Sankar Ray
Pray do not underestimate the methane question
Atmospheric physicist, Prabir K. Patra: any effort toward reduction of carbon dioxide and methane emissions improves the living conditions of Indian citizens and contributes to the global effort to mitigate climate change
This article first appeared in the April-May 2017 issue of Farmers' Forum magazine.
The big debate in the farming sector is about climate change proofing agriculture. Indian agriculture is particularly vulnerable to climate change and future proofing India’s food security would mean addressing Indian farming’s exposure to global and domestic environmental change and building capacity to manage its onslaught. An even more fundamental question is about how Indian agriculture itself is contributing to climate change. Is the only danger from CO2 emissions or are there other potent threats?
Consider rice, amongst India’s most widely grown crops. Rice varieties are known to affect greenhouse gas emissions, especially methane. “The physiology of rice plants regulates methane emissions by making available sources of methanogenic substrates through carbon in the roots, including exudates, and also by transporting CH4 emissions through the aerenchyma.1 Several studies have confirmed variations in the emission levels of different rice cultivars”. How serious is the issue?
Prabir K. Patra, winner of the MSJ Horiuchi Award (2016), speaks to Sankar Ray, for Farmers’ Forum, on the methane-farming connect.
Sankar Ray (SR): Is the threat from methane potentially much greater than that from CO2?
Prabir K. Patra (PP): Methane (CH4) is one of the most important short-lived climate forcers (SLCFs) along with tropospheric ozone and black carbon, according to the United Nations Environment Programme. Reducing their emissions could improve public health, reduce losses in crop-yield and slow the rate of near-term climate change (UNEP 2011). Methane has duel role in the earth’s atmosphere:
- A very strong greenhouse gas, with global warming potential (GWP) of 23 over 100 years (IPCC). GWP is a measure of heat (earth’s outgoing radiation) trapped by 1 kg of CH4 relative to the heat trapped by 1 kg of carbon dioxide.
- It takes part in tropospheric chemistry, leading to ozone production. Since methane reacts with hydroxyl (OH) and other radicals, it has a residence time of only 10 years once emitted to the atmosphere (unlike that of CO2, which is chemically inert in troposphere and thus resides longer than 100 years in atmosphere). This means if CH4 emissions are reduced today, we will reap the benefits in 10 year, but benefits of CO2 emission reduction today will be seen after 100 years.
The shorter lifetime of CH4 makes it attractive for policymaking because by reducing a smaller amount of CH4 we make greater and quicker impact on global warming (— 23 times compared to CO2). Many methane sources owe themselves to mismanagements of waste, quality of feeds to the livestocks and such others. So the quality of life of every citizen improves when we take measures for reducing CH4 emissions by improved management practices.
The shorter lifetime of methane makes it attractive for policymaking because by reducing a smaller amount of methane we make greater and quicker impact on global warming (23 times compared to CO2).
SR: Do we tend to underestimate the methane question?
PP: In the science community CH4 means a lot of opportunity but I agree with you that methane is not often discussed in some of the important fora. That is probably because methane concentration is only about 1.8 ppm today compared to about 400 ppm of CO2. For the scientific community, prediction of year-to-year variability in CH4 concentrations has also remained as one of the most challenging.
In our paper (Patra et al., Biogeoscience, 2013) we showed that when we weigh CH4 emissions with the global warming potential, CH4 radiative forcing become higher than that from all fossil-fuel CO2 emissions from the South Asia region. We estimated average CH4 emissions of 37 Tg-C/yr and best estimate of CO2 emissions of 297 Tg-C/ yr (1Tg = 1trillion g), which means the net global warming effect of CH4 emission from South Asia (37 x 23 = 851 TgC/yr in CO2-equivalent) is way greater than the fossil fuel CO2 emission.
SR: Agreed that the atmosphere is under threat but is there any reason to panic?
PP: I think there are reasons to panic, considering our future generations. I am worried about the high level of air pollution in India and the South Asia region in general – as I said CH4 plays a role in air pollution chemistry. We do not want to get this worse. There are many kind of illness just due to poor air quality (respiratory, cardiovascular...).
This can be achieved by educating people that everyone can live better and at the same time reduce greenhouse gases emission. For example, (a) driving well-maintained vehicles on the road reduces CO2 emissions, reduces air pollution, (b) Reduction of CO2 emission and air pollution can also be achieved by proper driving of vehicle, say lane driving, smooth transition of speed.
On the longer time scale, the effects of greenhouse gases on regional climate change is lesser known but the earth system with high global warming is likely to be irreversible. It is always better to keep our living (environmental) conditions as close to the natural state as possible. A warmer world (which is guaranteed as greenhouse gases continue to increase in atmosphere) is definitely not desirable for Indians – we already invest so much on air conditioning.
SR: What are the main threats facing Indian farming today from the climate change perspective?
PP: Several studies have shown growing-season mean temperature and precipitation are very important for crop yield. For example, if there is an increase in temperature during the winter months, the yield of wheat is affected and we all know the control of rainfall on rice yield. There are also studies that air pollution, such as high ozone (O3) level reduce productivity of many crops, such as wheat, soybean and rice.
In our paper we showed that when we weigh methane emissions with the global warming potential, methane radiative forcing become higher than that from all fossil-fuel CO2 emissions from the South Asia region.
SR: In what manner is Indian agriculture itself contributing to this threat?
PP: Methane (CH4), which is a precursor of ozone production, is emitted from rice cultivation, enteric fermentation (ruminants), manure and waste management. So it is clear that emission of CH4 has a negative feedback on crop yield. Nitrous oxide (N2O) is another strong greenhouse gas that emits from our agricultural system.
With the advent of measurement and modelling, we are now able to estimate and verify emissions of CH4 from different parts of the globe (Patra et al., J. Meteorol. Soc. Jpn., 2016). The South Asia region is one of the hottest spot in the world as far as emission of CH4 is concerned. Further investment in research is needed for clear separation of different emission sectors so that effective policy decisions by the national government can be taken.
SR: What are the policy changes that the government of India should be considering to mitigate these threats?
PP: One of our studies (funded by the Ministry of Environment, Japan) is now looking into emission reduction potential of CH4 by changing agricultural practices, such as selection of rice cultivars, continuous flooding vs intermittent flooding, application of fertilizers. Apparently, the intermittent flooding method has been implemented in many areas of Japan and China in order to reduce CH4 emissions from paddy fields. In fact, this method can also save water by a large margin but is possible to implement without risking the crop damage but can only be envisioned when highly secured irrigation facility is available.
SR: What policies should India and the world keep in mind to drive change?
PP: Carbon dioxide plays the major role in global warming and methane has the second largest contribution to the global warming due to anthropogenic emissions. As mentioned earlier, a couple of factors make emission reduction of methane is the most attractive option for reducing impact of global warming and air (ozone) pollution. Apparently, any effort toward reduction of CO2 and CH4 emissions improves the living conditions of Indian citizens through direct reduction in air quality and preservation of water resources, and contributes to the global effort in mitigation of climate change.
Prabir K. Patra, an atmospheric physicist of global repute, is senior scientist at the Department of Environmental Geochemical Cycle Research, Yokohama, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and formerly head of international research project on climate change at the Frontier Research Centre for Global Change. His research paper has been published in many peerreviewed journals, including Nature.