A new Woods Hole Oceanographic Institution study reveals that human-caused greenhouse gas emissions and global warming are driving an unprecedented breakdown in inter-basin coupling of the tropical Indian and Pacific oceans. Published in Nature Communications, the findings show that while 19th-century volcanic eruptions temporarily disrupted ocean connections, modern anthropogenic forces are overwhelming the Pacific’s natural influence.
Unprecedented Breakdown Driven by Human Emissions
For centuries, climate conditions in the tropical Indian Ocean have typically followed the behavior of the Pacific Ocean. That long-standing atmospheric and oceanic relationship, however, has broken down in the decades since the 1980s according to researchers at the Woods Hole Oceanographic Institution.
While previous scientific research often examined individual ocean basins in isolation, this investigation focuses directly on how the world’s oceans influence one another. Climate connections between these massive basins give scientists critical tools to predict future shifts in rainfall patterns and other aspects of the climate.
“A key finding is that global warming and human emissions are now overwhelming the Pacific’s natural influence on the Indian Ocean.”
Caroline Ummenhofer, Senior Scientist at WHOI
The study highlights the massive scale of the Indian Ocean as a heat reservoir. Because of that immense heat capacity, researchers observed that the basin possesses the capability to decouple from Pacific dynamics as detailed in published findings.
“The Indian Ocean is a huge heat reservoir, and it can decouple from what the Pacific Ocean is doing. The results of this study underscore the independent behavior of the Indian Ocean.”
Delia Oppo, Emeritus Research Scholar at WHOI
Using Paleoclimate Archives to Contextuzo-Temporal Shifts
Assessing the true rarity of modern climate shifts presents a distinct challenge because quality instrumental data spans less than a hundred years. To establish a much broader historical baseline, WHOI researchers turned to tropical paleoclimate archives—specifically analyzing corals, tree rings, and stalagmites to extend the climate record back to the early 1600s.
These paleo-records confirm that the Indian and Pacific ocean basins remained largely coupled for most of the last four hundred years. Yet the data also uncovers a striking historical anomaly during the early 19th century, specifically between 1810 and 1850, when the inter-basin relationship looked notably different.
Computer simulations covering the past millennium support the conclusion that a series of large tropical volcanic eruptions caused that 19th-century disruption. The extent to which past volcanism weakened Pacific influences depended on the strength of the eruptions and prevailing climate conditions at the time.
Contrasting Volcanic Disruptions With Modern Anthropogenic Forcing
A central contribution of the new research is demonstrating how past volcanic events compare against modern greenhouse gas emissions. While volcanic forcing caused temporary disruptions centuries ago, current human-driven climate pressures are creating an exceptional and sustained break in inter-basin coupling documented in the Nature Communications study, titled Coupling of Pacific and Indian Ocean variability disrupted by 19th century volcanism.
Photo: Woods Hole Oceanographic Institution
“This is one of the first studies to examine the breakdown in the connection between the Pacific and Indian oceans using evidence from past climates, modern observations, and climate models.”
By combining computer simulations, modern observations, and centuries of paleo-data, researchers can evaluate recent environmental changes with far greater confidence as explained by study authors.
“The modern data we have is limited and doesn’t go back far enough. With climate models and paleo-records, we are now able to say with more confidence that the recent changes we are seeing are really quite exceptional.”
Shawn Wang, former WHOI graduate student and postdoctoral researcher, current postdoc at the University of Colorado Boulder
The study was supported by the U.S. National Science Foundation, the WHOI Investment in Science Program, and the WHOI Academic Programs Office.
