Climate crisis behind heat extremes in India, UK: Study

Climate change is impacting global atmospheric circulation patterns making unprecedented heat extremes possible across the world, an international team of leading climate scientists who are part of the World Weather Attribution network said on Thursday.

WWA, which presented its analysis on the July UK heat wave spell on Friday said this (the spell) was made 10 times more likely due to climate change. Models analysed by the group show that the same event would have been at least 2 degrees C less hot in a 1.2 degree C cooler world or during pre-industrial times.

The rise in average global temperatures is changing atmospheric and global circulation patterns leading to a series of heat extremes this year in different parts of the world starting with the spring heat wave spell in India and Pakistan; the UK heat extreme in mid-July; and now extreme heat stress in the US, it added.

India and Pakistan’s March-April extreme heat spell was unprecedented, made about 30 times more likely because of human-caused climate change, a rapid attribution analysis by an international team of leading climate scientists who are part of the World Weather Attribution network said in May.

On July 18 and 19, an exceptional heat wave affected large parts of the UK. It was the first time that temperatures of 40 degree C and above were forecast in the UK according to WWA. On July 18, the mercury touched 40.3 degree C in Coningsby in Lincolnshire, breaking the previous maximum temperature record of 38.7 degree C, which was reached at Cambridge Botanic Garden on July 25, 2019. Overall, 46 stations met or exceeded the previous record stretching from Kent to north Yorkshire, and a temperature above 35 degree C was recorded in Scotland for the first time. Minimum temperatures were also extremely high with 25.8 degree C provisionally being recorded in Kenley in Surrey.

Like India’s heat spell which was followed by an extremely dry pre-monsoon season, the heatwave event in the UK was also very dry and followed a longer dry spell. July this year was the UK’s driest since 1911. Drought conditions have also been widespread across continental Europe in recent months, according to the report.

But the UK and India’s heat wave spell has been estimated to have a return period of around 100 years in today’s climate of 1.2C global warming making both unusually rare– 1 in a 100 year events. The impact of these events has been vastly different in the two countries. While at least 90 people have died in India and Pakistan as a result of the heatwave, a toll that will almost certainly increase substantially with more reporting, there are projections of excess mortality of over 840 people in UK for July 18 and 19 and increase in hospitalisations, infrastructure damage, and psychosocial effects. In India there were a number of indirect effects too. Extreme heat reduced India’s wheat crop yields, causing the government to stop wheat exports; shortage of coal led to power outages that limited access to cooling by affected people, the WWA analysis had said.

This year, parts of south Asia, large parts of Europe and very recently the US has also reported extreme heat. More than 85 million Americans are under excessive heat warnings or heat advisories issued by the National Weather Service. Excessive heat, severe storms and flooding are all expected this week, Al Jazeera reported on July 25.

“The heatwave in the UK occurred as part of a large Western European heat wave generated by high pressure over Central and Western Europe and very warm air flowing in from North Africa. While the heat was only very extreme for the two days of the 18th & 19th of July in the UK, other parts of Western and Southern Europe experienced more prolonged heat,” said WWA’s report released on Friday.

Climate scientists said all of these heat extremes that posed a massive public health crisis were linked by certain global atmospheric patterns. “The heat wave event in Western Europe was driven by a high-pressure system called the Azore’s High. It was also the hot, dry winds that came from Sahara. Most of the drivers that drove the South Asian heat wave was mostly attributed to weak westerly disturbance as well as a heat dome situation over much of South Asia but what is consistent between both these events is that the temperatures, we are seeing this year are very high. The differences in extremes that we can see can be attributed to climate change. With rise in temperatures in different global regions, we can expect an increase in frequency of heat extremes and magnitude. The magnitudes can be strongly linked to climate change. Climate change can impact different drivers differently,” said Mariam Zachariah, climate scientist at Imperial College London, member of WWA.

“It is very interesting that this is happening in the La Nina year which is associated with cooler climate. The Indian and European heat waves are definitely linked. One theory is that it may be because of the Rossby waves. They originate in the Antarctic and come down to central Asia, Europe etc. Sometimes they can also become stagnant creating an area of high pressure which can cause a sinking of the atmosphere and extreme heat. These large-scale atmospheric features are, of course, linked to climate change. There is no denying that. But various local factors also influence the intensity of their impact. For example, our pre-monsoon rains were also scanty and the soil was dry which led to positive feedback of heat,” explained M Rajeevan, former secretary, ministry of earth sciences.

“We have one atmosphere. These events are influenced by the global circulation pattern and affected by certain regional and local parameters. The changing behaviour of the jet stream influences heat waves in the extra-tropics but in tropical countries like India there are other factors too,” said M Mohapatra, director general of IMD.

This year, India recorded the highest number of heat wave days since 2011 according to data presented by the ministry of earth sciences in Lok Sabha on Wednesday. India recorded 203 heat wave days this year, followed by 201 days in 2012 and 174 in 2019. Haryana, Punjab, Rajasthan, Uttarakhand, Delhi recorded the highest heat wave days in the past ten years with Delhi recording 17 heat wave days and the rest recording over 20 such days.