3rd February 2012.
Actions to combat global warming are frequently cast by climate-change deniers as absurdly expensive, impractical, or unlikely to make any tangible difference in a time-scale meaningful to humans. However, a comprehensive new study has identified a range of practical and economically viable measures that are shown both to mitigate near-term climate change and to improve human health and food security (Shindell et al., 2012).
The starting point for this work is that tropospheric ozone and black carbon (BC) are known to degrade air quality and to cause warming, thus actions to reduce amounts of these agents promise multiple benefits. Methane enters the equation as a precursor of ozone and in its own right as a powerful greenhouse gas with a relatively short atmospheric lifespan.
Using the IIASA-GAINS* model, the authors narrowed down ~400 existing pollution control measures to 14 options, all based on current technologies, which have the combined potential to achieve nearly 90% of the maximum modelled net GWP reduction. Of these, seven target methane emissions. MethaneNet members who attended our ‘Methane Hack’ meeting at the Geological Society last December will already by familiar with these mitigation options, which cover coal mining, oil and gas production and transport, waste and landfills, waste water, livestock manure and rice paddies.
Based on the 14 prioritised measures, the authors modelled future emissions scenarios and, using the ECHAM5-HAMMOZ and GISS-PUCCINI three dimensional composition climate models, calculated their warming impact. The impacts on health and agriculture were calculated separately. Overall, the work demonstrates that the 14 measures could significantly reduce the global mean temperature over the next two decades, although the authors emphasise that only when the methane and BC measures are combined with actions to mitigate CO2 emissions is the target of limiting the global temperature increase to less than 2°C achieved. The methane control measures contribute more than half the warming mitigation with the lowest associated uncertainties.
Finally, a cost and benefits valuation based on the VSL (value of a statistical life), world prices for crops and the SCC (social cost of carbon) was conducted. The figures calculated are highly dependent on the time span considered and the discount rate. However, even a conservative selection of the metrics used indicates that the benefits of implementing these methane and BC abatement measures far outweigh the costs.
The study also considered the impacts of the 14 control measures by region and sector. The greatest benefit arises from controlling methane emissions from fossil fuel extraction and transportation. The single most significant measure would be to tackle methane emissions from Chinese coal mines.
Professor David Fowler of the Centre for Hydrology and Ecology sums up this major study thus. “The strength of the approach is that there are many benefits and modest costs and if we compare what is possible with these measures against the glacial progress with control measures through UNFCCC, here we have some relatively quick wins. We still urgently need to control CO2 emissions, but the returns are longer term.”
*International Institute for Applied Systems Analysis Greenhouse gas and Air Pollution Interactions and Synergies
Drew Shindell, Johan C. I. Kuylenstierna, Elisabetta Vignati, Rita van Dingenen, Markus Amann, Zbigniew Klimont, Susan C. Anenberg, Nicholas Muller, Greet Janssens-Maenhout, Frank Raes, Joel Schwartz, Greg Faluvegi, Luca Pozzoli, Kaarle Kupiainen, Lena Höglund-Isaksson, Lisa Emberson, David Streets, V. Ramanathan, Kevin Hicks, N. T. Kim Oanh, George Milly, Martin Williams, Volodymyr Demkine, and David Fowler (2012). Simultaneously mitigating near-term climate change and improving human health and food security. Science, 335, 183-189.