Temperature rise more in winter months than in summer

PUNE: The warmth of winter months has increased significantly over the past 100 years.

Data of the India Meteorological Department (IMD) for the past 114 years revealed that the increase in temperature had been more in the winter months than those of summer. The highest rise in maximum temperature has been in December and February, followed by November and October.

The average maximum temperature of December and February has increased by 1.5°C over these years, the data showed. November has become warmer by 1.4°C and the maximum temperature of October has increased by 1.1°C.

"Results show significant warming in all seasons, but more so in the colder months," said Arvind Kumar Srivastava, the director of National Climate Centre, IMD.

An earlier research - 'Updated analyses of temperature and precipitation extreme indices since the beginning of the 20th century: The HadEX2 dataset' - in 2012 by climate researchers from across the world, including Srivastava, had revealed widespread changes in temperature extremes consistent with warming over the last 110 years. Trends were stronger in more recent decades.

Referring to the latest study, Srivastava said: "The highest rise in mean temperature in India over this period has been in post-monsoon or colder months of November and December - by 1°C. Winter month February and post-monsoon month October followed them. The annual mean temperature of the country has increased by 0.6°C. The rise in mean and maximum temperature in each decade since 1901 has been continuous," said Srivastava.

The annual mean temperature refers to the average temperature for the entire year at a location. According to IMD, the post-monsoon season runs from October to December in India, while winter from January to February.

The highest rise in maximum temperature over the last 114 years has been in December and February, followed by November and October. The exact reason for the phenomenon in the colder months is debatable though a section of researchers from across the globe attribute the temperature rise over the years to global warming caused by anthropogenic activities.

"The atmosphere is stable in most parts of the northern hemisphere during the winter months. As a result, the impact of anthropogenic pollutants is more pronounced. This may be causing more warming in winter months," said Srivastava.

A senior scientist of Indian Institute of Tropical Meteorology (IITM) said, "The warming trend has been noticed in all the months, but more so in post-monsoon and winter months. A research we conducted in 2002 had revealed an increase in absorption of aerosols from emissions during the pre-monsoon months. It could be actually cutting down the solar radiation reaching the earth's surface, causing reduced warming during pre-monsoon or summer months as compared to post-monsoon and winter months. The concentration of aerosols is more in pre-monsoon months than during monsoon and post-monsoon months."

Hot October

On the unbearable heat this October, Srivastava had an interesting take from the study: the October mean temperature (the average of maximum and minimum temperatures) in India has increased by 0.66°C in the last 114 years.

Though not a reason for the rise in temperature over the last 114 years, the unusually hot October this year could be attributed to the truant clouds and anti-cyclones over the northern and central parts of the country, Srivastava said. "Anti-cyclones are associated with subsiding air, causing warming of the atmosphere. The subsiding air suppresses cloud formation. Sun's radiation directly reaches the earth's surface in less cloud," Srivastava said.