An important climatic link between the Pacific and Indian oceans has changed its behavior in recent decades, as shown by a study. Published in the journal Nature Communications, the work indicates that global warming has modified the influence of atmospheric conditions in the Pacific on temperatures in the Indian Ocean.
This change could have a significant impact on long-term climate predictions. Indian Ocean temperatures are crucial for determining rainfall patterns and other weather conditions in several populated areas of Africa, Asia and Australia, making predictability a greater challenge.
The ancient connection between the Pacific and Indian Ocean
The Walker Circulation, a vast air movement system located over the tropical Pacific and driven by variations in water temperature, plays a fundamental role in this climate mechanism.
When air rises over warmer regions, it circulates through the atmosphere and descends at other points, influencing winds near the surface. During the El Niño phenomenon, for example, this circulation can weaken.
Changes in the Pacific historically propagated to the Indian Ocean through a kind of atmospheric bridge. Previously, variations in the Walker Circulation were synchronized with the Indian Ocean Basin Mode, a pattern that describes the thermal behavior of the entire region.
However, this harmony was lost.
Since the 1950s, the tropical Indian Ocean has registered a warming of approximately 0.1°C per decade, coinciding with increasing greenhouse gas concentrations. In contrast, the Pacific Walker Circulation has intensified since the 1980s.
Historical analysis reveals the exceptionality of climate change
To see whether the current modification could be part of natural climate variability, Shawn Wang of the University of Colorado Boulder and his team of researchers investigated hundreds of years of climate history.
The group used a combination of recent observations, climate models and preserved natural records, covering the period from 1631 to 1990. The reconstruction was based on:
- 35 coral records;
- three tree ring records;
- a stalagmite log;
- climate simulations and observations.
For most of the four centuries analyzed, the Pacific and Indian patterns demonstrated synchrony. A notable exception occurred between approximately 1810 and 1850.
Large volcanic eruptions already affected the climate in the 19th century
In between, large tropical eruptions caused a temporary disruption in the climate system. Among these events, the eruption of Mount Tambora, in Indonesia, in 1815 stands out.
Eruptions of this magnitude release sulfur-containing gases, which form aerosols in the atmosphere and decrease the amount of sunlight reaching the surface. This uneven cooling can alter ocean temperatures and winds.
Simulations indicate that this cooling process weakened the connection between the Pacific and Indian Oceans at the time.
Global warming becomes the main current driver of change
The researchers compared the relationship observed between 1945 and 2025 with reconstructed and simulated 80-year periods over the last millennium. The current correlation fell outside the 95% ranges identified in historical records.
An important conclusion is that global warming and human emissions now outweigh the natural influence of the Pacific on the Indian Ocean, as Caroline Ummenhofer, a climate scientist at the Woods Hole Oceanographic Institution, stated in a note.
Despite the rupture, not all climatic connections between the two oceans were affected. A relationship involving the Indian Ocean Walker Circulation, for example, did not show a similar significant change.
Scientists also recognize that there are uncertainties regarding the future behavior of the Pacific Walker Circulation. Even so, the identified change could complicate climate predictions and have important consequences for risk and water resource management.