A warning made more than a decade ago that rising seas could submerge large parts of Kochi is gaining fresh significance as new research suggests that ocean warming could be a major driver of sea-level rise along Kerala’s coast. 

Scientists at the National Institute of Oceanography (NIO) had earlier used satellite imagery and a digital elevation model to map possible inundation in Kochi, warning that rising sea levels could severely affect the city’s population, coastal environment, fishing, agriculture and other economic activities.

The study by NIO scientists had also pointed to the rapid expansion of Kochi and the growing environmental pressure on the city.

More recent research suggests that the process driving part of that future risk is already under way in the waters off Kerala.

A study of sea-level changes in the North Indian Ocean between 2003 and 2024 has found that ocean warming is a primary driver of sea-level rise in the region. For Kerala, which lies along the Eastern Arabian Sea (EAS), the finding is particularly significant.

The study, Sub-basin sea level budget analysis in the North Indian Ocean (2003–2024), found that thermal expansion accounts for the largest share of the change in sea level caused by changes in seawater density in the Eastern Arabian Sea.

In simple terms, warmer seawater expands. So the sea can rise even without additional water entering it from melting ice.

The estimated total sea-level rise in the Eastern Arabian Sea is 4.80 ± 0.28 mm a year, with ocean warming playing a major role alongside the addition of water to the sea.

The recent findings come at a time when the world's oceans are experiencing an extraordinary spell of heat.

Global sea surface temperatures remained above the previous record for the corresponding dates for 100 consecutive days between June 2 and September 10, according to the US-based Climate Reanalyzer.

Data from the European Union's Copernicus Climate Change Service, which has maintained global daily records since 1979, showed that ocean temperatures reached an all-time high of 21.10°C on August 22, 2026. The figure narrowly surpassed the previous record of 21.09°C recorded in March 2024.

Scientists attribute the long-term warming primarily to climate change, while El Niño is adding further heat to the oceans. The current El Niño is expected to strengthen until the end of December, and scientists forecast the likelihood of Pacific Ocean temperatures rising more than 2°C above normal, which is popularly described as a 'Super El Niño'.

Such conditions could add further pressure to already warming seas.

Kerala's monsoon and fisheries at risk

For Kerala, the concern goes far beyond the possibility of more intense summer.

The state has a 590-km coastline, and changes in the Arabian Sea can influence both its weather and marine ecosystems. Kerala is also already dealing with a monsoon deficit this year.

Biju Kumar, vice-chancellor of Kerala University of Fisheries and Ocean Studies, told Mathrubhumi English that rising sea-surface temperatures could be contributing to changes in Kerala's rainfall pattern.

"Warmer seawater increases evaporation, while winds transport the additional moisture and influence where condensation and rainfall occur. Changes in these processes can alter the state's rainfall pattern," he said.

The impact of rising temperatures, however, is not limited to rainfall. Kumar said the marine ecosystem itself is also under stress.

"Higher temperatures can reduce oxygen levels in seawater and create conditions favourable for the growth of toxic algae. Fish that consume such algae can become a food-safety concern. Kerala has previously reported deaths attributed to the consumption of fish that had fed on toxic algae," he said.

Rising temperatures could also have implications for the fisheries sector, particularly breeding.

"Many commercially important species along the Kerala coast, including sardines and mackerel, are concentrated in the upper layers of the sea. Changes in surface-water temperature can therefore affect their habitat and productivity," Kumar said.

He also pointed to the importance of the monsoon season for marine species.

"The monsoon is an important breeding period for marine species. If warmer waters disrupt breeding, the effects may be felt in the following fishing season through changes in the number of young fish entering the population," he said.

Ocean warming can also accelerate the deterioration of seafood by encouraging bacterial and fungal contamination.

Kumar said the consequences of a warmer sea are not restricted to fish, with people working at sea and along the coast also facing greater heat exposure.

"People working on fishing boats and along the coast are directly exposed to rising heat. Longer exposure can increase the risk of fatigue and sunburn, while high temperatures can make already difficult working conditions more dangerous," he said.

He also suggested measures to protect fishing communities from heat exposure.

"In West Bengal coast, there is a practice of mounting shades or covers on boats. Similar heat-protection measures could be considered in Kerala as well with government’s intervention. Ensuring access to drinking water for fishing communities going to sea to keep them hydrated should be considered," he added.

The consequences of a warmer Arabian Sea are not confined to fisheries or people working along the coast. Changes in ocean conditions can also affect coastal habitats that act as natural buffers against environmental pressures.

Grinson George, director of the Central Marine Fisheries Research Institute (CMFRI), told Mathtubhumi English that rising temperatures pose a threat to coral reefs.

"El Niño events have triggered coral bleaching in previous years, ranging from mild to severe, and repeated bleaching has affected reef diversity," he said.

George also said mangroves could come under pressure as atmospheric and oceanic conditions change.

"Changes in ocean temperatures alter atmospheric and oceanic conditions, influencing the behavior of cyclones. The rising sea surface temperatures generates thermal stratification, which has been linked to an increase in the intensity and rapid intensification of severe cyclones. While these storms act as a natural mechanism to redistribute heat across the globe, their rising destructive power threatens coastal biology. Mangroves act as a crucial natural buffering mechanism against cyclones by stabilizing shorelines and reducing storm surge impacts. However, the destructive power of these storms is amplified due to human-induced global warming, which fuels stronger winds. Consequently, strong cyclones can heavily damage mangroves and other coastal habitats, stripping away the vital ecosystems that provide natural protection to the shoreline," he explained.

A slow-moving threat

The recent sea-level study also points to a less visible factor behind the warming Arabian Sea.

A weakening of the Indian summer monsoon circulation over several decades has reduced southward heat transport and suppressed normal upwelling. With less cooler water reaching the surface, more heat can remain trapped in the upper layers of the Arabian Sea.

The Eastern Arabian Sea is also different from the western part of the basin in another important respect. The recent study found no statistically significant salinity-driven trend that would offset the effect of thermal expansion.

Year-to-year sea-level changes in the Eastern Arabian Sea also show a weaker relationship with major climate patterns such as the Indian Ocean Dipole and El Niño–Southern Oscillation than those in the Bay of Bengal.

The prospect of a stronger El Niño later this year adds another layer to the evolving conditions, even as its effects on the region remain subject to natural variability. From sea-level changes and monsoon patterns to fisheries, coral reefs and mangroves, the developments underline the need to closely track how warming waters are changing Kerala’s coastal and marine systems.