Climate change turned up India's heat. But by how much?

An Indian worker displays air coolers for sale in New Delhi, on April 28, 2022. PHOTO: EPA-EFE

NEW YORK (BLOOMBERG) - India this year experienced its hottest March in 12 decades of records, and one of its driest. Next came the third-hottest April, after 2010 and 2016. Then it got even hotter.

New Delhi saw an average maximum April temperature of 40.2 degrees Celsius, according to the Times of India. The heat is jeopardising the country's wheat supply, just as Russia's war in Ukraine disrupted trade from Eastern Europe. Temperatures in neighbouring Pakistan's Jacobabad rose to 47 degrees Celsius.

The worst of the heat wave has now abated, according to the India Meteorological Department. Scientists are already investigating the extent to which carbon dioxide from power plants, cars and the rest of the fossil fuel economy worsened the devastation.

Global temperatures have climbed 1.2 degree Celsius since the mid-19th century. So when someone asks the question, "Did climate change make this or that heat wave hotter?" the answer is almost invariably yes.

"The number of heat waves is directly in response to global warming," says Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology who has looked at 70 years of data. Analysing decades of heat data is different from asking about one hot spell in particular - and looking for answers about India's heat is harder than most anywhere else in the world.

Agriculture accounts for 18 per cent of India's economy and employs more than half of its workforce, so accurately predicting the monsoon is of critical national interest. But the country's geography - northern plains bound by the Himalayas and the Tibetan Plateau - make forecasting difficult, especially given that monsoons are already prone to variations in timing.

Researching the effects of warming on India is made harder still because global climate models built in developed countries have failed to adequately account for unique factors in South Asia. That's complicated efforts to understand local effects of global carbon dioxide pollution.

Recent work by the Indian Institute of Tropical Meteorology, in Pune, has made progress by adapting the US's Climate Forecast System to the region.

"Our weather inherently is hard to predict," says Arpita Mondal, a climate researcher at the Indian Institute of Technology Bombay. Climate is basically an average of a region's weather. "India is really unique."

India's pollution and water use patterns differ from developed nations in ways that have also created puzzles for researchers. Small sulfur particles called aerosols, which result from burning coal, tend to scatter incoming sunlight and cool the skies a bit all over the world. But there are also aerosols made of soot and dust that have the opposite effect. These particles attract sunlight and result in more warming. Mondal's work has shown that India's aerosols may include more of the heat-attracting variety than scientists previously thought.

Water matters, too, and not just because humidity combined with heat can be a deadly threat to human life. Evaporation from massive irrigation can cool soils and dampen regional temperatures. But the potential cooling effects of evaporation in India are now being reconsidered under closer scrutiny.

This means two features assumed to mask human-caused heating in India may be weaker than previously thought. Scientists may consequently have underplayed the climate's role in warming the area.

People cool off in a wave pool during a hot summer day at a water park in New Delhi on April 30, 2022. PHOTO: AFP

When researchers at World Weather Attribution, a project that untangles the climate influence on extreme weather, examined a deadly 2016 heat wave in northwestern India, they found that peak daily temperatures didn't carry a strong climate signal. The result may have been based, in part, on the overstated cooling effects from aerosols and evaporation. This time it's different.

"What seems remarkable, or really extreme, is that it has been hot for so long. Basically the whole pre-monsoon season has been exceptionally hot," says Friederike Otto, a senior lecturer in climate science at Imperial College London and head of World Weather Attribution. "But the really, extremely high temperatures have been measured in the last few days. So a big question is, 'What is the right way of looking at this event?'"

Her team has already launched a new analysis of this year's heat in India, and, as it does at the start of any study, will evaluate the best questions to ask about a heat wave of such complexity. Many heat waves, including the record-shattering spell over the western US-Canada border in 2021, are best evaluated by their highest temperatures on a day or span of days.

The current heat event in South Asian poses an additional challenge because of its duration - its length may suggest more similarities to the six-month Siberian heat wave in 2020. World Weather Attribution's research concluded the Siberian heat was made more than 600 times likelier by greenhouse gas pollution.

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Attribution studies are often produced within days or weeks of an extreme event. A critical element of this expedited research is to highlight the plight of people experiencing a climate disaster, allowing leaders and citizens to make better decisions in a time of crisis. In the long run, attribution research can inform how societies adapt to a warming world - a process still in its infancy.

Ahmedabad, a city of 8 million in the western state of Gujarat, first released a heat action plan and warning system in 2013, three years after a heat disaster killed 1,300 people in a month. Others have followed, and now India is working with more than 130 cities and districts to develop similar plans. Better understanding the link between climate change and the latest heat wave might push that process forward.

"With all this international attention on this event," Mondal says, "maybe this will be recognised as a disaster and some policy level interventions will come about both at the federal and state levels."

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