A climatic connection that historically linked the Pacific and Indian Oceans has undergone a behavioral change in recent decades. A study published in the journal Nature Communications points out that global warming has modified the way atmospheric conditions in the Pacific impact Indian temperatures.
This transformation may have significant implications for long-term climate projections, given that Indian temperatures are crucial for determining rainfall patterns and other conditions in densely populated areas of Africa, Asia, and Australia.
The central mechanism involves the Walker circulation, a vast system of air movement over the tropical Pacific, driven by water temperature disparities. This system works by having air rise over warmer regions, circulate through the atmosphere, and descend in other locations, helping to define surface winds; during El Niño events, this circulation tends to weaken.
Traditionally, changes in the Pacific reached the Indian Ocean through an atmospheric bridge, following the Indian Ocean Basin Mode, which describes regional thermal behavior. However, this harmony has been lost.
Since the 1950s, the tropical Indian Ocean has registered a warming of approximately 0.1 °C per decade, correlated with the increase in greenhouse gas concentrations. Concurrently, the Pacific Walker circulation intensified starting in the 1980s.
To assess whether the current change is part of natural climate variation, Shawn Wang from the University of Colorado Boulder, and other researchers conducted a retrospective analysis spanning hundreds of years, combining modern data, climate models, and natural records. The reconstruction, covering the period from 1631 to 1990, revealed that in most of the four centuries examined, the patterns of the Pacific and Indian Oceans evolved together, with a notable exception occurring between 1810 and 1850.
During this specific interval, major tropical eruptions caused temporary disturbances in the climate system, including Mount Tambora in Indonesia in 1815. Eruptions of this magnitude release sulfurous gases that create aerosols in the atmosphere, decreasing the incidence of sunlight on the surface, which can lead to uneven cooling and alter oceanic temperatures and winds. Simulations indicate that this phenomenon weakened the link between the Pacific and Indian Oceans.
By comparing the observed relationship between 1945 and 2025 with simulated and reconstructed 80-year periods over the last century, researchers found that the current correlation is outside the 95% ranges established in historical records. A crucial conclusion is that global warming and human emissions are now overriding the natural influence of the Pacific on the Indian Ocean, according to Caroline Ummenhofer, a climate scientist at the Woods Hole Oceanographic Institution.
Although the break has not affected all climatic interconnections between the two oceans, a relationship involving the Indian Walker circulation did not show a similar significant alteration. Researchers also express uncertainty about the future of the Pacific Walker circulation, but warn that the detected change could complicate climate forecasts and lead to consequences for water resource management and risks.