HomeWorldResearch explains how climate change may affect the Indian Ocean Dipole

Research explains how climate change may affect the Indian Ocean Dipole

Scientists now have a much better understanding of how climate change can affect and cause seawater temperatures on one side of the Indian Ocean to be much warmer or colder than those on the other side, a phenomenon that can lead to sometimes deadly weather-related events. such as the great drought in East Africa and the great floods in Indonesia.

The analysis, described in a new study in Science Advances by an international team of scientists led by Brown University researchers, compares 10,000 years of past climate conditions reconstructed from various geologic record sets with simulations from an advanced climate model.

The findings show that around 18,000 to 15,000 years ago, as freshwater melted from a massive glacier that once covered much of North America poured into the North Atlantic, the ocean currents that kept the heat in the Atlantic weakened and set off a chain of events . in response. The weakening of the system eventually led to a strengthening of the atmospheric loop in the Indian Ocean, which keeps warmer water on one side and colder on the other.

This extreme weather pattern, known as a dipole, produces above average rainfall on one side (either east or west) and widespread drought on the other. The researchers saw examples of this pattern both in the historical data they studied and in the model simulation. They say the findings may help scientists not only better understand the mechanisms behind the east-west dipole in the Indian Ocean, but may one day help create more effective drought and flood forecasts in the region.

James Russell, study author and professor of earth, environmental and planetary sciences at Brown says “We know that patterns of precipitation and drought are important in today’s temperature gradients in the Indian Ocean, particularly in East Africa, but it has been challenging to show that these gradients change over long time scales and to link them to long-term patterns of precipitation and drought on either side of the Indian Ocean. We now have a mechanistic basis for understanding why some of the longer-term changes in rainfall patterns in the two regions have changed over time.”

The researchers characterize the dipole as an east-west dipole, where the water on the western side – which borders modern East African countries such as Kenya, Ethiopia and Somalia – is cooler than the water on the eastern side towards Indonesia. They saw that the warmer water conditions of the dipole brought more rainfall to Indonesia, while the cooler water brought much drier weather to East Africa.

This fits with what is often seen in recent dipole events in the Indian Ocean. For example, in October, heavy rain led to flooding and landslides on the Indonesian islands of Java and Sulawesi, killing four people and affecting over 30,000. At the opposite end, Ethiopia, Kenya and Somalia have experienced intense droughts since 2020 that threatened to cause famine.

The changes the authors observed 17,000 years ago were even more extreme, including the complete drying up of Lake Victoria – one of the largest lakes on Earth.

Brown for Environment and Society and Brown’s Department of Earth, Environmental and Planetary Sciences and lead author of the study says “The dipole essentially amplifies dry and wet conditions that could lead to extreme events, such as multi-year or decade-long dry events in East Africa and flooding in southern Indonesia, These are events that affect people’s lives and also agriculture in these regions. Understanding the dipole can help us better predict and prepare for future climate change.”

The dipole the researchers studied arose from interactions between a heat transport system in the Atlantic Ocean and an atmospheric loop, called the Walker circulation, in the tropical Indian Ocean. The lower part of the atmospheric loop flows from east to west over much of the region at low altitudes near the ocean surface, and the upper part flows from west to east at higher altitudes. The higher air and the lower air merge into one big loop.

The disruption and weakening of heat transport across the Atlantic Ocean, which acts as a conveyor belt of ocean and wind currents, was caused by the massive melting of the Laurentide Ice Sheet, which once covered most of Canada and the northern US. The melting cooled the Atlantic, and the resulting wind anomalies triggered the atmospheric loop over the tropical Indian Ocean to become more active and extreme. This then led to an increase in rainfall on the eastern side of the Indian Ocean (where Indonesia lies) and a decrease in rainfall on the western side where East Africa lies.

The researchers say more research is needed to determine exactly what effect the exposed continental shelf and lower sea levels have on the Indian Ocean’s east-west dipole, but they already plan to expand the work to investigate the question. While this line of work at lower sea levels will not play a role in modeling future conditions, the work they have done examining how the melting of ancient glaciers affects the Indian Ocean Dipole and the Atlantic Ocean heat transport system may provide key insights. to future changes as climate change brings more melting.

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