The frequency of extreme forms of a climate cycle that can cause devastating droughts and flood events from Indonesia to India to Kenya, may triple in the coming decades, according to a new study published Wednesday. The study, published in the journal Nature, ties manmade global warming to shifts in the behavior of a naturally-occurring climate cycle, known as the Indian Ocean Dipole (IOD).

Like the Pacific Ocean, which gives rise to El Niño and La Niña events, the Indian Ocean has its own inherent instability, with constant fluctuations between trade winds and sea surface temperatures across the ocean basin. These fluctuations, like oceanic and atmospheric mood swings, can interact in reinforcing feedback cycles, leading to positive or negative Dipole events that lead to huge changes in where it rains and how frequently and heavily it does so.

When these events are particularly extreme, they can have major repercussions for hundreds of millions across more than 1,000 miles, from Kenya to Australia northward into densely-populated India and Bangladesh.

The IOD was discovered in 1999, and since then, scientists have gained a better understanding of it through increased observations and computer modeling studies. The Dipole is now thought to be independent of El Niño, although the two cycles do interact with one another, and in some cases El Niño events can lead to a Dipole swing, the study's authors told Mashable.

The difference in sea surface temperatures between two areas, or poles, is what defines the phases of the IOD. The eastern pole is in the eastern Indian Ocean near Sumatra, with the western pole in the Arabian Sea. When the Indian Ocean Dipole is in a positive phase, there are warmer than usual sea surface temperatures in the western Indian Ocean and colder than average waters in the east, and trade winds blowing from west-to-east tend to lessen or even reverse direction entirely.

Negative IOD events bring the opposite conditions, with cooler than average ocean temperatures in the western Indian Ocean, and warmer waters in the east.

Extreme positive Dipole events, which are the main focus of the study, tend to lead to drought and wildfires in eastern Asia and Australia, floods in parts of the Indian subcontinent and eastern Africa, and coral reef bleaching events across western Sumatra. Coral reefs are sensitive to water temperature, and they can be damaged or even die off if temperatures get too high.

Diagram of positive and negative Indian Ocean Dipole events. Image: E. Paul Oberlander, Woods Hole Oceanographic Institution

During an extremely positive Dipole event in 1997, for example, there were major floods in Somalia, Ethiopia, Kenya, Sudan and Uganda. At the same time, there were drought conditions and wildfires in Indonesia, with smoke affecting tens of millions.

The study examines such extreme positive events, and finds that global warming is pushing the Indian Ocean toward a state that favors more of these occurrences, with waters that are warming faster in the west compared to the east, and anomalous winds from the east along and near the equator.

For the study, researchers in Australia and Japan used the newest generation of climate computer models to examine changes in specific indicators of extreme positive Indian Ocean Dipole events, including winds, ocean temperatures and rainfall variability. They found that the frequency of extreme positive IOD events will increase by a factor of 2.7, going from one every 17 years to one every six years, according to lead author Wenju Cai of the Commonwealth Scientific and Industrial Research Organization in Australia.

The study projects that there will be a decline of 25% in the number of moderate IOD events in the future at the same time that extreme events increase. The total number of moderate and extreme positive IOD events would increase from 525 events over 2300 years to 660 events over the same time period, Cai says.

The study is based on models using a high emissions scenario, assuming that countries choosing to follow a “business as usual” course on emissions, rather than significantly cutting greenhouse gas emissions to reduce the magnitude and rate of global warming.

The researchers only used computer models that are able to simulate extreme positive IOD events. “We are confident in our results because out of the 23 models that are able to produce extreme positive IOD, 21 models produce an increase,” Cai told Mashable in an email conversation. “The level of inter-model consensus is amazing. There is no way that this occurs by chance. More importantly, we demonstrate that the associated physical mechanism of the increased frequency is consistent with the mean state change.”

Co-author Agus Santoso, a researcher at the University of New South Wales in Sydney, Australia, told Mashable that a key factor that will make extreme positive IOD events more common is a weakening of an air circulation pattern in the tropics, known as the Walker Circulation. This weakening, which is projected to occur but has not yet been observed, would create background, or “mean state” conditions, in the Indian Ocean that would tilt the odds toward more frequent extreme positive IOD events, Santoso said.

Outside experts who were not involved with the new study questioned some of its findings, including the reliability of the model projections, but said it provides valuable insight into a relatively mysterious phenomena.

Peter Webster, a professor at Georgia Tech who has conducted research on the IOD as well as the South Asian Monsoon, told Mashable that the models used in the study have flaws in how they simulate the climate system to begin with.

“The next century projections need to be carefully assessed,” he said. “They are dependent on model projections and the models, even the very best have not simulated the "pause" or "hiatus" occurring since 1998. So one must worry a little that they are depending on models that have problems,” Webster said, referring to the slowdown in the rate of global warming since 1998.

Other outside researchers also said that “model bias” could be a problem with the study, although its conclusions may still be sound. “The results appears plausible and consistent with the the existing information about IOD and warming,” said P.N. Vinayachandran, a professor at the center for atmospheric and oceanic sciences at the Indian Institute of Science in Bangalore.

Santoso says the use of climate models helps to give scientists a glimpse into what the future may hold.

“We use models for these projections. These can be considered the best pool of climate models that the world currently has for understanding the issue,” he said in an email interview. “No models are perfect, but they are capable of simulating these events and are broadly consistent with our understanding of the climate system. As models get better and better, we will get a better estimate of the projection.”