El Niño linked to accelerated ice loss in tropics

A phenomenon that typically occurs every two to seven years, El Niño causes much warmer than average ocean temperatures in the eastern Pacific, significantly affecting weather around the globe.

The Quelccaya Ice Cap (QIC) in the Peruvian Andes has been shown to be sensitive to these climate shifts, but the extent to which El Niño contributes to its continued shrinkage has, to date, been unclear.

Now, using images captured by NASA Landsat satellites over the past four decades, researchers have confirmed that the regional warming periodically caused by El Niño has indeed resulted in a drastic reduction of its snow-covered area. The study, led by Kara Lamantia, a graduate student at the Byrd Polar and Research Climate Center at The Ohio State University, found that between 1985 and 2022, the QIC lost about 58% of its snow cover and about 37% of its total area.

"Our research gives us a look into a glacier's health," said Lamantia. "The Quelccaya glacier becomes greatly out of equilibrium during these short-term climate anomalies."

The study, published today (October 8, 2024) in the journal The Cryosphere, is the first to automate the process of snow-covered area detection on the QIC. Normally, this detection is only possible through extensive field measurements or manually hand-tracing satellite images that are clear enough to detail the visual boundary between snow and ice.

Yet an algorithm this team developed processes images using near-infrared imagery, a method that utilizes wavelengths outside our visible spectrum. "By creating a threshold for the different reflectance between snow and ice cover, we can gather a consistent and much more reliable measurement," said Lamantia.

Glaciers and ice caps gain mass by accumulating ice and snow and lose it when none is received, or more ice is lost than gained. By measuring the ratio of snow-covered area to the total area, researchers can quantify whether the QIC is gaining mass, losing it, or maintaining a steady state.

The study revealed that during El Niños, the ratio drops significantly away from the average, indicating a drastic reduction in the snow-covered area.

This extreme change in its ratio may be attributed to the wide differences between the dry and wet seasons in southern Peru, said Lamantia.

"All of the snowfall happens during the wet season, but during an El Niño, southern Peru experiences warmer and drier conditions than average so it stays dry throughout the wet season," she said. "That means that the snow cover will continue to decline and there might be quite a bit less snowfall to replace it."

As climate change rapidly alters the Earth's environment, it's expected that El Niños are likely to be longer-lived and stronger, a factor that will accelerate ice loss. This raises the possibility of the QIC's snow cover failing to recover during La Niñas, or periods when the oceans should be cool.

"The ice cap as a whole is on a very consistent linear decline from anthropogenic warming," said Lamantia. "It may not matter how strong future La Niñas are, as the freezing line continues to rise and snow cover shrinks, Quelccaya will likely continue to decline."

If this carries on, some projections suggest that snow cover on the QIC could disappear by 2080, relegating it to a wasting ice field, much like Kilimanjaro. By the end of the century, the study notes, the ice cap could be no more.

It's difficult to discern how other short-term weather events might impact glacier vulnerability, which is something similar studies may aim to model in the future. What scientists do know is that ice loss puts high-mountain communities that depend on them in jeopardy, as snow loss can quickly diminish key water supplies.

The damage already done to the oceans and atmosphere is not something we can reverse tomorrow, Lamantia said. Using the data collected about their complex interactions, researchers may have a better chance at monitoring and mitigating the planet's climate woes.

"The general consensus is we can expect that the likely increased intensity and duration of El Niños will cause more complications for the QIC," said Lamantia. "We need to start being clever about how we use and conserve our water resources."

This study was supported by the National Science Foundation, the Heising-Simons Foundation and the Volo Foundation. Other co-authors were Lonnie Thompson and Bryan Mark from Ohio State and Laura J. Larocca of Arizona State University.