Nearly all of the world’s oceans are in the midst of “unusual warmth,” warns a leading NOAA scientist who notes this has contributed to the extreme heat baking much of the Northern Hemisphere this summer.
Why it matters: “Even small rises in temperature can disrupt marine ecosystems, cause some species to relocate, and increase disease risks,” said Stats NZ’s Stuart Jones in a statement. “It also contributes to sea-level rise as the warmer water expands.”
Hurricane forecasters warn that record-warm ocean temperatures in the region of the Atlantic — where the most fearsome such storms typically form — could lead to a hyperactive season. Hurricane Beryl, which broke numerous early season records, bore out some of those fears.
The big picture: “This year has observed truly remarkable spatial coverage of above-average sea surface temperatures,” said Zack Labe, a researcher at NOAA’s Geophysical Fluid Dynamics Laboratory.
“The record warmth globally over the last year has been felt both in the atmosphere and in the ocean, which can be directly linked to the influences of human-caused climate change,” Labe said via email.
In fact, June marked 15 straight months of record-shattering ocean warmth, with a chance that July ends that streak with the second-warmest ranking.
The unusually hot waters have led to the globe’s hottest three days on record, beginning on Sunday.
Threat level: The warmer ocean temperatures have impacted ecosystems in both the Northern and Southern Hemispheres. But Labe notes the most anomalous warmth is currently found across the northern half of the Atlantic and Pacific Oceans.
Some of the warmth is connected to marine heat waves, defined as periods of persistent anomalously warm ocean temperatures, which Labe notes are “similar to heatwaves we feel in the atmosphere,” but instead occur in ocean waters.
“These can have major impacts to marine ecosystems, such as through coral bleaching or loss of marine life, and can even affect coastal towns and communities,” Labe said.
Here are some global snapshots:
In the Florida Keys, last summer’s record marine heatwave pushed coral reefs to the brink. While temperatures cooled for a while, they’re now heating back up again.
There’s widespread evidence of coral “paling” but not yet bleaching, said Katey Lesneski, the monitoring coordinator for NOAA’s Mission: Iconic Reefs program, in a call with reporters this week.
Scientists are pursuing plans to put in heat-hardened species on the coral reefs and transplant species from elsewhere, as the southern portion of the Iconic Reefs program is above bleaching thresholds, and the northern areas are nearing this.
“Many of these sites are above that critical threshold” where you start to see them experience heat stress,” according to Lesneski.
New Zealand’s annual sea temperatures are at record highs — increasing 0.16°C-0.26°C (0.28°F-0.47°F) per decade since 1982, according to data out this month from Stats NZ.
Each oceanic and coastal region in the island nation experienced its hottest years ever recorded in either 2022 or 2023, according to the government agency.
Christopher Cornwall, from the Victoria University of Wellington’s School of Biological Sciences noted in a statement that previous intense marine heat waves had killed southern bull kelp in regions along NZ’s coastal South Island, but the effects of such extreme weather events were poorly understood.
“It is highly likely that both the background warming and more frequent, intense, and longer marine heatwaves are already working to permanently alter these marine ecosystems” within New Zealand, he said.
In Croatia, which has been hit by a heat wave on land,the temperature in the Adriatic Sea near Dubrovnik in the country’s south hit 85.5°Fon July 15, which would be the highest temperature on record if confirmed.
Ivica Vilibic, an oceanographer at the Rudjer Boskovic Institute in Split, told Reuters all of the Adriatic was some 5°Cwarmer than what’s typical for this period.
“There are different effects [from climate change]. For example, there are species which like a warm ocean, as in the Red Sea. So there are lot of species that are already coming to the Adriatic, and more will come,” he added.
The intrigue: Cooler sea surface temperatures can be found across the Central Pacific Ocean, which Labe says is a marker of a developing La Niña event. This can modestly cool global temperatures over a short timespan.
Despite this oscillation of ocean temperatures that occurs naturally in the tropical Pacific Ocean, scientists are seeing a long-term increase in sea surface temperatures in this region, too, he said.
Research out just this year “suggests that we may need to consider using alternative definitions for assessing La Niña and El Niño conditions due to this long-term warming of the ocean from climate change,” Labe said.
The bottom line: Georgia Grant, from New Zealand’s Geological and Nuclear Sciences Limited, said in a statement that as the atmosphere “continues to warm with increasing greenhouse gases,” it isn’t surprising the surface of the ocean warms with it.
She noted that the oceans absorb about 90% of the extra heat from the human-caused buildup in greenhouse gases.
“If we didn’t have the ocean,” air temperatures would be 20°C (36°F) higher, Grant added.
