For the first time, scientists have shown that greenhouse gases released by human activities are solely responsible for the warming climate in India
NEW DELHI – Scientists have for the first time shown that greenhouse gases (GHGs) released by human activities are solely responsible for the warming climate in India, where average temperatures have risen by as much as half a degree in five decades.
Alarmingly, the researchers found that the warming caused by GHGs across India was more than three times what was actually observed during this period. That the warming was confined to 0.5 degree Celsius was due to the cooling effects of pollution, another by-product of the use of fossil fuels.
The findings by IIT Delhi scientists were published on Tuesday in Scientific Reports, a journal of the Nature Group. For the study, the researchers looked at temperatures from 1956 to 2005.
“Our main finding is that greenhouse gases have raised India’s temperatures much more than what we have experienced but it has been offset substantially by aerosols and land use change. Importantly, there was no contribution to warming from natural causes,” said IIT professor Krishna AchutaRao, who co-authored the study.
While warming is a worldwide trend that has been scientifically linked to GHG emissions, this is the first study to trace the cause of rising temperatures in India to such emissions.
The IIT research has crucial implications for the fight against air pollution. “The findings suggest that there could be a sharper increase in warming as we reduce air pollution,” AchutaRao said.
According to the models used by AchutaRao and other authors, the warming contributed by natural factors was just 0.005 degree C, while GHGs caused about 1.85 degree C warming.
The pollution and land use change was seen to have led to a cooling of 1.2 degrees C, resulting in about 0.65 degree C net warming. This compared well with the observed warming of about 0.5 degree C.
The IIT study found the sharpest rise in temperatures in the western Himalayas, specifically J&K and adjoining areas. It found that GHGs accounted for a warming of as much as 3 degrees Celsius during the 50-year period.
“Other anthropogenic factors” (pollution, land use change) offset this rise by 1.5 degrees C, resulting in a net rise of 1.5 degrees.
Western Himalayas was among the seven homogeneous temperature regions in the country the researchers looked at. The others were east coast, west coast, interior peninsula, northwest India, northeast and north-central India.
Northeast and north-central India were the only regions that showed no significant warming during the period under study.
The authors – Dileepkumar R, AchutaRao and T Arulalan – used two observational temperature datasets together with results from a multi-model archive of forced and unforced simulations. They estimated the contribution of natural and anthropogenic (human-caused) influences through a two-signal optimal fingerprinting analysis.
The study further isolated the anthropogenic influences due to GHGs from other human-induced factors to arrive at their results.
“We can attribute surface temperature changes over India between 1956 and 2005 to anthropogenic forcing mostly by greenhouse gases and partially offset by other anthropogenic forcings including aerosols and land use land cover change,” the study concluded.
