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Scientists have raised concerns over Antarctica’s second biggest breeding ground for emperor penguins, where virtually nothing has hatched for the past three years.

Usually 15,000 to 24,000 breeding pairs of emperor penguins flock yearly to a breeding site at Halley Bay, considered a safe place that should stay cold this century despite global warming.

But almost none have been there since 2016, according to a study in Antarctic Science.

The breeding pair population has increased significantly at a nearby breeding ground, but the study’s author said it is nowhere near the amount missing at Halley Bay.

“We’ve never seen a breeding failure on a scale like this in 60 years,” said study author Phil Trathan, head of conservation biology at the British Antarctic Survey.

“It’s unusual to have a complete breeding failure in such a big colony.”

Normally about 8% of the world’s emperor penguin population breeds at Halley Bay, Mr Trathan said.

Black-and-white with yellow ears, emperor penguins are the largest penguin species, weighing up to 40 kilograms and living about 20 years.

Pairs breed in the harshest winter conditions with the male incubating their egg.

Scientists blame the sharp decline on climate and weather conditions that break apart the “fast ice” — sea ice that is connected to the land — where the emperor penguins stay to breed.

They incubate their eggs and tend to their chicks — one per pair — on ice. After breeding and tending to the chicks, the penguins move to open sea.

In 2016 and 2017, there was no breeding in Halley Bay and last year there was just a bit, the study found.

The nearby Dawson-Lambton breeding area, which had been home to a couple thousand pairs, increased to 11,117 pairs in 2017 and 14,612 pairs in 2018, the study said.

While that is encouraging, it does not make up for all that was lost at Halley Bay, Mr Trathan said. “Not everybody has gone to Dawson Lambton yet,” he said.

What is troubling is not that part of the colony has moved to Dawson-Lambton, it is that scientists thought of Halley Bay as a climate change refuge in one of the coldest areas of the continent “where in the future you expect to always have emperors,” Mr Trathan said.

David Ainley, a marine ecologist and penguin expert at the consulting firm HT Harvey & Associates, worried that some people will be more alarmed than they need to be because many of the penguins did not disappear, but just moved.

While not as scary as it may sound initially, with climate change “long term, it’s another question as alternate breeding sites likely will become harder to find,” said Mr Ainley, who was not part of the study.

The study makes sense, and sometimes dramatic environmental change can cause a breeding failure like this, said Stephanie Jenouvrier, a penguin expert at Woods Hole Oceanographic Institution who was not part of the study.

Mr Trathan said a super strong El Nino — a natural cyclical warming of the central Pacific that changes weather worldwide — melted sea ice more than usual and exposed the fast ice to wind and waves, making the breeding home less stable.

He said it is not possible to say yet if human-caused warming — from fossil fuel burning that creates heat-trapping gases globally — is a factor.

A 2014 study by Jenouvrier projected that because of climate change the global population of emperor penguins will likely fall by at least 19% by the year 2100.