A recent Newsweek article discussing Al Gore’s new book made reference to recently published work on how different gases are contributing to anthropogenic climate change: Improved Attribution of Climate Forcing to Emissions, written by scientists from NASA’s Goddard Institute including Drew Shindell and Gavin Schmidt.
Two especially notable points are made. Firstly, the researchers estimate that carbon dioxide (CO2) is ‘only’ responsible for 43% of observed warming, once interactions between gases and aerosols were taken into account. At the same time, methane accounts for 27% of warming, halocarbons 8%, black carbon 12%, and carbon monoxide and volatile organics 7%. Secondly, there are the policy implications that flow from this. Preventing CO2 emissions basically requires reducing deforestation and the burning of fossil fuels – with the latter being an especially challenging thing to do in a world as promiscuous with energy as ours. Reducing methane, by contrast, may be as simple as capturing and burning gases from landfills, and adopting other comparatively low-cost and low-sacrifice strategies. The authors conclude that strategies that incorporate all greenhouse gases (GHGs) are “likely to be much more cost-effective than CO2-only strategies.”
There are other complications involving GHGs, including atmospheric lifetime. CO2 is removed by various means, across different timescales. Methane doesn’t last as long, but does cause more warming than CO2 when present and often breaks down into it later. Black carbon is washed out of the atmosphere quite quickly, meaning that eliminating its production could yield reduced radiative forcing relatively quickly.
The greater importance of non-CO2 gases described in this study is potentially good news for climate change mitigation, given how challenging it has been to convince governments to accept even very minor costs in order to reduce the risks associated with climate change. Developing an improved understanding of exactly how much various GHGs alter the climate should also allow for more efficient carbon pricing, where the incentives to reduce the most harmful GHGs are the strongest.