Study finds human-caused warming intensifies El Niño

A study of Pacific Ocean surface temperatures has found a link between global warming and stronger El Niño events, ERR reported, citing Nature. Coral skeletons collected from the Galápagos Islands show that extreme climate events have become significantly more frequent since the Industrial Revolution.

El Niño is the warm phase of the El Niño Southern Oscillation, a natural temperature fluctuation in the tropical Pacific. It temporarily raises the planet’s average temperature and alters weather patterns worldwide. Warmer surface waters affect the distribution of winds and rainfall, potentially causing severe drought in some regions and heavy rainfall in others.

The El Niño that began in June could become one of the strongest on record, according to forecasts. It is already the third very strong El Niño in the past 11 years, which scientists consider unusual. The pattern has renewed debate over whether human-caused climate change is making El Niño events more frequent and more intense.

Until now, gaps in the underlying data have made firm conclusions difficult. Reliable temperature records from remote parts of the tropical Pacific largely extend back only to the 20th century. Computer models cannot fully reproduce the complex interactions between winds and ocean water that drive the ENSO cycle, making it difficult to assess natural ENSO variability before human-caused warming began.

Corals preserve climate history

Paleoclimatologists use natural archives, including tree rings and marine fossils, to study past climates. Corals provide particularly valuable information because their growth records changes in the ocean month by month. That level of detail is needed to identify the effects of short-term events such as El Niño.

Coral polyps build their limestone skeletons from calcium carbonate extracted from seawater. Like tree rings, growth layers form in coral skeletons, and their chemical composition depends partly on the temperature of the surrounding water. By analysing different layers in cores taken from coral colonies, scientists can estimate past ocean temperatures.

Earlier coral data from the central Pacific had already shown that strong El Niño events have become more common in recent decades. However, data from the eastern Pacific were missing, even though El Niño’s effects are strongest there.

Although the Galápagos Islands are located in the region, relatively few corals grow there. A few years ago, lead study author Julia Cole received information about corals found in a remote part of the archipelago. Her research team subsequently collected thousands of samples and reconstructed a 1,000-year record of changes in the region.

The dataset, described in the journal Science, shows that the range of ENSO fluctuations in the eastern Pacific has increased over the past millennium. The change has been particularly pronounced over the past century, when human-caused warming also accelerated.