In 2019, two weather extreme events were linked to higher-than-usual temperature differences between the two sides of the Indian Ocean: torrential rain in East Africa and exceptionally dry conditions fuelling bushfires in Australia. Several meteorologists refer to this climatic phenomenon as the Indian Ocean Dipole.
The Indian Ocean Dipole has played a huge role in both of these weather disasters. Flooding and landslides in East Africa have killed people and forced hundreds of thousands from their homes. Meanwhile, the bushfire season last year in Australia has been one of the most devastating on record. Sydney, the country’s most populous city, was choked under a blanket of thick smoke while its air quality exceeded hazardous levels on several occasions.
What is the Indian Ocean Dipole?
The IOD has only been recognized for about 20 years, thus, it is less studied compared to other climate patterns. Often called the "Indian Niño" because of its similarity to its Pacific equivalent, this phenomenon refers to the difference in sea-surface temperatures in opposite parts of the Indian Ocean. In scientific terms, the IOD is a coupled ocean and atmosphere phenomenon. The changes in temperature gradients across the Indian Ocean result in changes in the preferred regions of rising and descending moisture and air.
According to BBC, an operational business division of the British Broadcasting Corporation responsible for the gathering and broadcasting of news and current affairs, the IOD cycles through phases referred to as "positive,” "neutral,” and "negative” as temperatures in the eastern part of the ocean oscillate between warm and cold compared with the western part. A positive IOD would mean warmer sea surface temperatures in the western Indian Ocean relative to the east; negative means cooler sea surface temperatures in the western Indian Ocean relative to the east, while a neutral phase would mean sea temperatures were close to average across the Indian Ocean.
The dipole's positive phase last year resulted in higher-than-average rainfall and floods in eastern Africa and droughts in southeast Asua and Australia. "When an Indian Ocean dipole event occurs, the rainfall tends to move with the warm waters, so you get more rainfall than normal over the East African countries. On the other hand, in the east of the Indian Ocean, sea surface temperatures will be colder than normal and that place will get a reduced amount of rainfall,” Dr. Andrew Turner, a lecturer in monsoon systems in the UK's University of Reading, said.
Normally, a positive IOD would die off at the end of November or start of December as the monsoon moves into the southern hemisphere. Unfortunately, scientists say that it is taking more time than usual. “It's pretty sluggish moving into the southern hemisphere and hence we're waiting to see it move a little further before we become more confident of when the IOD may end,” they said.
IOD Events Are Becoming Stronger and More Frequent
The positive phase of IOD last year was the strongest the world had since 1997, according to scientists. Thus, it’s not surprising that the phenomenon played a huge role in Australia recording its driest spring on record and the fifth-warmest. Andrew Watkins, the Bureau of Meteorology's head of long-range forecasting, said that it also contributed to Perth posting its hottest ever start to summer. Meanwhile, the Famine Early Warning Systems Network reported that rainfall across the greater Horn of Africa was up to 300% above average from October to mid-November last year.
Unfortunately, these weather events linked with IOD will only get stronger and more frequent. A 2019 study revealed that global heating is “supercharging” the phenomenon. Scientists and humanitarian officials said that IOD threatens to reappear more regularly and in a more extreme form as sea surface temperatures rise. According to Guardian, a British daily newspaper, Caroline Ummenhofer, a scientist at Woods Hole Oceanographic Institution in Massachusetts, said that research suggests that IOD events have become more common with the warming in the last 50 years.
“The Indian Ocean is particularly sensitive to a warming world. It is the canary in the coalmine seeing big changes before others come to other tropical ocean areas,” Ummenhofer said.
Gemma Connell from the UN’s Office for the Coordination of Humanitarian Affairs expressed her concern about the impacts of stronger and more regular IOD events on Africa. One of the impacts is large-scale flooding across the region, which affects over 2.5 million people. “And putting it in the broader picture of the climate crisis, this flooding is coming on the back of two droughts. What we are seeing, and what we are going to see more of, is more frequent climatic shocks coming. And all that is on top of the violence and conflict that has already displaced many of the people involved,” Connell said.
Indian Ocean El Niño is Emerging
El Niño, which triggers disruptions of temperature, winds, and precipitation, is the recurring climate phenomenon across the tropical Pacific. Recently, scientists from the University of Texas at Austin found out that a new one in the Indian Ocean could have devastating consequences. Research suggests that climate change could trigger an ancient El Niño-like pattern in the Indian Ocean, creating extreme weather such as floods, storms, and droughts across the globe.
According to Phys.org, an internet news portal that provides the latest news on science, the researchers analyzed climate simulations and grouped them according to how well they matched present-day observations to show whether an Indian Ocean El Niño can occur in a warming world. The results of the simulations revealed that the phenomenon could emerge by 2100, but if warming trends continue it could occur as early as 2050.
The findings published in the journal Science Advances showed that global warming could disturb the Indian Ocean's surface temperatures. This could cause temperatures to rise and fall year to year much more steeply than they do today. This pattern is similar to El Niño, a climate phenomenon that occurs in the Pacific Ocean and affects weather globally.
"Our research shows that raising or lowering the average global temperature just a few degrees triggers the Indian Ocean to operate exactly the same as the other tropical oceans, with less uniform surface temperatures across the equator, more variable climate, and with its own El Niño," lead author Pedro DiNezio, a climate scientist at the University of Texas Institute for Geophysics, said.