Updated: May 31, 2022 11:33:30 am
The record warm temperatures in April provide an example of how global warming can combine with natural variability to produce record heat waves. This spring portends yet again that higher frequency, duration, intensity and area covered by such heatwaves are expected in these regions with continued warming — not only locally but also because of the Indian Ocean and the Arctic.
Over the last few decades, Pakistan, the Middle East, and the Mediterranean have been hotspots for warming. Over the 1990-2020 period, this is well above 1 degree Celsius over this region while over India it is relatively lower. The heatwaves during the spring months, referred to as the pre-monsoon season over India, can be expected via the high-latitude planetary waves diving down into the Indian subcontinent along with the western disturbances. But the spring season has also become extreme now with excess rains and locust attacks, pre-monsoon cyclones, and severe pre-monsoon rainfall deficits. This year’s record-breaking heatwaves are part of this spectrum of extremes global warming can produce over this region.
Global warming is loading the dice as expected – from once in a decade, heatwaves are occurring about once in three years and once in 50-year events are occurring about once in a decade. The intensity and duration of the heatwaves have also trended up over South Asia and the areas covered by heat waves have increased substantially. The latest IPCC report assigns a high confidence to the detection of increasing extreme temperatures over South Asia.
The other hammer swinging over this region is the impact of a La Niña-like warming pattern, that is, a slower warming over the eastern tropical Pacific around the Galapagos compared to the relatively faster warming over the western Pacific around New Guinea and the Indonesian Seas. The unusual persistence of La Niña into the third consecutive year is expected in 2022, providing a clear example that the future is already here – natural variability and global warming combining to amplify natural hazards like heat waves over South Asia.
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During a La Niña winter, a north-south pressure pattern sets up over India, which can funnel in bitterly cold temperatures far down into peninsular India unlike during an El Niño winter when the cold blast of air tends to be more confined to the north. The persistence of the La Niña pressure pattern into spring has been driving the unprecedented dust storm and heatwaves far south into the western coast of India. The much warmer than normal temperatures over Central Asia and Eastern Europe were associated with colder than normal temperatures over the Indian Subcontinent during December 2021 into February 2022 giving India a cold winter. But the surface temperatures flipped to a much warmer anomaly over the Indian Subcontinent extending into the Middle East and a cold anomaly over Central Asia and Eastern Europe. The associated low-pressure anomaly over the Indian Subcontinent has been inviting westerly winds and the blast of hot air from the Middle East into Pakistan and India. The La Niña pressure pattern has been splitting the hot air over the Arabian Sea south into western India and north into Pakistan and northern India. The record pre-monsoon rainfall deficits have accompanied the deadly heatwaves.
The bad news, of course, is that the La Niña-like pattern is expected to continue under global warming and may produce more such spring heatwaves. Additional amplification of the misery may come from excess pre-monsoon rainfalls with unusual hazards such as the locust attacks or agricultural and ecological droughts during the pre-monsoon.
The monsoon season may arrive on time and bring normal rains due to the expected continuation of the La Niña to cool much of India by July. Pakistan has to wait till the end of July to cool down. However, the North Indian Ocean has to pass through the pre-monsoon cyclone season before the monsoon. The number of cyclones and their rapid intensification are worrisome due to the weaker monsoon circulation associated with global warming.
Relentlessly warming temperatures over land and the Indian Ocean are combining with warming over the Arctic to produce decreasing rainfall over both India and Pakistan. The region is a poster child for all that can go wrong with global warming — floods, droughts, sea-level rise, heatwaves, extreme rainfall, and agricultural and ecological droughts. Negative health outcomes are expected in warm regions which favour the growth of human pathogens and wet seasons which spread diseases.
This geopolitically-sensitive region is highly vulnerable to climate change and can become more resilient only with well-coordinated mitigation, adaptation, and early warning systems. The early heatwaves of spring 2022 will hopefully serve as another reminder of the need for cooperation on climate action in the region.
This column first appeared in the print edition on May 6, 2022, under the title ‘Heat wave, red flag’. The writer is professor of Atmospheric and Oceanic Science and Earth System Science at the University of Maryland and visiting faculty at Indian Institute of Technology, Bombay
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