Gangasagar pilgrims try to keep warm in Calcutta. (Reuters)

The current winter in Calcutta is one of the chilliest in memory with the temperature plummeting to 10.8 degrees Celsius on December 28. Weathermen think the mercury may dip further. Though Calcutta has witnessed a colder January — 8.4 degrees Celsius in 1989 — a below 11 degrees Celsius December temperature is rare.

Does the chill counter the theories of climate change and global warming?

“Definitely not. It actually vindicates the theory of climate change; one has to understand that climate change and global warming are not synonymous. Warming is just one expression of climate change,” says Jadavpur University professor Jayshree Roy.

According to her, climate variability is actually leading to weather extremes, which means warm days are becoming warmer, rainy days bring more rain and cold days are becoming colder.

Scientists warn that short-term variations in weather patterns should not be used to disprove theories on global warming. Weather is dependent on a host of factors, including currents like El Nino and Arctic Oscillation.

There are other theories about winters becoming colder. Many scientists believe that the activity of the sun is linked to the appearance of sunspots which are dark, cool patches on the sun’s surface that come and go in roughly 11-year cycles. It has been observed that while warmer climate is linked to higher sun activity, the opposite applies for cooler conditions.

The appearance of the “little ice age” in the 17th century is attributed to the absence of sunspots. In the 20th century, the sun was unusually active, peaking in the 1950s and the late1980s. But around the turn of the century, the sun’s activity declined and the rise in the earth’s temperature began to slow and has now been constant for the past few years.