Walker circulation

Definition

The Walker circulation was discovered and named for Gilbert Walker. The Walker circulation is a cell of airflow across an ocean along the Equator. The most well-known cell is across the Pacific Ocean, but cells also exist across the Indian and the Atlantic Oceans. In the western Pacific or Atlantic, hot air rises, carrying moisture and creating a wet climate. As the air travels eastward, it cools and creates a cooler, drier climate in the eastern Pacific. An ocean current follows the same pattern. The water warmed by the Sun flows to the west. The Indian Ocean Walker cell flows in the opposite direction, making the eastern side a warm, moist climate.

Significance for Climate Change

When a Walker circulation weakens or reverses, an El Niño results. The ocean surface temperature is higher than normal, and the normal upwelling of cold water is less, if at all. This means that plankton are not brought up to the surface, and anglers from Peru suffer from small catches of fish that eat plankton. A shift in the Walker cell has also been shown to cause drought and flooding in Australia. An El Niño year may cause the central or eastern region of the Pacific to be as warm as the western Pacific. The ocean around Australia is cooler with less moisture in the atmosphere, which causes a drier eastern and northern Australia. A stronger-than-normal Walker circulation, called La Niña, can cause severe flooding in Australia as the airflow carries more moisture, the ocean is warmer, and there is more rainfall. This also means more cyclones in Southeast Asia, droughts in South America, and colder winters in North America.

An El Niño year will have fewer hurricanes as strong western winds, normally blocked by the Walker circulation, form and disrupt hurricane formation. The drier western Pacific will include not only Australia but also Indonesia. The western Pacific region, such as Chile and Peru, will have greater rainfall. Canada will have colder temperatures, but Europe will have wetter, milder winters. A study by the University of Toronto indicates that a weaker Walker cell has such wide-ranging effects as less summer rainfall in West Africa and in north China and a reduced snow accumulation in the southern Himalayas. There is evidence that the Walker circulation weakened for most of the twentieth century. An article published in Nature Communications in 2024 indicated that the Walker circulation has slowed down or weakened because of global climate change. Experts predicted that it would most likely continue to weaken in the twenty-first century.

However, emerging research shows that while climate models project a long-term weakening of the Walker circulation under global climate change, observations since the late twentieth century reveal a temporary strengthening linked to persistent sea-surface temperature contrasts across the Pacific. Scientists expect this short-term strengthening to give way to renewed weakening later in the twenty-first century.

Müller-Dum, Denise. "Competing Effects of Global Warming and Sea Surface Temperature Explain Recent Strengthening of the Walker Circulation." Phys.org, 25 Feb. 2025, phys.org/news/2025-02-effects-global-sea-surface-temperature.html. Accessed 17 Aug. 2025.

“Study Explains Unexpected Recent Strengthening of the Walker Circulation.” Max-Planck-Gesellschaft, 25 Feb. 2025, www.mpg.de/24257079/study-explains-unexpected-recent-strengthening-of-the-walker-circulation. Accessed 17 Aug. 2025.

Toda, Masaki, et al. "Walker Circulation Strengthening Driven by Sea Surface Temperature Changes outside the Tropics." Nature Geoscience, vol. 17, 2024, pp. 858-865, doi.org/10.1038/s41561-024-01510-5. Accessed 17 Aug. 2025.

Wu, Mingna, et al. "Early Emergence and Determinants of Human-Induced Walker Circulation Weakening." Nature Communications, vol. 15, 2024, doi.org/10.1038/s41467-024-53509-6. Accessed 17 Aug. 2025.