Explained: How climate change is linked to heatwave as mercury breaches 49 degree mark in north India

The United Nations Intergovernmental Panel on Climate Change warns that heat waves and humidity-related heat stress will intensify in South Asia, and scientists who study climate change say Indians can expect more of the same hot temperatures in the coming years. (Image: AP)

India has been reeling under what experts say is the worst heatwave in its history, with scorching day temperatures being reported in many states in the past two weeks.

March was recorded as the hottest in 122 years from 1901-2022, according to reports. April brought no respite either, with Northwest and Central India being the hottest.  Overall, it was the fourth hottest April the country has witnessed ever since records were kept. Several places recorded maximum day temperatures in the range of 44-46°C for several consecutive days, while a few places even touched the 47°C mark. Worse, on May 15, some parts of Delhi and Uttar Pradesh recorded a high of 49 degrees Celsius. The mercury, however, dipped slightly on May 16.

There have been studies that said that March and April are warming much faster than the core summer months of May and June in India. The persistent heatwave has highlighted global warming’s cascading effect on the temperature, according to inputs share by Climate Trends, India, a climate communications initiative.

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Climate change is not only raising temperatures and making India’s heatwaves more intense, it is also changing weather patterns that, in turn, are driving dangerous heat extremes, say experts. This is resulting in the cooling western disturbance being disrupted, anticyclones becoming more dominant, and Arctic waves breaking records, among other things.

Impact on western disturbances

A term used often in weather-related information, ‘Western Disturbances’ refers to storms that originate in the Caspian or Mediterranean Sea, bringing non-monsoonal rainfall to northwest India and parts of Central India. Simply put, these disturbances govern the wind pattern over the mountains and plains. In the summer, these disturbances are known to suppress heat wave conditions in the Indo-Gangetic plains.

However, the climate change has led to dynamic changes in the pattern of western disturbances, according to experts. Although the frequency of the disturbances has increased, they have not translated to the precipitation associated with them.

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“Western disturbances are getting lighter by virtue of increasing heat, as it decreases the moisture content. Subsequently, these disturbances are now moving across higher elevation due to heat and are reaching up to the Karakoram range. Climate change has made some dynamic changes in the pattern of the western disturbance,” said AP Dimri, director, Indian Institute of Geomagnetism, Maharashtra.

The anticyclone

The large-scale circulation of winds around a central region of high atmospheric pressure is called an anticyclone. While a cyclone attracts the winds around it, an anticyclone throws the winds in all directions as it rotates clockwise. Usually, anticyclones develop over Northwest India during the summer. But, the longer persistence of these anticyclones has exaggerated the heatwave conditions, experts said explaining another indirect impact of climate change on the heat wave.

“The anticyclone sent warm winds from north-west to central and western India for a longer duration, causing as well as intensifying the heat wave. In the absence of rains, the desert region was already witnessing high temperatures,” says Mahesh Palawat, vice president, Meteorology and Climate Change, Skymet Weather.

The Arctic heat wave 

Arctic heat waves have been breaking records, with the annually averaged Arctic near-surface air temperature increasing by 3.1°C from 1971–2019, which is three times faster than the global average. Recent findings include increases in the frequency and intensity of rapid sea-ice loss events, melt events on the Greenland Ice Sheet, and wildfires.

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“Above-normal temperatures across the Arctic region are a major cause of concern as this directly impacts the circulations affecting the Asia region. Warming in the Arctic region pushes air upwards, leading to formation of a low-pressure area, which attracts the circulations in the sub-polar region. This has been the case this season. The intensifying Arctic heatwave pulled weather systems, including western disturbances, northwards, making them travel in higher latitudes and thus, it did not affect the weather over India,” explains Palawat.

The La Nina impact

La Nina (‘little girl’ in Spanish) is a climate phenomenon that cools the ocean surface on the tropical west coast of South America. In contrast, El Nino (‘little boy’ in Spanish) warms up the ocean surface in the equatorial region of the Pacific ocean. La Nina and El Nino jointly cause the El Nino-Southern Oscillation (ELSO), which is a weather and ocean-related phenomenon, that is also characterised by atmospheric pressure.

The La Nina is usually associated with intense winters and wet monsoons in India. While La Nina was earlier predicted to crash by the spring of 2022, it is far away from this.

“The north-south pressure pattern has been persisting over India, with La Nina extending its stay over the Pacific. This has definitely impacted the weather over India, which was seen even during the 1998-2000 period, when La Nina had persisted for three years,” says Raghu Murtugudde, Professor, department of atmospheric and oceanic science, University of Maryland.

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Sea surface temperatures continue to be well below normal in the tropical Pacific. This has helped La Nina survive through the spring season and rather extend, at least, until the arrival of the monsoon.

Worst yet to come?

According to the Ministry of Earth Sciences report ‘Assessment of Climate Change over the Indian Region’, the averaged frequency of summer heatwaves all India will increase to about 2.5 events per season by the mid-21st century (2040–2069), with a further slight rise to about 3.0 events by the end of 21st century (2070–2099) under the medium emission scenario.