- As the latest U.N. climate change summit gets underway in Madrid, a paper published in Nature has drawn attention to the disruptive impact of warming oceans on the weather.
- It examines the effect of a swath of warm water in the Indo-Pacific Ocean, which has doubled in size since the turn of the 20th century, on the Madden-Julian Oscillation (MJO), a system of rain-bearing clouds, winds and pressure fronts that traverses eastward along the equator.
- The MJO affects the timing variability and strength of rainfall in many parts of the world, regulating among other things cyclone formation, the monsoon system, and the El Niño cycles.
- Changes in the amount of time the system lingers over a region, influenced by the expansion of the warm water pool in the Indo-Pacific, has caused disruptions in rainfall in Asia, Africa, Australia and the Americas.
An expanse of warm water in the Indo-Pacific doubled in size between 1900 and 2018, adding an area the size of California every year. The culprit? Rising carbon dioxide emissions, according to climate scientists, who write in a recent paper that the warm water system is already disrupting weather patterns across the world, from Asia to Africa and the Americas.
As the 25th Conference of Parties (COP) of the U.N. Framework Convention on Climate Change gets underway in Madrid, the paper published in Nature draws attention to the impact of warming oceans on global weather patterns. In particular, the study examines the effect of this expanding swath of warm water on the Madden-Julian Oscillation (MJO), a system of rain-bearing clouds, winds and pressure fronts that traverses eastward over the tropics along the equator.
The importance of the MJO can be gauged from the fact that it regulates, among other things, cyclone formation, the monsoon system, and El Niño cycles. The MJO contributes to severe weather events the world over, but has disparate effects in different places, playing a role both in the dry spell gripping California and the Arctic polar vortices that cause frosty winters in North America.
The authors of the Nature paper compared the size of the warm pool in the period 1900-1980 to its size in 1981-2018 and noticed the dramatic enlargement. They found that the swelling warm water pool skews the life cycle of the MJO. “Rapid warming over the tropical oceans during 1981-2018 has warped the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3-4 days, and increasing over the Indo-Pacific Maritime Continent by 5-6 days.”
The MJO usually originates over the Indian Ocean and travels eastwards over the Indo-Pacific Maritime Continent towards the Pacific Ocean, where it dissipates in the cooler waters of the eastern Pacific. The Indo-Pacific Maritime Continent refers to the area sandwiched between the Indian and Pacific Oceans spanning the archipelagos of Indonesia, Borneo, New Guinea, the Philippines and the Malay Peninsula.
The system is made of two poles of activity, one associated with more precipitation and the other with lower rainfall. It typically takes 30 to 60 days to pass from the Indian Ocean to the Pacific. Depending on how long it lingers over a region, its impact can be felt on weather patterns.
The longer lingering time identified by the authors led to increased rain in northern Australia, the western Pacific, the Amazon Basin, southwest Africa and Southeast Asia, while at the same time bringing drier conditions to the central Pacific, along the West and East coasts of the United States, north India, East Africa, and the Yangtze Basin in China.
“Climate model simulations indicate that continued warming of the Indo-Pacific Ocean is highly likely, which may further intensify these changes in global rainfall patterns in the future,” Roxy Mathew Koll, at the Indian Institute of Tropical Meteorology and first author of the study, said in a statement. “This means that we need to enhance our ocean observational arrays to monitor these changes accurately, and update our climate models to skillfully predict the challenges presented by a warming world.”
The research work was a collaboration between scientists at India’s Ministry of Earth Sciences, the U.S. National Oceanic and Atmospheric Administration (NOAA), the University of Washington, and the University of Tokyo.
Roxy, M. K., Dasgupta, P., McPhaden, M. J., Suematsu, T., Zhang, C., & Kim, D. (2019). Twofold expansion of the Indo-Pacific warm pool warps the MJO life cycle. Nature, 575(7784), 647-651. doi:10.1038/s41586-019-1764-4
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