The Pacific Ocean is running a fever. Why that’s an ominous sign.
A marine heat wave covering an area eight times the size of the United States could soon fuel serious storms and extreme heat.
Across the Pacific Ocean, there’s a massive marine heat wave covering an area more than eight times the size of the contiguous United States — and it could have profound ripple effects for weather events around the globe in the coming weeks and months.
This area makes up about 13.5 percent of Earth’s total surface, stretching from the Philippines to Peru — where people are flocking to the beach during the Southern Hemisphere winter — and northward to the coasts of Hawaii and California.
Marine heat waves are a strong, sprawling and sustained warming in the ocean, sometimes near the surface and other times extending deep. They are ranked on a scale from 1 (moderate) to 5 (beyond extreme), reflecting both their intensity and duration.
The enormous Pacific marine heat wave formed as two separate marine heat waves combined: one in the North Pacific and another associated with a developing super El Niño along the equator.
While warmer seas might sound nice to some beachgoers, what happens in the ocean doesn’t stay in the ocean — and this marine heat wave is an ominous sign for weather patterns to come.
“Months and months of warmth could mean stark impacts this winter and next spring,” said climate scientist Dillon Amaya, who has been closely monitoring the warmth near California.
How this ocean fever could affect the weather
Two significant weather events in the next two weeks are connected to this marine heat wave: a super typhoon in the western Pacific Ocean and the potential for a profound heat dome in the western United States during mid-July.
The typhoon, named Bavi, will be powered by the bathtub-like warmth of the western Pacific. This dangerous storm will pass near the Northern Mariana Islands, north of Guam, on Monday local time and could also bring destructive impacts to Taiwan and China late in the week.
Meanwhile, thunderstorms bubbling over the marine heat wave could promote the formation of a powerful heat dome thousands of miles away in the western U.S. during mid-July, sending temperatures soaring there.
Defense Department meteorologist Eric Webb said in an X post that this pattern could “greatly increase heat/wildfire risks north of New Mexico and Arizona.” That’s an area where wildfires have recently been raging.
But there may be much more extreme weather after that.
In a recent live stream, climate scientist Daniel Swain said the very warm Pacific seas are expected to drive sea levels 6 inches to 2 feet higher near California.
Winds from storms this fall and winter will elevate the sea even more, potentially resulting in dangerous rises of 2 to 3 feet or more near the California coast.
“This is the time for local governments, for county governments and for the state government to start to prepare for a significant likelihood of much higher than average sea levels, more disruptive coastal flooding and potentially record-breaking coastal water levels during winter storm events and king tide events,” Swain said.
“This coming winter, right now, does look like one where there’s an increased likelihood of historically unusual to unprecedented rain and storm events,” Swain said.
But he stressed that while the odds for such scenarios are higher, they are not guaranteed.
California isn’t the only place that could experience such profound effects.
The vast amount of heat stretching across the Pacific will be released into the atmosphere above, turbocharging the subtropical jet stream from fall into winter. That may form a storm highway across the southern and eastern United States, elevating the potential for flooding rainfall and severe thunderstorms.
This ocean fever will have global consequences, too. As sea temperatures rise, evaporation increases, adding more water vapor to the atmosphere — which is fuel for extreme rain events.
“Water vapor amounts go hand in hand with sea surface temperatures, mostly,” said climate scientist Kevin Trenberth.
That extra moisture is carried by winds that circulate around high- and low-pressure cells and can be carried thousands of miles from where it originated.
Following a deadly June heat dome, a marine heat wave also recently formed near Europe, including across the Mediterranean Sea. More extreme heat will affect that region into mid-July, with the unusually warm waters helping to reinforce the heat.
The area covered by marine heat waves is surging
Marine heat waves form in different ways. Sometimes, winds weaken and the sea turns calmer, preventing colder water from being churned up to the surface from below. Other times, changes in atmospheric circulation patterns cause more sunshine and fewer clouds, heating up the sea. Changing ocean currents can play a role, too.
The one currently in the Pacific is linked to a natural climate variation called the Pacific Meridional Mode, or PMM, that formed because of weaker winds and less evaporation.
Amaya said that as El Niño continues to grow, it can combine with the PMM to generate massive swaths of heat.
These warm ocean blobs are growing in both coverage and intensity as the climate changes.
“The heat capacity and mobility of water makes the ocean the main sink of excess heat from human-induced heating of the planet, mainly from increasing carbon dioxide and other greenhouse gases in the atmosphere,” Trenberth said.
The portion of the global ocean experiencing marine heat waves has more than tripled since the late 1980s, increasing from about 9 percent to more than 30 percent.
Over that same period, the global coverage of strong to beyond extreme (Category 2 to Category 5) marine heat waves has increased nearly sixfold.
Marine heat waves also spike during El Niño events.
In January 2024, during an El Niño event that contributed to the planet’s warmest year on record, more than 46 percent of the global oceans simultaneously experienced a marine heat wave — the highest amount on record.
Currently, more than 37 percent of the global ocean is covered by a marine heat wave, but a record may be set this year or next as this ocean fever — and its potential impact — intensifies.
The marine heat wave statistics were calculated using data from NOAA’s Coral Reef Watch that extends back to 1985. Trends were calculated by first applying a two-week rolling average to the data. Shapefiles were used to compute the size of the Pacific marine heat wave area relative to the contiguous United States.
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