Climate change more robust now, La Niña may not be effective in warmer future : Scientists

New Delhi: Climate change is growing stronger and more robust, and the cooling, counter effects of La Nina may not be effective in a warmer future, climate scientists said, assessing current heat trends seen in large parts of the country.

The India Meteorological Department (IMD) has predicted an early summer this year, with above-normal temperatures and intense, long heatwave spells.

The country experienced its warmest February since 1901, with the fifth lowest rainfall since 2001, it said.

While human-caused climate change is increasingly driving a 'new normal' marked by a warmer winter and shorter spring, scientists also draw attention to the yearly changes in weather patterns, termed 'year-to-year variability'.

"For example, updates from the IMD this year suggest that it was an unusually dry winter," Arpita Mondal, associate professor at the Centre for Climate Studies at IIT Bombay, told PTI.

She explained that rain is a natural cooling process that helps bring temperatures down.

Raghu Murtugudde, an earth system scientist and professor at IIT Bombay, said, "I see a global wave of warm and cold temperature anomalies (deviations from expected patterns) during Dec-Feb that are related to the swings of jet streams." Jet streams are strong winds blowing in the upper levels of the atmosphere and influence weather by shifting north and south.

Mondal said, "Our study finds that a northward shift in these winds during pre-monsoon is directly linked with heatwave character, such as its duration and temperature." Further, El Nino and La Nina -- phases of the 'ENSO' natural climate driver -- also contribute to the overall trends, Vimal Mishra, chair professor of civil engineering at IIT Gandhinagar, said.

"So, under El Nino-like conditions, you will see warm springs or hot temperatures just after winter, whereas if La Nina prevails, you will find more number of cool or cold days," Mishra said.

Much of the world's weather is significantly influenced by the 'El Nino-Southern Oscillation' (ENSO), involving changes in temperatures and atmospheric pressures in the Pacific Ocean.

An ENSO cycle oscillates between the 'El Nino' -- warm phase linked with warmer ocean temperatures -- and its counterpart 'La Nina', transitioning each time via a neutral phase. A cycle typically lasts between 2-7 years.

This week, the World Meteorological Organization (WMO) notified that the "weak" La Nina that emerged in December 2024 "is likely to be short-lived". The UN agency had predicted the La Nina a 60 per cent chance of emerging during July-September, following ENSO-neutral conditions that began in May 2024.

Further, temperatures during March 2024-February 2025 were 0.71 degrees Celsius above the 1990-2020 average, and 1.59 degrees Celsius above pre-industrial levels, Europe's Copernicus Climate Change Service said this week.

Sea surface temperatures remained unusually high in many ocean basins and seas, it said.

Murtugudde said, "It's not really a La Niña at all. It has some cold waters in the tropical Pacific (Ocean), but in the critical eastern Pacific, some warm anomalies have persisted. And this only emerged at the end of the year, as opposed to peaking during December-February." "The patterns are a bit unexpected, but likely related to the record warming of 2023 which is still continuing. We haven't really explained the level of warming yet," he added.

Studies have projected that in a warmer future, El Nino events are likely to become more common and intense, with every one in two of these being an extreme one.

The 2023-24 El Nino, one of the strongest five on record, is said to have fuelled rising temperatures and extreme weather events around the world in the period.

India experienced 536 heatwave days during summer 2024, the highest in 14 years, with the northwestern region seeing the warmest June since 1901, according to the IMD.

Mishra said, "The most robust, important signature is that of climate change. Therefore, even under ENSO-neutral conditions -- very much likely this year -- we cannot ignore harsh heatwaves, given that we have already started with quite warm temperatures in March." In its update this week, the WMO has predicted a 60 per cent chance of ENSO-neutral conditions during March-May 2025.

Further, under climate change, "an El Nino will cause a lot of problems for us, but La Nina may not be able to provide comfort to us," Mishra added.