocean heat uptake together with feedback effects arising in response to the geographic structure of ocean heat uptake overcompensates the cooling effect of decreasing atmospheric CO2 on multi-century timescales. Our study also reveals that equilibrium climate sensitivity estimates based on a widely used method of regressing the Earth’s energy imbalance against surface temperature change are biased. Uncertainty in the magnitude of the feedback effects associated with the magnitude and geographic distribution of ocean heat uptake therefore contributes substantially to the uncertainty in allowable carbon emissions for a given multi-century warming target.'
The article can be downloaded from the Nature Climate Change website at a cost of £22
Source: ScienceMag / Nature Climate Change
