The West Coast in the United States is warm and parched. The East Coast spent the past winter cold and snowed under. What’s the cause of all this mayhem?
Two new studies suggest a long-lived patch of warm water off the West Coast, about 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) above normal, may be at least partly responsible.
“In the fall of 2013 and early 2014 we started to notice a big, almost circular mass of water that just didn’t cool off as much as it usually did, so by spring of 2014 it was warmer than we had ever seen it for that time of year,” says Nick Bond, a climate scientist at the Joint Institute for the Study of the Atmosphere and Ocean, a joint research center of the University of Washington and the US National Oceanic and Atmospheric Administration.
The huge patch of water—1,000 miles in each direction and 300 feet deep—had contributed to Washington’s mild 2014 winter and might signal a warmer summer.
Less cooling, not more heating
Ten months later, the patch, what Bond dubbed “the blob,” is still offshore, now squished up against the coast and extending about 1,000 miles offshore from Mexico up through Alaska, with water about 2 degrees Celsius (3.6 degrees Fahrenheit) warmer than normal. All the models point to it continuing through the end of this year. Bond says.
Findings published in Geophysical Research Letters and funded by NOAA, suggest the blob relates to a persistent high-pressure ridge that caused a calmer ocean during the past two winters, so less heat was lost to cold air above. The warmer temperatures we see now aren’t due to more heating, but less winter cooling.
The study warns that the blob is affecting West Coast marine life: fish have been seen in unusual places, supporting recent reports that West Coast marine ecosystems are suffering and the food web is being disrupted by warm, less nutrient-rich Pacific Ocean water.
The blob’s influence also extends inland. As air passes over warmer water and reaches the coast it brings more heat and less snow, which the paper shows helped cause current drought conditions in California, Oregon, and Washington.
The mass is just one element of a broader pattern in the Pacific Ocean whose influence reaches much further—possibly to include two bone-chilling winters in the Eastern United States.
Another study in the same journal by Dennis Hartmann, professor of atmospheric sciences, looks at the Pacific Ocean’s relationship to the cold 2013-14 winter in the central and eastern United States.
Despite all the talk about the “polar vortex,” Hartmann argues we need to look south to understand why so much cold air went shooting down into Chicago and Boston.
Second to El Niño
His study shows a decadal-scale pattern in the tropical Pacific Ocean linked with changes in the North Pacific, called the North Pacific mode, that sent atmospheric waves snaking along the globe to bring warm and dry air to the West Coast and very cold, wet air to the central and eastern states.
“Lately this mode seems to have emerged as second to the El Niño Southern Oscillation in terms of driving the long-term variability, especially over North America,” Hartmann says.
Hartmann says the root cause of weather this past winter was surface temperatures in the tropical Pacific. His research was funded by the National Science Foundation.
That pattern, which also causes the blob, seems to have become stronger since about 1980 and lately has elbowed out the Pacific Decadal Oscillation to become second only to El Niño in its influence on global weather patterns.
“It’s an interesting question if that’s just natural variability happening or if there’s something changing about how the Pacific Ocean decadal variability behaves,” Hartmann says. “I don’t think we know the answer. Maybe it will go away quickly and we won’t talk about it anymore, but if it persists for a third year, then we’ll know something really unusual is going on.”
Although the blob does not seem to be caused by climate change, it has many of the same effects for West Coast weather, Bond says.
“This is a taste of what the ocean will be like in future decades. It wasn’t caused by global warming, but it’s producing conditions that we think are going to be more common with global warming.”
Source: University of Washington