Sea surface temp soars to highest in recorded history

New Delhi: Sea surface temperatures (SSTs) around the world are at their highest levels in recorded history this April. And extremely high SSTs over the Indian Ocean, particularly south Arabian Sea and Bay of Bengal currently, are contributing to record SSTs globally.

On April 5, the global average SST was 21.1 degree C , a new record according to data released by Climate Change Institute at University of Maine. It hasn’t cooled much since. On April 16 , it was 21 degree C, the same as the previous record set in March 2016.

The University’s Climate Reanalyzer which uses data from US’s National Oceanic and Atmospheric Administration (NOAA) shows SSTs over the tropics are high with the Indian Ocean region recording temperatures that are 29 to 31 degree C on April 16 (Sunday) nearing the top of the temperature spectrum on NOAA’s chart. The SSTs over the Indian Ocean are above normal by 1 to 2 degrees C according to climate scientists. If the SSTs remain exceptionally high, they can impact the monsoon in different ways, either by delaying onset or contributing to extreme rain events, they said.

Forecasts from Indian National Centre for Ocean Information Services (INCOIS) also show that the south Bay of Bengal and south Arabian Sea are expected to temperatures of a record 30-plus degrees C SST this week. There are also patches of strong marine heat waves over south Arabian Sea along Kerala and Karnataka and over Bay of Bengal along Bangladesh and West Bengal according to the Marine Heat Wave Tracker created by the Marine Heatwaves International Working Group. While the occurrence of marine heat waves may be a transient phenomenon, SSTs in excess of 30 degrees C are worrying, scientists said.

“SSTs over 30 degrees C are very high. You need around 27 degrees C to trigger convection over the ocean. Such warm temperatures definitely impacts marine life . This needs to be studied. The impact of high SSTs on themonsoon can be both positive and negative. For example, warm SSTs can contribute to development of low-pressure systems and genesis of depressions during monsoon. These systems bring rain. But very high ocean temperatures can also reduce the temperature gradient between land and ocean which is critical for onset of monsoon and rainfall activities. Onset can be delayed or slowed when this gradient reduces ” explained M Rajeevan, climate scientist and former secretary, ministry of earth sciences.

While ocean temperatures are shooting up mainly due to a rise in global average temperatures or climate change, the immediate cause is very high solar radiation combined with certain ocean dynamics, Rajeevan said. “The dynamics are similar for land and ocean but a little more complicated for ocean. High solar radiation warms land faster than the ocean. The Arabian Sea normally starts cooling off after the monsoon sets in.”

“Whenever there is an El Nino developing in the Pacific, that changes the winds and atmospheric circulation over the Indian Ocean, heating it up. Currently, we see that the Indian Ocean has started responding, with high sea surface temperatures across the basin. This is aggravated by the ocean warming trends in response to climate change,” said Roxy Mathew Koll, climate scientist working at the Centre for Climate Change Research at the Indian Institute of Tropical Meteorology (IITM).

El Nino is a phenomenon of warmer than expected ocean temperatures in the eastern equatorial Pacific, and has a correlation with a poor monsoon in India.

“Parts of the Arabian Sea, northern and southern Bay of Bengal, and the central equatorial Indian Ocean are exceptionally warm, with surface temperature anomalies over 1-2 degrees Celsius. There’s a marine heatwave warning in these regions, from NOAA. Marine heatwaves are exceptionally warm temperatures in the ocean that can lead to coral bleaching and fish mortality. As per global agencies and IMD, the El Nino conditions in the Pacific and the warming in the Indian Ocean is forecasted to continue into May-June. If the influence is strong, this may have a weakening effect on the monsoon winds and rainfall. At the same time, warm ocean temperatures in the Arabian Sea may result in extreme rains too. This is an ongoing trend in monsoon conditions as per our research, and we need a long-term policy to address the risks and water security issues that arise due to these impacts,” Koll added.

The global ocean has warmed continuously since 1970 and has taken up more than 90% of the excess heat in the climate system, the Intergovernmental Panel on Climate Change said in its Special Report on the Ocean and Cryosphere released in 2019. Since 1993, the rate of ocean warming has more than doubled and marine heatwaves have very likely doubled too in frequency since 1982 and are increasing in intensity. By absorbing more CO2, the ocean has undergone increasing surface acidification and loss of oxygen has occurred from the surface to 1000 m.