The potency of methane, a greenhouse gas, has been underestimated by nearly a third in global climate agreements like the Kyoto Protocol, say scientists at Columbia University and NASA’s Goddard Space Flight Center, US.

That miscalculation occurred because climate modelling studies — 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 impact India only if the terms of debate on climate change — arrived at in Kyoto, Japan, in 1990 — are altered to allow for the finding that aerosols 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 per cent from current estimates.

Policy experts involved with global climate change negotiations say that attempts, especially by the European Union, to link aerosols and greenhouse gas have been on the rise for 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 former secretary to the environment ministry.

Ghosh said the link was tenuous because the effect of aerosols is short-lived and can’t be compared to that of lingering greenhouse gases. “But these debates are going to surface repeatedly.”

Negotiations to allocate fresh pollution limits are expected to begin in December at Copenhagen, Denmark. India, facing international pressure on its current no-emission-cut-without-finance stance, has indicated significant policy shifts over the last few months and 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 (CO2). 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, long-term impact compared with methane.

Though CO2’s radiative forcing abilities may seem insignificant, it’s the most threatening as it is the most abundant greenhouse gas in the atmosphere.

Methane, in spite of being the second most prevalent greenhouse gas, is only about 0.4 per cent by volume of the total carbon dioxide present.

The inter-governmental panel on climate change puts methane’s radiative forcing at 0.48 watt per metre, or less than half the new estimates.

Drew Shindell, lead author of the study, said that though carbon dioxide is the big villain, methane’s much higher contributions can’t be ignored. “Aerosol impact on carbon dioxide is insignificant, but our study says methane’s contribution to warming, to date, is two-thirds of CO2,” 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 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 latest estimates from the environment ministry, methane emissions from the agriculture sector — the biggest source — rose 16 per cent between 1994 and 2000.

Other scientists, however, said 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 have been simplistic and so require several more analyses for validation,” said J. Srinivasan, professor, Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore.