New Delhi: The potency of methane, a greenhouse gas (GHG), has been underestimated by nearly a third in global climate agreements such as the Kyoto Protocol, say scientists at Columbia University and Nasa’s Goddard Space Flight Center in the US.
That miscalculation has occurred because climate modelling studies, which provide the scientific basis for limiting certain gases, have not accounted for the role of aerosols—fine particles suspended in the air—in driving global warming.
The findings are significant because scientists and experts in India say that including the effects of aerosols in global warming projections could make it tougher for Indian negotiators at climate talks. To be sure, this would affect India only if the terms of debate on climate change, arrived at in Kyoto, Japan, in 1997, are altered to allow for the research results’ findings that aerosols do indeed increase the potency of methane.
Today’s issue of Science reports that the scientists used computer model simulation to calculate, for the first time, the impact of various aerosols such as nitrous oxide emissions and sulphates, and raised methane’s global warming potential by about 30% from current estimates.
Policy experts who have been involved with global climate change negotiations say that attempts, especially by the European Union, to link aerosols and GHGs, have been on the rise for the past three years.
“That’s an emerging tactic and will undoubtedly spill over into future climate negotiations,” said Prodipto Ghosh, distinguished fellow, The Energy Research Institute, New Delhi, and a former secretary in India’s environment ministry.
Ghosh added the link was tenuous because the effects of aerosols were short-lived and couldn’t be compared to that of lingering GHGs. “Aerosols have limited local effects, so there are separate forums for that,” he said. “But these debates are going to surface repeatedly.”
Crucial negotiations to allocate fresh pollution limits are expected to begin in December at Copenhagen, Denmark. India, which faces international pressure on its current no-emission-cut-without-finance stance, has indicated significant policy shifts over the last few months and has committed to do its bit to keep the global temperature from rising more than 2 degrees Celsius by 2050.
Global warming potential indicates the role of a gas in heating up the atmosphere over time, relative to carbon dioxide. For instance, methane’s heat trapping or so-called radiative forcing abilities are 72 times greater than carbon dioxide over 20 years, but only 25 times as strong over a century. Contrastingly, nitrous oxide stokes global warming 289 times over 20 years and 298 times over 100 years, indicating a larger, longer term impact compared with methane.
Though carbon dioxide’s radiative forcing abilities may seem insignificant, it’s the most threatening by virtue of being the most abundant GHG in the atmosphere.
Methane, in spite of being the second most prevalent GHGs in the atmosphere, is only about 0.4% by volume of the total carbon dioxide present.
The Intergovernmental Panel on Climate Change puts methane’s radiative forcing at 0.48 watt per m, or less than half the new estimates.
Drew Shindell, lead author of the study, said that though carbon dioxide continues to be the big villain, methane’s much higher contributions means it can’t be ignored in forecasting future climate scenarios.
“Aerosol impact on carbon dioxide is insignificant, but our study says that methane’s contribution to warming, to date, is two-thirds of CO2 (carbon dioxide),” he said in response to an email questionnaire from Mint. “A stronger effect of methane emissions means that if future emissions go up, warming will be faster than projected, but if they go down, warming will be slower.” However, the authors didn’t quantify the increase in global temperatures over time as a result of methane’s increased contribution.
“That would depend on the scenario,” said Shindell. “However, with current aerosol levels, warming would indeed be faster where methane and carbon monoxide emissions increase.”
India’s dependence on agriculture and limited fuel efficiency norms for transport and industry make it a significant emitter of methane as well as aerosol pollutants such as diesel, sulphate and nitrate particulate matter.
According to the latest estimates from the ministry of environment and forests, methane emissions from India’s agriculture sector—the biggest source—have risen 16% between 1994 and 2000, from 300 million tonnes (mt) to 350 mt carbon dioxide equivalent. Emissions over a comparable period in the US went down from 615.8 to 591 mt.
Though countrywide aerosol loads over India are unquantified, the Asian Brown Cloud, or a haze of aerosol particles that looms over much of north India and China, and is blamed for a variety of climate effects from global cooling to erratic monsoon, are an indicator of the region’s aerosol contamination.
Other scientists, however, said that though the research report was important, more models were needed to validate the implications of the study. “Over the past few years, there have been other studies that have tried to link aerosols and global warming. Most of them have been too simplistic and so require several more analyses for validation,” said J. Srinivasan, professor, Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore.
Some studies, said Srinivasan, suggest that an increase in aerosols such as black carbon particles triggers a rise in temperature. But in California, reduced levels of black carbon caused temperatures to rise, he added. “So the jury is still out.”