Across the Pacific Ocean, a massive marine heat wave covers an area more than eight times the size of the continental United States, and could have profound repercussions on weather events around the world in the coming weeks and months. This area represents approximately 13.5% of the Earth’s total surface, stretching from the Philippines to Peru, where people flock to the beach during the southern hemisphere winter, and north to the coasts of Hawaii and California.
Marine heat waves are intense, widespread and sustained warming of the ocean, sometimes occurring near the surface and sometimes extending to great depths. They are classified on a scale from 1 (moderate) to 5 (extreme), according to their intensity and duration. The huge Pacific marine heat wave It formed from the combination of two separate marine heat waves: one in the North Pacific and another associated with a developing super El Niño along the equator. While warmer waters may sound nice to some beachgoers, what happens in the ocean doesn’t stay in the ocean, and this marine heat wave is an ominous harbinger of weather patterns to come.
“Months and months of heat could have serious consequences this winter and next spring,” said climate scientist Dillon Amaya, who has been closely monitoring the heat near California.
How this ocean fever could affect the climate
Two major weather events expected in the next two weeks are related to this marine heat wave: a super typhoon in the western Pacific and the possibility of a deep heat dome in the western United States in mid-July. The typhoon, called Bavi, will feed on the warm, bathtub-like waters of the western Pacific. This dangerous storm will pass near the Northern Mariana Islands, north of Guam, and could wreak havoc in Taiwan and China by the end of the week.
Meanwhile, thunderstorms forming over the marine heat wave could favor the formation of a powerful heat dome thousands of miles away in the western United States in mid-July, causing un rapid increase in temperatures in that area. Department of Defense meteorologist Eric Webb said in an X post that this pattern could “significantly increase heat and wildfire risks to northern New Mexico and Arizona.” That is an area where devastating wildfires have recently been recorded. But much more extreme weather events are possible later.
In a recent live broadcast, climatologist Daniel Swain said that extremely warm temperatures in the Pacific are expected to raise sea levels between 15 centimeters and 60 centimeters near California. Winds from this fall and winter storms will further raise sea levels, which could lead to dangerous rises of 2 to 3 feet or more near the California coast. “Now is the time for local governments, county governments and state government to begin preparing for a significant probability of much higher than average sea levels, more devastating coastal flooding and potentially record-breaking coastal water levels during winter storms and spring tides,” Swain said.
“This coming winter, as things stand, looks like it will have an increased chance of historically unusual or unprecedented rain and storms,” Swain said. But he stressed that, although the probabilities of such scenarios occurring are greater, they are not guaranteed.
California isn’t the only place that could experience such profound effects. The enormous amount of heat spreading across the Pacific will be released into the atmosphere, intensifying the subtropical jet stream from fall to winter. This could form a storm zone across the southern and eastern United States, increasing the risk of heavy rain and intense thunderstorms. This ocean fever will also have global consequences. As sea temperatures rise, evaporation increases, adding more water vapor to the atmosphere than in turn feeds the phenomena of torrential rains. “The amount of water vapor goes hand in hand with sea surface temperature, in most cases,” said climatologist Kevin Trenberth.
This additional moisture is transported by the winds that circulate around the high and low pressure cells, and can travel thousands of kilometers from its place of origin. Following the devastating heat wave that hit the region in June, another marine heat wave recently formed near Europe, affecting the Mediterranean Sea. The extreme heat will continue in that area until mid-July, and the unusually warm waters will help intensify it.
The area affected by marine heat waves is increasing
Marine heat waves form in a variety of ways. Sometimes the winds weaken and the sea calms, preventing cold water from rising to the surface. Other times, changes in atmospheric circulation cause more sun and fewer clouds, warming the sea. Ocean currents can also play a role. The one currently found in the Pacific is related to a natural climate variation called the Pacific Meridional Mode, or PMM, which formed due to weaker winds and less evaporation. Amaya stated that, as that El Niño continues to developcan combine with the PMM to generate enormous heat waves.
These masses of warm ocean water are growing in both extent and intensity as the climate changes. “The heat capacity and mobility of water make the ocean the primary sink for excess heat from human-caused global warming, primarily due to increases in 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, rising from about 9% to more than 30 percent. dDuring that same period, global coverage of intense or even extreme marine heat waves (from category 2 to category 5) has multiplied almost sixfold. Marine heat waves also intensify 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% of the world’s oceans simultaneously experienced a marine heat wave, the largest amount on record to date. Currently, more than 37% of the world’s oceans are 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.