The Pacific Ocean may have entered a new warm phase — and the consequences could be dramatic

פורסם: 22 באפר׳ 2015, 12:03 על ידי: Sustainability Org   [ עודכן 23 באפר׳ 2015, 0:00 ]
By Chris Mooney April 10 2015


Two new studies have just hit about the “warm blob” in the northeast Pacific ocean — a 2 degree C or more temperature anomaly that began in the winter of 2013-2014 in the Gulf of Alaska and later expanded. Scientists have been astonished at the extent and especially the long-lasting nature of the warmth, with one NOAA researcher saying, “when you see something like this that’s totally new you have opportunities to learn things you were never expecting.”

The Post’s Sarah Kaplan has covered some of the most immediate consequences of the “blob,” such as weird appearances of strange marine species more typical of warm water, like ocean sunfish, off the Alaskan coast. She also notes that the blob may be linked to the California drought and other odd weather phenomena.

[In the red: West coast waters are warmest in decades — what does it mean for winter?]

That’s plenty dramatic enough — but in truth, there is a great deal more to say about what this phenomenon may mean in a global climate context.

You see, the 2013-2014 “blob” was just the beginning. In the summer of 2014, warm water also showed up off the California coast. And then, in the fall of last year, “a major change in the wind and weather pattern between Hawaii and the West Coast caused the two warm blobs to merge and expand to fill the entire northeast Pacific Ocean,” says Nate Mantua of NOAA’s Southwest Fisheries Science Center, a co-author of one of the new studies, by e-mail.

According to Mantua, the emergence of the new and consolidated “blob” may be a very significant development with global consequences. That’s because it may relate to a much larger pattern of ocean temperatures called the Pacific Decadal Oscillation, or PDO. A shift in this oscillation, in turn, may be a sign that the planet is on the verge of getting warmer, some scientists say.

“People are seeing a lot of ecological impacts related to this warm water, and people are looking for the story, why is this happening, what is it?” Mantua says. “And it, to me, looks like just an extreme shift into the warm state of the PDO.”

The PDO is kind of like a far more long-term version of the much better known El Niño-La Niña cycle. It is not thought to be related to global warming — rather, it is believed to be the result of “natural internal variability” in the climate system.

The oscillation has a positive phase and negative phase. And according to NOAA’s Climate Prediction Center, we have been in a positive phase for nine months straight, dating back to July 2014. Here’s a visualization of the PDO cycle from the National Climatic Data Center — and note the uptick at the far right:

Mantua also keeps an index of the PDO, and he says that at the moment, “my version has much more extreme positive values than theirs has.” But generally, the two indices are telling the same story, he says.

“In 2014 it went from mostly negative values to a very strong expression of the warm phase, and that’s present today,” Mantua says.

If the PDO is not only positive but is going to stay that way, it could be a big deal. Here’s why: Some scientists think a persistent cool phase of the PDO cycle may be a key part of the reason why there has been a much discussed “slowdown” of global surface warming recently. And if they’re right about that, then with the end of the cool phase, we may also see an end to any global warming “hiatus.”

[The global warming slowdown is real — but that’s no reason to question climate science]

The reason is the way the PDO works. While any such planetary scale wobble has multiple ramifications, one of them is the way it influences the distribution of heat between the ocean and the atmosphere.

“When you’re in a cool phase, heat from the atmosphere gets buried in the ocean,” says John Abraham, a climate scientist at the University of St. Thomas in Minnesota. “When you’re in a warm phase, that heat comes out. And we’ve just switched from a cool to a warm phase.”

Indeed, Kevin Trenberth and John Fasullo, two climate researchers at the National Center for Atmospheric Research in Boulder, Colo., have argued that the PDO helps explain the alleged global warming “pause” through a mechanism of heat sinking deep down into the Pacific:

The picture emerging is one where the positive phase of the PDO from 1976 to 1998 enhanced the surface warming somewhat by reducing the amount of heat sequestered by the deep ocean, while the negative phase of the PDO is one where more heat gets deposited at greater depths, contributing to the overall warming of the oceans but cooling the surface somewhat.

The alleged “pause,” say Trenberth and Fasullo, coincided with a negative phase of the PDO in the 2000s.

That’s why Trenberth has further argued that the new apparent shift back into the PDO’s positive phase may mark the beginning of a temperature ramp-up. As he explains by e-mail:

Instead of thinking of global warming as providing a steady relentless climb in global temperatures, one should think of it more as an up staircase. So we may well have gone up the next step, and then we vary up and down a bit but around a whole new level, never to go back down to previous lows.  The odds are quite good that this is what has happened.

A study recently published in Science made a similar point, highlighting that a “sharply negative-trending” Pacific oscillation had helped to undermine global warming of late. But as it added, “Given the pattern of past historical variation, this trend will likely reverse with internal variability instead, adding to anthropogenic warming in the coming decades.”

Granted, there’s ample reason for caution here. The PDO has only been known about since the year 1997, when scientists studying booming salmon runs in Alaska identified the phenomenon as part of a much more vast global pattern. Mantua, the lead author of the original PDO paper, has continued to study the matter and emphasizes that there’s still a lot we don’t know about the cycle, especially when it comes to forecasting its future states.

“The mechanisms that really drive its evolution don’t seem to have a lot of predictability beyond about a year,” he says.

Braddock Linsley, a scientist at Columbia’s Lamont-Doherty Earth Observatory who has been studying the southern hemisphere ramifications of the PDO, similarly warns that it is “not like a clock.” While nominally a 20-or-so year cycle, as you can see from the figure above, the PDO doesn’t play by strict rules.

So in sum — there’s some oddness happening in the Pacific right now, including very warm water off the U.S. coast and what looks like a shift in the PDO. And some scientists think this could lead to a step-change upwards for global warming, and the end of the so-called pause or slowdown. But there’s also plenty of uncertainty; Trenberth, who told the climate blogger Joe Romm recently that he thought we were in for a new uptick in temperatures, also commented there that he was “sticking my neck out.”

So for now, I’ll just leave you with an indisputable point — namely, the Pacific Ocean is sublimely gigantic, so it’s no surprise that what happens there can have ramifications everywhere. And scientists are now examining those changes very closely indeed — because they know how much they might matter.