New study links rising sea surface temperatures to humid heatwaves over land

RIsing sea rise up temperatures in coastal ethel waters ar leading to a 50% to 64% increment in large-scale humid heatwaves o'er land, a new research paper published in Nature Geoscience on Tuesday has flagged.Warming Indian Ocean waters are closely linked to rising humid heat risks in South and West Asia, the paper by researchers at the Potsdam Institute for Climate Impact Research (PIK), Princeton University and Sun Yat-sen University, said.Similarly, warming of the tropical North Atlantic Ocean is increasing the risk of humid heat in northern South America. The study also shows that these ocean influences are stronger for large-scale events than for isolated local heatwaves.Humid heatwaves have intensified rapidly in recent decades and are projected to worsen, raising the risk of heat-related mortality, the Potsdam Institute for Climate Impact Research said in a note.Also Read: Enhance ocean observations to forecast extreme weather: Parliamentary committeePrevious research has indicated that even healthy people can succumb to wet-bulb temperatures—a measure combining heat and humidity—above 31.5°C, when the body is no longer able to cool itself by sweating. HT had reported on April 17 that the widely accepted wet-bulb temperature survival threshold of 35°C is being questioned after recent physiological studies suggest the limit may actually be closer to 31°C, Harvard researchers revealed following a recent interdisciplinary conference with the Union environment ministry to discuss heat stress in India and adaptation interventions.However, the widespread occurrence of humid heatwaves across large regions, like the 2023 heatwave in Asia, has so far remained poorly understood.The authors used a complex network approach applied to climate reanalysis data to show that the observed intensification of humid heatwaves is closely associated with coastal oceanic warming over the period 1982–2023.“This linkage is more pronounced for the large-scale aggregation of extreme humid heatwaves than for locally confined events. In particular, approximately 50% and 64% of the upward trends in humid heatwave frequency and spatial aggregation strength over hotspot regions are linked to their adjacent oceans, respectively,” the paper states.These land–ocean linkages largely arise from tropical ocean-driven moisture transport towards land regions. Ocean–atmosphere coupling modes, such as El Niño and the Indian Ocean Dipole, have been found to aggravate humid heat risks by triggering atmospheric Rossby wave trains. Rossby waves are huge, undulating movements of the atmosphere that stretch horizontally across the planet for hundreds of kilometres in a westward direction. They are so large and massive that they can change Earth’s climate conditions, according to the National Oceanic and Atmospheric Administration.Compared with mid-to-high latitudes, the tropics encompass most high-risk areas and exhibit stronger land–ocean linkages, highlighting the critical role of tropical oceans, the authors have said.“We see a strong link between warming coastal waters and clustered hot, humid extreme events, especially in the tropics, where oceans supply more moisture to the atmosphere, which is then transported to land, amplifying the heat,” said lead author and PIK scientist Fenying Cai in a statement. “In regions further from the equator, combined land-ocean warming, linked to large-scale atmospheric wave patterns, also plays an important role,” he added.Significant warming in the tropical Indian Ocean coincides with regional humid heatwaves over both South and Western Asia, the network analysis revealed.“Enhanced evaporation from warmer oceans typically leads to higher atmospheric humidity. Simultaneously, warming in the Indian Ocean induces a low-level cyclonic circulation anomaly over the Arabian Sea, enhancing moisture convergence and intensifying humid heatwaves in adjacent regions, including South and Western Asia,” the paper states.“Better understanding these land-ocean interactions can help to improve climate adaptation strategies. Crucially, coastal sea surface temperatures emerge as a potential early warning indicator for widespread humid heat extremes,” said co-author and PIK scientist Jürgen Kurths.HT reported on March 19 last year that the Indian Ocean has been warming rapidly over the past few decades, with a sea surface temperature estimate recording a 0.15°C increase per decade between 1951 and 2015, the Ministry of Earth Sciences (MoES) said in the Lok Sabha.HT reported on April 28, 2024, that the Indian Ocean basin, the fastest-warming basin in the world, will see accelerated warming at a rate of 1.7°C–3.8°C per century during 2020–2100, a new research paper has projected, warning that this will lead to an increase in severe weather events, prolonged marine heatwaves and extreme Indian Ocean Dipole events that will influence the monsoon and cyclone development.The authors used observed data for the historical period and the Intergovernmental Panel on Climate Change’s climate simulations under low-to-high emission scenarios to simulate future conditions in the Indian Ocean. Based on the current trajectory of emissions, the ocean will be somewhere between these two scenarios, said Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology, who led the research.