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To fight climate change, reduce black carbon

In order to make our fight against climate change more efficient and economical, we need to address particulates like black carbon at the same time as we reduce carbon dioxide, finds a recent theoretical study from IISc.

One of the biggest topics of discussion at the the World Economic Forum at Davos this year was climate change. This has cemented the global consensus that not only is climate change real, but also a problem that we must collectively find a solution to. The problem at hand is, however, a gargantuan one. Carbon Dioxide and a dozen other Short-Lived Climate Pollutants (SLCP) have significant effects on global climate but they differ in how long they reside in the atmosphere. With so many issues at play, how does one prioritize our attack to best reduce the effects of climate change? A study by Dr. Ashwin Seshadri from the Divecha Centre for Climate Change, Indian Institute of Science, attempts to answer just that.

In a recent publication in Ecological Economics, Dr. Seshadri simulated global emissions of Carbon Dioxide and Black Carbon (and major SLCP) and looked at how we could reduce these two pollutants so as to keep the temperature rise within 2 degrees, while simultaneously minimizing cost. Dr. Seshadri did this by looking at a 'two-box climate model' that simulated atmospheric and oceanic temperatures in response to different levels of emission reduction efforts (or mitigation). These mitigation efforts were in turn converted to relative monetary costs. Costs of removing pollutants are generally lower at higher levels of pollution. (The cost increases when one has to remove fewer pollutants from a given volume of air.)

On running these models, it was found that the maximum global temperature was more susceptible to how long long-drawn our CO2 removal efforts were, and less so to how intense our efforts to remove Black Carbon (or BC) were. However, it was found that simultaneous BC removal would reduce our total mitigation expenditure. Others have shown that BC hampers human health and agricultural productivity and its removal costs lesser than that of CO2. Both these factors, coupled with the results of this study, point to the need to look seriously at BC removal without shifting the primary focus of our efforts from CO2.

“Air pollution and climate change are related”, said Dr. Seshadri. “Air pollution is an important issue in the current Indian context, and climate change will be increasingly significant in the coming years. It is important to look at what we can do to address both these problems in mitigating their effects.”

“This study was funded by the Divecha Centre for Climate Change, and it took about a year to complete. It is a purely conceptual, mathematical simulation, and there are relevant quantities – such as the mitigation cost factor – which we don't have estimates of. As of now I haven't collaborated with anyone working with carbon mitigation, but I am open to doing so if the right people come forward.”

“There are several interesting questions in this field that can be explored by young researchers”, added Dr. Seshadri. “One thing would be to look at regional effects using climate models. Regional effects of of Black Carbon and CO2 may look quantitatively different from the global average effects that were considered in this study. Multidisciplinary research does not have a tradition in India – so an individual researcher might have to pick a small, focused piece of a problem and explore that.”

This study shows that there is no escaping from the problem of dealing with CO2 emissions. If the reductions of CO2 turn out to be more expensive than we realize, we cannot replace it with more rapid reductions of some other warming agent such as Black Carbon – we have to go ahead and spend more to reduce CO2. We can however, minimize the total cost in the long run by reducing short-lived pollutants like Black Carbon as well.

Is better to slay the devil or to is it better to cross the deep blue sea? These difficult questions are best answered by science, and this study by Dr. Seshadri is one step towards chalking a roadmap for reducing global emissions.

About the study

The study was published online in the journal Ecological Economics earlier this month. It will be published in print in June 2015.

About the author

Ashwin Seshadri is at the Divecha Centre for Climate Change, IISc.

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