A worrying climate change signal is emerging from the Indian Ocean, particularly over the Arabian Sea, where marine heatwaves (MHWs) are becoming increasingly frequent and intense, according to observations from the Indian National Centre for Ocean Information Services (INCOIS). Based on INCOIS observations between 2016 and July 2024, the Arabian Sea remained in the 'Watch' state of the INCOIS Marine Heatwave Advisory Services for close to 40 days every year. During these days, sea surface temperatures increased by about 0.5°C above normal, significantly more than in other areas of the Indian Ocean. This warming anomaly occurred along the shelf regions of India's western coastline.
Alert and Warning Stages
Further analysis revealed that marine heatwave conditions became intense for about 20 days every year, with sea surface temperatures rising about 1°C above normal levels, placing the area in the 'Alert' stage. Additionally, extremely high marine heatwaves with temperatures above 1°C above normal were observed for approximately five days per year in the Arabian Sea, classified under the 'Warning' category.
Causes of Increased Warming
The increased warming in the Arabian Sea is mainly due to enhanced heat absorption, decreased winter cooling, and the warming of global oceans caused by climate change. The semi-closed nature of the Arabian Sea also makes it easier for heat to get trapped. Experts at INCOIS noted that recent studies indicate weaker summer monsoonal circulation in parts of the Arabian Sea may be one factor escalating marine heatwaves.
Threats to Marine Life and Climate
The threats posed by rising marine heat include mass coral bleaching, deaths of marine life, biodiversity loss, impacts on fisheries, and rising sea levels. "The Arabian Sea has experienced a relatively increasing sea surface warming trend due to enhanced heat absorption, reduced winter cooling, and increasing background global warming. Reduced wind stress leads to weaker vertical mixing, shallow mixed layer ventilation, stronger upper-ocean stratification, and enhanced surface heat trapping. This creates favourable conditions for long-duration MHWs," said INCOIS director Balakrishnan Nair T M.
"Rising ocean temperatures are one of the major consequences of climate change. When sea surface temperatures increase, evaporation from the oceans also rises, adding more moisture to the atmosphere. This enhanced moisture contributes to the formation of low-pressure systems over the seas, which can eventually intensify thunderstorm activity and trigger extreme rainfall events over land areas. Higher marine activity also influences atmospheric circulation patterns, leading to an increase in land surface temperatures and changes in precipitation patterns," said Sivananda Pai, head of the regional meteorological centre of IMD in Chennai.
