Simultaneously Mitigating Near-Term Climate Change and Improving Human Health and Food Security

Atmospheric pollutants such as carbon dioxide, black carbon, and methane contribute to degrading air quality, global warming, and negative health impacts.  Although there currently exist over 400 emission control measures, no research has been done comparing these measures with each other and their effect over long periods of time.  Shindell et al (2012) examined a number of these control measures using projection models to see the effects of these measures based on a projection of the future, and compared results between the control measures.  Using various models the authors calculated projections for future temperatures based on each emission control measure and the impacts of measures on climate, agriculture, health and economic valuation.  The results of the models showed that the measures could reduce global mean temperature increase over the next few decades and could reduce crop yield losses, premature deaths, and ice cap melting.  Although the tested models do not deal with carbon dioxide emissions (a larger long term contributor to global warming than methane or black carbon as it persists longer in the environment), the authors of this paper hope that the widespread benefits of their studied measures will help convince policymakers to adopt these measures.-Anthony Li
Shindell D., Kuylenstierna J. C. I., Vignati E., van Dingenen R., Amann M., Klimont Z., Anenberg S. C., Muller N., Janssens-Maenhout G., Raes F., Schwartz J., Faluvegi G., Pozzoli L., Kupiainen K., Hoglund-Isaksson L., Emberson L., Streets D., Ramanathan V., Hicks K., Oanh N. T. K., Milly G., Williams M., Demkine V., Fowler D. 2012. Simultaneously mitigating near-term climate change and improving human health and food security.  Science 335, 183

The researchers used the International Institute for Applied Systems Analysis Greenhouse Gas and Air Pollution Interactions and Synergies (IIASA GAINS) model and selected 14 pollution control measures out of its 400 that focused on mitigating climate change, enhancing air quality, reducing methane, and technical and regulatory measures referred to as black carbon measures.  Technical measures included removing diesel vehicles, biomass stoves, brick kilns, and coke ovens, while regulatory measures included bans on particular pollution sources and providing modern heating and cooking technologies. The IIASA GAINS model estimates worldwide emissions reductions of particulate and gaseous species based on real-world data and subsequent measures that have already been applied.  The selected pollution control measures were then applied to a projection of future atmospheric composition based on energy and fuel projections, regional and global livestock projections, and all presently agreed upon emission-related policies, which was all provided by the International Energy Agency.  The projection was set at multiple scenarios, using combinations of measures or individual measures and seeing their subsequent effects.  Emissions from these scenarios were also used with the ECHAM5-HAMMOZ and GISS-PUCCINI composition models to calculate the impacts on atmospheric concentrations and radiative forcing, both of which could add to uncertainty in the temperature predictions.  Once the projections were completed, the authors then analyzed the separate packages of measures based on physical impacts (including avoided warming, avoided crop yield losses, and avoided premature deaths) and valuation per metric ton as calculated by the value of a statistical life.
The authors found that of the projected measures, the scenario where all methane, black carbon, and carbon dioxide control measures are used had the lowest increase in temperature.  The methane with all the black carbon measures scenario and the carbon dioxide measure scenario both came in with the second lowest increase, followed by the methane and black carbon technical measures scenario and the methane measures only scenario.  The ECHAM and GISS models calculated a negative forcing for all the measures.  Analyzing the individual packages of the measure’s effects show that methane control measures resulted in the most avoided warming, most avoided annual crop yield loss, and highest value in climate and crops of US dollars per metric ton of methane.  The black carbon technical measures had the highest amount of annual avoided premature deaths and highest value in health at US dollars per metric ton of methane.
The researchers found that the measures were capable of substantially reducing the global mean temperature.  Specifically, they targeted the black carbon measures and said the results showed how these measures can be used to reduce drought risk in Southern Europe and the Sahel while reversing shifting monsoon patterns in South Asia.  In terms of agriculture, the methane and black carbon technical measures showed great reduction in crop yield loss, while the black carbon regulatory measures had minimal impact.  Health impacts were vastly improved upon with both of the black carbon measures, as black carbon contains particles smaller than 2.5 micrometers which are much more damaging to health than ground level methane is. 

Only a small fraction of air quality measures currently implemented provide substantial mitigation against global warming.  However, the methane and black carbon emissions reduction measures studied in this paper show that these measures could have global and regional impacts on climate, as well as human health and agriculture.  The authors of this paper hope that the measures benefitting not only climate change but also health and agriculture will help motivate policies to put them into practice.

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