Kevin Trenberth PhD on Ocean Heat Waves

January 8, 2020

Science Alert:

A swath of the Pacific Ocean larger than New South Wales is heating up, and fast.

About 800 kilometres (497 miles) east of New Zealand’s South Island, near the Chatham Islands, ocean temperatures have spiked to almost 6 degrees Celsius warmer than average.

Normally, surface temperatures in that part of the Pacific hover around 15 degrees Celsius (59 Fahrenheit), but the blobs is around 20 degrees Celsius (68 Fahrenheit), according to James Renwick, a scientist at Victoria University in Wellington, New Zealand.

“It’s the biggest patch of above-average warming on the planet right now,” Renwick told The Guardian.

In satellite images, this 1,000,000-square-kilometre (386,000 square mile) patch looks like a menacing red blob.

“Sea temperatures don’t actually vary too much, and a degree, plus or minus, is quite a big deal, and this area is probably 4 degrees [Celsius] or more than that above average and that’s pretty huge,” Renwick told The New Zealand Herald.

He added: “I don’t have an explanation for it.”

Since 1981, water temperatures off the New Zealand coast have increased by between 0.1 and 0.2 degrees Celsius on average per decade.

But when sea-surface temperatures spike precipitously, it’s considered a marine heat wave. These typically occur when weather causes the ocean to absorb more heat than usual or if certain conditions prevent the ocean from releasing heat.

In the case of New Zealand’s current hot spot, Renwick told The Guardian that the culprit could be an anti-cyclone that has settled above the region.

Anti-cyclones are high-pressure weather systems in which the atmosphere and surrounding air become heavy, stifling nearby winds and causing calm, stagnant conditions.

“It’s probably a very thin layer of ocean that has warmed up, and there hasn’t been any wind to cool it for several weeks,” Renwick said.

New Zealand experienced a comparable marine heat wave two summers ago, during which water temperatures spiked up to 3 degrees Celsius above normal.

Climate change can make these marine heat waves worse because the ocean absorbs 93 percent of the extra heat greenhouse gases trap on Earth. So as global warming gets worse, heat waves on land and in the ocean grow more intense.

“In a warming world, these events are going to become worse, and we are going to head toward a state where it is like a permanent marine heat wave,” Hillary Scannell, an oceanographer at the University of Washington, told The Washington Post in September.

In 2014, a marine heat wave plagued the Pacific Ocean between Hawaii, Alaska, and California. It led seal and sea-bird populations to die off, algal blooms to spread, and coral to bleach. Scientists nicknamed it ‘The Blob’.

Four years later, a similar heat wave bloomed in the same waters. That blob bleached coral in the Hawaiian Islands and stranded sea lions and whales on the California coast. Ocean temperatures were nearly 3 degrees Celsius warmer than average.

Those two blobs, much like New Zealand’s current hot spot, spell disaster for marine life. Warmer temperatures prompt coral to expel its algal food sources and turn ghostly white. This bleaching increases a coral’s risk of death and threatens the fish species a reef supports.

Other underwater ecosystems are also put at risk as waters warm. Higher sea temperatures make it difficult for bigger, more nutritious species of cold-water zooplankton – which feed fish and other predators – to thrive.

Fish and sharks abandon their traditional habitats in search of cooler waters; in 2018, a type of rare grouper fish from Queensland, Australia, was spotted almost 3,200 kilometres (2,000 miles) away in northern New Zealand.

In 2015, I examined the Northern Pacific heat “Blob” in this video.

2 Responses to “Kevin Trenberth PhD on Ocean Heat Waves”

  1. rhymeswithgoalie Says:

    Here’s the nullschool wind pattern for that area:
    https://earth.nullschool.net/#current/wind/surface/level/orthographic=173.48,-43.38,452

  2. jfon Says:

    New Zealand itself has been getting rather cool and wet weather lately. I thought it might be another example of a stuck Rossby wave – drought in Australia, with hot dry air from the north, could wet southerlies over NZ, then warm ocean to our east.


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