Two giant warming patterns are brewing in the Pacific and warping US weather |
Two giant warming patterns are brewing in the Pacific and warping US weather
A rare but powerful combination of an immense Pacific Ocean heatwave and a "super El Niño" are set to have profound effects on US weather and marine life this autumn. Here are five changes to expect.
In the north-east Pacific Ocean, an immense and persistent heatwave is wreaking havoc on marine life and weather patterns.
"It's a really bright red eyeball in the Pacific," says Andrew Leising, a research oceanographer at the US National Oceanic and Atmospheric Administration (Noaa). "It's huge, it stretches across the whole [ocean]." The Pacific heatwave, which formed in May 2025, is already bringing surface temperatures 3-4C (5.4-7.2F) above average for this time of year, according to Leising.
Add to that: a massive warming pattern known as El Niño is brewing further south. El Niño is a weather phenomenon that pushes up global temperatures, and it is also supercharging Pacific Ocean warming. It is expected to intensify this autumn to become the strongest El Niño in living memory.
This combination of a massive marine heatwave and a "super El Niño" is rarely seen. Here are five impacts we can expect to see – and where they will happen.
1. California: More storm surges, intense floods
California, which has been in the grips of a marine heatwave since December, is bracing for more storm surges and flooding over the autumn and winter due to warmer coastal waters. Coastal water levels are already 15cm (5.9in) above mean sea level, says Patrick Barnard, research director of the Center for Coastal Climate Resilience at the University of California, Santa Cruz. During this El Niño, that already high sea level will soar further still: to at least 15-30cm (5.9-11.8in) higher than normal, says Barnard.
"Every 5-10cm [1.9-3.9in] of mean sea level rise doubles the flooding frequency for most coastal communities along the US West Coast, so with all these expected sea level increases peaking this winter, we will have historically high flood risk," he says.
Warmer ocean surfaces also evaporate more heat and moisture into the air, which can cause heavier rainfall, says Leising. This can lead to more atmospheric rivers – huge, invisible ribbons of water vapour in the sky – in the coming months. These raise the risk of heavy inland flooding and mudslides in California too.
El Niño is a natural phenomenon which occurs when sea surface temperatures in the Pacific Ocean are 0.5C (0.9F) higher than normal for several consecutive months. When the increase is 2C (3.6F), a "very strong" or "super" El Niño occurs.
2. Pacific Northwest US and Canada: Less snowfall, risk of drought
Further north in the US and in Canada, the combined impact of El Niño and marine heatwaves is expected to reduce snowfall, says Larry O'Neill, professor at Oregon State University and director of the Oregon Climate Service. The last huge Pacific marine heatwave, coined "the Blob", led to a record low snowpack in the Pacific Northwest in 2015.
"It may have modified the jet stream........