‘Uncharted territory’: Warming oceans and disappearing sea ice alarm scientists

There has been a wave of new research and warnings related to the oceans and climate change this year. Little of the news is good.

Almost 90 percent of the heat added to the Earth system between 1971 and 2020 has gone into the ocean. When the sun shines, it warms the air, water, and soil. But the Earth also reflects and releases heat back into space. If the amount of incoming solar radiation is greater than outgoing radiation, then it creates an energy imbalance. And boy is our world out of whack.

Researchers have recently determined that the Earth has added approximately 381 zettajoules of heat between 1971 and 2020. A zettajoule is an almost unfathomably large number—one sextillion (that’s a one followed by 21 zeroes) of the standard metric measure of energy known as the joule. To put this enormous amount of energy into perspective, courtesy Alex Wellerstein’s handy Hiroshima-equivalent calculator: Since 1971, the Earth has absorbed the heat equivalent of over 6 billion atomic explosions of the size that decimated Hiroshima in 1945, give or take a few explosions.

Most of this heat—89 percent of it—has gone into the ocean. All things considered, it might be more accurate to call global warming, ocean warming.

The researchers, led by Karina von Schuckmann, also confirmed previous findings that the rate of global heating has increased since 2006. Additional research published earlier this year showed that the ocean in 2022 was hotter than ever before recorded. The ocean heat content was greater by almost 10 zettajoules (approximately 159 million Hiroshima-equivalents) than in 2021, which had previously held the distinction of hottest ocean year on record.

This general trend has continued into 2023; ocean sea surface temperatures in late March and April were the highest ever recorded. “Usually when you have a particular warming event, we’re beating the previous record by a little bit,” Robert Rohde, a scientist at Berkeley Earth, told Wired. “Right now we’re sitting well above the past records for this time of year, for a considerable period of time.”

Sea ice is declining at both poles. The amount of Antarctic sea ice is lower now than it has been in four decades at the same time of year. The current total sea ice coverage is about 1.8 million square kilometers (roughly the area of the country of Libya) smaller than average.

Seen in the visualization below, the current sea ice anomaly—or deviation from the norm—is even more striking.

Until 2016, average sea ice coverage in Antarctica had been slightly increasing over the previous four decades, Zachary Labe, a postdoctoral research associate at Princeton University and NOAA Geophysical Fluid Dynamics Laboratory, tells the Bulletin. But in 2016, the sea ice levels dropped precipitously to record lows in October, November, and December. Researchers have attributed this to changing wind patterns and warmer ocean temperatures.

Labe explains that sea ice has been insulating the Antarctic ice sheet (the ice covering Antarctica’s land mass) and giant ice shelves (the part of the ice sheet that extends over ocean water) from warmer ocean temperatures. The fear is that if sea ice coverage continues to decline, the Antarctic ice sheet would be more exposed to warmer water and air, which could cause it to fracture and melt, leading to drastic and dramatic sea level rise around the globe.

Sea ice at the other pole isn’t faring much better.

A paper published in Nature Communications this week found that the sixth assessment report of the Intergovernmental Panel on Climate Change underestimated the speed at which summer sea ice in the Arctic is declining. Now, researchers project that within the next two decades, summer sea ice in the Arctic could be completely nonexistent for the first time in human history. Even if greenhouse gas emissions are significantly reduced, Arctic summer sea ice is expected to disappear by the middle of the century.

“Unfortunately, it has become too late to save Arctic summer sea ice,” Professor Dirk Notz, a member of the research team from the University of Hamburg, Germany, told the Guardian. “As scientists, we’ve been warning about the loss of Arctic summer sea ice for decades. This is now the first major component of the Earth system that we are going to lose because of global warming. People didn’t listen to our warnings.”

How this change could impact carbon cycling and storage in the Arctic Ocean remains poorly understood.

Meltwater is changing ocean currents. What’s more certain is that the meltwater in Antarctica is changing the circulation patterns in the ocean. As the ice in Antarctica melts, it introduces more freshwater into the ocean. Global ocean circulation patterns are driven by dense (salty) cold water sinking to the bottom of the ocean and displacing warmer waters. The melting fresh water from Antarctica is interfering with that process.

Researchers say signs of a slowdown in deep ocean circulation are already visible, and warn that a dramatic slowdown or even complete collapse could happen this century.

“The model projections of rapid change in the deep ocean circulation in response to melting of Antarctic ice might, if anything, have been conservative,” Steve Rintoul, an oceanographer and one of the researchers behind these recent studies, told the Guardian. “We’re seeing changes have already happened in the ocean that were not projected to happen until a few decades from now.”

Previously, concerns about meltwater and changing ocean circulation patterns were focused on the North Atlantic, Fred Pearce reports for Yale Environment 360. But this new research shows that changes in the Southern Ocean are as or even more concerning.

If ocean circulation collapsed, it would inhibit the exchange of nutrient-dense waters from the ocean floor to the surface, with potentially devastating consequences for marine life, and interfere with the process by which the ocean sequesters carbon, potentially accelerating global warming.

Writing about their research in The Conversation, the scientists did not mince words: “Climate change is to blame.”

El Niño on the horizon. On top of these long-term trends, scientists are predicting that an El Niño event will develop this year. The tropical Pacific Ocean goes through warmer and cooler periods roughly every two to seven years. El Niño years are characterized by warmer water temperatures along the equator in the Pacific Ocean, which in turn shift global climate patterns.

“A warming El Niño is expected to develop in the coming months and this will combine with human-induced climate change to push global temperatures into uncharted territory,” the secretary-general of the World Meteorological Organization, Petteri Taalas, said in a statement last month. “This will have far-reaching repercussions for health, food security, water management, and the environment. We need to be prepared.”

What’s especially alarming, Labe explains, is that the record-breaking ocean temperatures seen in 2021 and then again in 2022 occurred in La Niña years, when the Eastern Pacific is colder than usual. This is believed to have masked some of the impacts of global ocean warming the past few years.

“[Because of] climate change, just everything you see is sort of amplified at this stage,” Labe says. “’How strong is this El Niño gonna be?’ is very much an open question.”

The BBC reported that some of the scientists they contacted for comment on recent observed ocean warming were reluctant to go on the record. One summed up their feelings as “extremely worried and completely stressed.”

Climate change and ocean warming could even be a factor behind the wildfires that have blanketed the East Coast in smoke this week.

“One area of research that is still an open question is sort of how [climate change and warming oceans] relate to what we call blocking patterns,” Labe says. “What that essentially means is that the atmosphere kind of slows down, which causes long persistent events. This blocking phenomenon is a natural occurrence, but we’re trying to understand whether these persistent events sort of become amplified due to climate change.”

Longer duration wet and dry events are predicted to increase if world temperatures surpass 2 degrees Celsius of warming above pre-industrial levels.

“Why we care about that is because it really affects extremes,” Labe added. “Like right now, we’ve seen a very persistently dry and hot conditions over Canada. And because of that, we’re having all these wildfires and smoke pouring across all of North America.”