Researchers say they now have a significantly deeper understanding as to how climate change can affect and end up causing seawater temperatures on one side of the Indian Ocean to be much either warmer or cooler than temperatures on the other, a phenomenon that can lead sometimes to deadly weather-related happenings like megadroughts in East Africa and severe flooding in Indonesia, thanks to a new analysis of long-term climate data.
How climate change impacts the Indian Ocean dipole
CHAIDEER MAHYUDDIN/AFP via Getty Images
An international team of scientists led by Brown University academics compares 10,000 years of previous climatic conditions reconstructed from diverse sets of geological data to simulations from an advanced climate model in a new study published in Science Advances, as per ScienceDaily.
According to the results, some 18,000 to 15,000 years ago, as melting waters from the huge glacier that formerly covered most of North America poured into the North Atlantic, ocean currents that kept the Atlantic Ocean warm diminished, triggering a cascade of events.
The system's weakening eventually led to the development of an atmospheric loop in the Indian Ocean that traps warmer water on one side and colder water on the other.
This unusual weather pattern, known as a dipole, causes higher-than-average rainfall on one side (either east or west) and widespread drought on the other.
This pattern was evident in both the historical data and the model's simulation, according to the researchers.
They claim that the discoveries will assist scientists not only in better understanding the mechanisms underlying the east-west dipole in the Indian Ocean but will also one day aid in the production of more accurate drought and flood forecasts in the region.
The researchers describe the principles behind how the Indian Ocean dipole they researched evolved and the weather-related events it caused throughout the period they analyzed, which spanned the end of the last Ice Age and the beginning of the present geological epoch, in their study.
The dipole is described by the researchers as an east-west dipole, with water on the western side colder than water on the eastern side, which borders modern-day East African nations such as Kenya, Ethiopia, and Somalia.
They discovered that the dipole's warmer water temperatures sent more rain to Indonesia, while the colder water produced considerably drier weather in East Africa.
This is consistent with recent Indian Ocean dipole episodes. Heavy rain, for example, caused floods and landslides on the Indonesian islands of Java and Sulawesi in October, killing four people and affecting over 30,000 people.
On the other hand, Ethiopia, Kenya, and Somalia faced severe droughts that threatened famine beginning in 2020.
Scientists witnessed even more drastic changes 17,000 years ago, including the entire drying of Lake Victoria, one of the world's biggest lakes.
The dipole investigated by the researchers was generated by interactions between the Atlantic Ocean's heat transport system and a tropical Indian Ocean atmospheric loop known as the Walker Circulation.
At low altitudes near the ocean surface, the lower component of the atmospheric loop flows east to west throughout much of the region, while the top part flows west to east at higher altitudes. The upper and lower air combine to form a large loop.
The huge melting of the Laurentide ice sheet, which originally covered much of Canada and the northern United States, caused an interruption and weakening of the Atlantic Ocean heat transfer, which functions like a conveyor belt formed of ocean and wind currents.
As the Atlantic cooled, wind anomalies caused the atmospheric loop over the tropical Indian Ocean to become increasingly active and intense.
This resulted in more precipitation on the east side of the Indian Ocean (where Indonesia is located) and less precipitation on the west side, where East Africa is located.
The researchers further show that this effect was exacerbated throughout the study period by decreased sea levels and exposure to adjoining continental shelves.
Changes in sea surface temperature can have a variety of effects on marine ecosystems, as per EPA.
Variations in ocean temperature, for example, can affect which species of plants, animals, and microbes are present in a given location, alter migration and breeding patterns, endanger sensitive ocean life such as corals, and change the frequency and intensity of harmful algal blooms such as "red tide."
In the long run, increases in sea surface temperature may also reduce circulation patterns that bring nutrients from the deep sea to surface waters.
Changes in reef habitat and nutrient availability might drastically alter ocean ecosystems and lead to fish population decreases, affecting those who rely on fishing for food or a living.
Because the seas are constantly interacting with the atmosphere, sea surface temperature may have a significant impact on the global climate.
The amount of atmospheric water vapor over the seas has increased as sea surface temperature has risen.
This water vapor feeds weather systems, increasing the likelihood of heavy rain and snow. Changes in sea surface temperature can cause storm tracks to alter, perhaps causing droughts in some places.
Increases in sea surface temperature are also projected to increase the growing season for some bacteria that may taint seafood and cause foodborne diseases, raising the likelihood of adverse health impacts.
