A new study suggests that the climate connection between the tropical Indian and Pacific oceans can be disrupted by major volcanic eruptions, while human-caused greenhouse gas emissions may now be driving an even more unusual breakdown in that relationship. Researchers at the Woods Hole Oceanographic Institution (WHOI) combined paleoclimate evidence with climate model simulations to examine how closely the two ocean basins have behaved over the past several centuries. Their findings indicate that volcanism can temporarily weaken the climate link between the Indian and Pacific oceans.
More recently, however, human-driven climate forcing has produced what the researchers describe as an "exceptional" shift in the way climate variability in the two regions is connected. The study was published in Nature Communications under the title "Coupling of Pacific and Indian Ocean variability disrupted by 19th century volcanism." A Climate Connection That Usually Moves in Step Climate conditions across the Indian Ocean often respond to changes occurring in the Pacific Ocean. This connection helps shape broad patterns of rainfall, temperature, and atmospheric circulation across the tropics.
Since the 1980s, however, scientists have noticed that this relationship has weakened. The Indian Ocean has increasingly behaved differently from what would normally be expected based on conditions in the Pacific, a change that researchers have linked to climate warming. One challenge is that reliable instrumental climate records cover less than a century.
That makes it difficult to determine whether the recent change is truly unusual or simply part of a longer natural cycle. To look further back in time, the WHOI team turned to tropical paleoclimate records preserved in corals, tree rings, and stalagmites. These natural archives allowed the researchers to reconstruct Indian and Pacific Ocean climate conditions back to the early 1600s.
Volcanoes Disrupted the Ocean Link in the 1800s The paleoclimate evidence shows that the Indian and Pacific oceans remained closely connected through most of the past 400 years. Between 1810 and 1850, the relationship between the two ocean basins changed significantly. Researchers linked that disruption to a series of major tropical volcanic eruptions, which appear to have weakened the Pacific Ocean's usual influence over climate conditions in the Indian Ocean.
Computer simulations covering the past thousand years supported that interpretation. The strength of the disruption depended on both the size of the volcanic eruptions and the background climate conditions that existed at the time. "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," said co-author Caroline Ummenhofer, a senior scientist at WHOI.
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