A large expanse of unusually warm water in the northern Pacific Ocean continues to grow and is having a profound effect upon marine animals from Mexico to Alaska, and may be altering weather across the continent.

“The blob,” a term coined by University of Washington meteorologist Nicholas Bond, who was among those who first observed it in late 2013, consists of  water that is roughly around 5 degrees Fahrenheit warmer than the typical ocean temperature.

While that may not seem like much of a difference, the circular patch of warmth, which started as a small patch of water off the coast of Alaska, has grown to 500 miles across,and is the biggest and longest-lasting temperature anomaly in the historical record.

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“Just the enormous magnitude of this anomaly is what’s incredible,” Art Miller, an oceanographer at the Scripps Institute of Oceanography in La Jolla, Calif., told the San Jose Mercury News. Miller was among a group of 100 researchers who gathered recently at Scripps to discuss the phenomenon and its impacts.

Scientists aren’t sure exactly what caused the blob, but they think it may have links to everything from the California drought to the large numbers of starving sea lion pups who’ve washed up on west coast shores.

The temperature change also has caused creatures from tropical and temperate zones to wander north into places where they’re not usually found, and others that normally stay far out at sea have ventured closer to the coast, according to this Seattle Times article. 

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In an article for Earth and Sky in April, Bond wrote that the blob is related to an unusual weather pattern that developed over a huge region of the Earth, extending from the northern Pacific across North America, in the fall of 2013 and early 2014.

The pattern featured a higher-than-normal pressure ridge off the coast of the Pacific Northwest, which Bond says reduced the number and intensity of storms that made landfall, and led to reduced precipitation in the western United States.

But the ridge also affected weather farther east, Bond wrote, by diverting cold Canadian air into the middle and eastern U.S., especially around the Great Lakes region.