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How a hot blob off New Zealand is contributing to drought in South America | Environment

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A vast patch of warming water off the coast of New Zealand – referred to as a “warming blob” – has contributed to a decade long drought affecting parts of South America, according to scientists.

Researchers based in New Zealand and Chile have examined the rapidly warming hot blob which rose to prominence in 2019 after spikes in water temperature of up to 6C were recorded.

In the new study, published in the Journal of Climate, the scientists used computer simulations to investigate whether there was a link between the blob, which spans an area about the size of Australia, and years of low winter rainfall in Chile.

Their models found the blob produced a dry ridge of high pressure across the south Pacific that blocked storms from reaching central Chile and pushed them towards west Antarctica.

“This big ridge of high pressure blocks storm systems that bring rainfall to central Chile in winter,” Kyle Clem, one of the authors and a lecturer in climate science at Victoria University of Wellington, said.

“When we took the blob out of our simulations that ridge of high pressure disappears.

“That was one our biggest pieces of evidence that the blob is a major contributor [to the drought].”

The ongoing drought has reduced fresh water supplies in Chile and prompted the science minister, Andres Couve, to say this month the decline of water reserves due to climate change was a national priority.

Clem said the researchers ran models that examined a 40 year period from 1979 through to 2018.

He said the simulations found that natural variability and reduced rainfall in the tropical central Pacific allowed a blob to form, even without the influence of human-caused global heating.

But he said the models showed the rate of warming of the patch of ocean was much higher because of greenhouse gases that occurred as a result of human activity and the burning of fossil fuels.

They found the blob had warmed 1.5C over the 40 year period, about three times the global average increase in sea surface temperature.

“The remarkable rate of warming in the blob contributes to a stronger ridge of high pressure across the southern Pacific,” Clem said.

“So what’s worrying – and this is the next area of research that we’re going to go down – is we need to understand the physical mechanisms that are maintaining the blob for such a long period of time.”

James Renwick is the head of geography, environment and earth sciences at Victoria University in Wellington. He was not an author on the paper but has studied the blob in the past.

He said the patch of warm ocean had been present for a long time but had not been the subject of much research and the new paper gave it some context.

“You can compare it to what happens in Australia with El Niño,” he said.

“It’s not quite equivalent but it’s the same story. You get a buildup of energy somewhere and that energy has to be dealt with.

“The net result is there’s this quite marked drying in parts of Chile.”

He said the rate of warming of that area of ocean showed what occurred when natural variation was combined with human-caused global heating.

“That’s the story of climate change,” he said.

“It’s quite amazing how much heat is being pumped into that ocean in that area east of New Zealand.”

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The Groucho

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