Ocean temperature surge signals climate shift
June 10, 2023
THE WASHINGTON POST – A rapid surge in global ocean temperatures in recent months is raising the specter of a climate pattern shift that could accelerate planetary warming and supercharge trends that already are fuelling extreme storms, deadly heat waves, and ecological crises on land and sea.
On the heels of a new annual heat record set in 2022 – the latest in a string of record-setting years – average ocean surface temperatures around the globe have spiked since early March. Excluding polar regions, they are about two-tenths of a degree Celsius warmer than scientists have ever observed at this time of year via satellite data.
Translation: What might seem like a small uptick in temperature can have profound effects.
“Averaged over the planet, that’s a really big anomaly,” saidresearch scientist at the Climate Change Research Centre at the University of New South Wales in Australia Alex Sen Gupta.
A transition to the climate pattern known as El Niño is probably behind the warming trend, scientists said. They won’t be sure of that until more time passes and the pattern takes shape. What’s already certain: as greenhouse gas emissions drive a steady surge in global temperatures, the planet will continue to set new climate and weather precedents, and oceans will grow ever hotter.
A school of fish swim through a break in the coral along the Great Barrier Reef in Australia.
“You’ve got this relentless rise of greenhouse gases in the atmosphere,” said senior scientist at the National Oceanic and Atmospheric Administration Michael McPhaden. “We just know unless that turns around in some way, we will continue to set records.”
Historically, El Niño is known for accelerating global warming, with devastating effect. The pattern is marked by warmer-than-average surface waters in the Pacific Ocean that have domino effects on weather around the world. The last major El Niño drove the planet to record heat in 2016. The legacy of El Niño includes severe drought in places such as Indonesia and southern Africa, increased precipitation along the southern United States (US), and diminished Atlantic hurricane activity.
Strong El Niños can also trigger ecological disasters and deadly weather extremes: drought and wildfires that cause rainforest loss, ocean warming that kills aquatic life and bleaches corals, rapid loss of polar ice, and a surge in transmission of diseases such as the plague.
Now, scientists see signs of another El Niño brewing as Pacific waters off Ecuador and Peru quickly warm up. It is there that El Niño got its name, because the warming is known to disrupt the region’s fishing industry around Christmas.
Climate forecasters estimate a 62 per cent chance El Niño develops sometime between May and July, and a 90 per cent chance it arrives by the end of the year.
It would be a stark change after three years dominated by El Niño’s counterpart, La Niña – an unusually long stretch that scientists say ended in February. That extended La Niña may be contributing to the rapid warming being observed now, Kevin Trenberth, an ocean expert and scholar at the National Center for Atmospheric Research, said in an e-mail.
In contrast to El Niño, La Niña is associated with cooler-than-normal surface waters in the tropical Pacific. That means a lot of the oceans’ heat is “buried” in deeper waters during La Niña, Trenberth said.
As El Niño develops, it may be bringing that heat back to the surface.
That suggests the spike in ocean temperatures may ease as the heat is released through evaporation, Trenberth added. Similar warming was observed in early 2014, but El Niño did not arrive until fall 2015, eventually strengthening dramatically into the following year.
Trenberth said the recent shifts are “indeed signaling the likely beginning of the next major basin-wide El Niño event developing this year and likely leading to new highs in global mean surface temperatures in 2024”.
Specific impacts from the rapid warming are not yet known, but they may be limited so far, given that the heat of summer is winding down in the Southern Hemisphere and has not yet arrived in the Northern Hemisphere, said Regina Rodrigues, who studies marine heat wave impacts at the Federal University of Santa Catarina in Brazil.
When marine heat waves hit during the summer, they can cause massive die-offs among aquatic creatures and vegetation.
The recent surge in ocean temperatures, while startling, follows on a decades-long trend of rising heat in the world’s oceans, which scientists say have absorbed 90 per cent of the excess heat in the Earth’s system in recent decades due to rising greenhouse gases.
The ripple effects of hotter oceans can be far-reaching and dramatic. Warmer water raises the odds of ocean heat waves in certain regions of the globe, with potentially catastrophic consequences for marine life.
A warmer ocean also means an expanding ocean, raising sea levels that affect coastlines and worsen flooding. Warmer water at the top levels of the ocean can also help fuel more intense storms and the torrential rainfall that accompanies them.
“Those upper sea surface temperatures have really serious consequences for any storm that comes along,” Trenberth told The Post in a January interview.
In part, that is because more heat amounts to more moisture in the air, which can supercharge any storms that materialise.
For every degree Fahrenheit that the air temperature increases, the atmosphere can hold about four per cent more water.
Scientists have found that ocean warming, while strong and steady overall, varies around the globe – with particularly rapid increases in heat in the Atlantic region off the US coastline. This is amplifying coastal sea level rise and may also be implicated in a strong warming trend affecting the coastal northeastern US on land.
But research has continued to mount that on the whole, the oceans are steadily growing warmer.
A study published in October in Nature Reviews found that the upper reaches of the oceans have been heating up around the planet since at least the 1950s, with the most stark changes observed in the Atlantic and Southern oceans.
The authors wrote that data shows the heating has both accelerated over time and increasingly has reached deeper depths. That warming is likely irreversible this century, the scientists said, and will almost certainly continue to worsen if humans don’t make significant and rapid cuts to greenhouse gas emissions.
In its most recent assessment, the United Nations Intergovernmental Panel on Climate Change (IPCC) wrote that it is “virtually certain” that the upper levels of the oceans have warmed over the past half-century and “extremely likely that human influence is the main driver”.
Human-caused emissions “are the main driver of current global acidification of the surface open ocean”, the panel wrote.
The greenhouse gas emissions that humans have produced since 1750 “have committed the global ocean to future warming,” the IPCC authors found. Over the remainder of the 21st Century, the group said, ocean warming will probably be several times what it has been over the past five decades.
All of those trends make the prospect of a new El Niño, and its warming influence, more alarming. Scientists suspect climate change is making El Niño more extreme, less predictable and potentially more consequential for the planet.
“The energy accumulated in the water from increasing the heat in such a drastic way during El Niño years does not dissipate easily,” said David Costalago, a marine scientist with the advocacy group Oceana. Costalago said that may only add to the exponential increase in warmth fuelled by human-driven climate change.
Regardless of whether El Niño officially materialises this year, the climate will continue to change, McPhaden said.
“These ups and downs related to La Niña and El Niño, they are temporary,” he said. “The real issue is the rising greenhouse gas concentrations in the atmosphere, which are going up and up and up.”
