The Weekend Wonk: Arctic Ice/Jetstream -The Real Climate Debate

March 1, 2014

I spoke last fall at the Local Futures conference in Northern Michigan, and organizer Aaron Wissner clipped and uploaded a portion of my talk – where I mentioned the current discussion about climate, jet stream behavior, and arctic sea ice.
I think it’s good, and accurate, but I would probably restate when I said  “everybody agrees there is something wrong with the jet stream, and there is an emerging agreement that it has to do with the loss of arctic ice”.  Dr. Kevin Trenberth would pillory me for that one – I went too far.

What I should have said was, there is general agreement that we are in “a new normal”, some of that is manifesting in extreme weather events, – many of which are related to atypical jet stream behavior, but there are differing views as to primary drivers of that change. Below, Dr. Francis and Dr. Jeff Masters describe the basics of the “weather whiplash” idea.

In the last few weeks, this debate has moved out from the hallways at scientific conferences, into a mass media stage.  I’m somewhat – well, actually quite a bit – proud, that I presented the first online discussion between two of the major players, Dr. Jennifer Francis, and Dr. Kevin Trenberth, almost a year ago in the “This is Not Cool” video series, before it rose to media kerfuffle status.

In recent weeks, we’ve seen a letter, signed by several major, experienced climate experts, including Dr. Trenberth, appear in Science magazine. cautioning about too much media attention focused on the “climate change may mean colder winters” idea

IN MID-JANUARY, A LOBE OF THE POLAR VORTEX SAGGED SOUTHWARD OVER THE CENTRAL and eastern United States. All-time low temperature records for the calendar date were set atO’HareAirportinChicago[–16°F(–27°C),6January],atCentralParkinNewYork[4°F (–15.6°C), 7 January], and at many other stations (1). Since that event, several substantial snow storms have blanketed the East Coast. Some have been touting such stretches of extreme cold as evidence that global warming is a hoax, while others have been citing them as evidence that global warming is causing a “global weirding” of the weather. In our view, it is neither.

As climate scientists, we share the prevailing view in our community that human-induced global warming is happening and that, without mitigating measures, the Earth will continue to warm over the next century with serious consequences. But we consider it unlikely that those consequences will include more frigid winters.

Referring to a very influential paper by Jennifer Francis and Stephen Vavrus – which posited an influence on weather extremes, stemming from the loss of arctic sea ice and knock-on effects on the jet stream – the Science letter went on:

..the notion that the demise of Arctic sea ice during summer should lead to colder winter weather over the United States seems counterintuitive. But that is exactly what an influential study has suggested (2). The authors hypothesize that global warming could perturb the polar vortex in a manner that renders the flow around it more wavy, leading to an increased incidence of both extreme warmth and extreme cold in temperate latitudes. It’s an interesting idea, but alternative observational analyses and simulations with climate models have not confirmed the hypothesis, and we do not view the theoretical arguments underlying it as compelling.

The letter was the basis for an article in the Washington Post – which described how Francis/Vavrus was being depicted in the media, and even the President’s Science advisor, perhaps too readily, as an explanation for the current wave of cold weather in the eastern US.

Despite this pushback, numerous mainstream press outlets have written about the Francis theory uncritically, failing to present countervailing views.

For example, from the BBC:

The main system that helps determine the weather over Northern Europe and North America may be changing, research suggests.

The study shows that the so-called jet stream has increasingly taken a longer, meandering path.

And from NPR:

The wayward jet stream could account for the persistently severe winter weather this year in the U.S. and Britain, as well as California’s long drought.

Even the White House’s science advisor, John Holdren, expressed support for the theory with only subtle qualification.

“I believe the odds are that we can expect as a result of global warming to see more of this pattern of extreme cold in the mid-latitudes and some extreme warmth in the far north,” says Holdren in a YouTube video.

The truth is that cold extremes are in the midst of unmistakable decline in the U.S. As the Science magazine letter notes:

Cold air outbreaks even more severe than occurred this winter affected the United States in the early 1960s, the late 1970s (most notably 1977), and in 1983, back when the Arctic sea ice was thicker and more extensive than it is today… Over the longer time span of 50 to 100 years, it is well established that there has been a decrease in the rate at which low temperature records are being set relative to all-time high temperature records at stations across the United States.

For her part, Dr. Francis agrees that the “global warming/cold winter” angle has been over-amped in the media, but defends the main thrust of her paper. In a response on Andrew Revkin’s blog she wrote:

The media certainly had a field day with the “attack of the polar vortex” in early January, and in their hyping of the story, some misquoted me (and others) by saying that climate change caused the unusual cold spell. Of course this sort of event has happened before, and this one wasn’t unprecedented.

I also agree that greenhouse-gas induced warming will reduce, not increase, the likelihood of breaking cold temperature records — the data already show this.

The misinterpretation and criticism of her work notwithstanding, Francis stands by her theory that, even as climate stays on a warming course, an erratic jet stream will bring greater weather variability. In her remarks to Revkin, she uses this year’s dramatic weather pattern as a case in point:

….the amazing persistence of this winter’s highly amplified pattern is an example of this behavior, but of course it can’t be blamed on any one factor. Even though the cold in the U.S. has not been unprecedented, the public perception is “extreme” because the cold in the central/eastern/southeastern U.S., drought in California, and the heat/heavy precipitation in Alaska has been so prolonged. This is exactly the type of “extreme” we refer to in our paper, not the record-breaking-temperature sort.

This week, one of the Science letter authors has a guest spot in the Washpost Capitol Weather Gang, further expanding on the critique.

At many tropical stations, the mean temperature of the past few decades lies within the top quartile of the probability distribution of temperature at those same stations a century ago. But at sites in middle latitudes, the internal variability of the climate system swamps the human-induced global warming trend, especially during wintertime. That’s why low temperature records are still being set occasionally, even in a warming climate.

I disagree with those who argue that we need to capitalize on recent extreme weather events to raise public awareness of human-induced global warming. Many of the reporters who write stories about our research don’t recognize the distinction between the broad scientific consensus on climate change and the various unsubstantiated hypotheses relating to extreme weather events. When the public becomes confused, the carefully considered scientific consensus becomes vulnerable to attack by the apologists for economic growth at all costs. It didn’t take them long to learn that poking fun at the notion that global warming could lead to extreme cold is an effective tactic.

Fair enough.
OK, here’s my take.

The Science letter is, it seems to me, stuck on the media conversation, which seems to have become “scientists say that global warming may cause colder winters” –— which is – this is critical – not what Francis/Vavrus says – there needs to be a reminder that the paper simply posits

“..increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.”

and mentions

..”persistent weather conditions associated with recent severe events such as the snowy winters of 2009/2010 and 2010/2011 in the eastern U.S. and Europe, the historic drought and heat-wave in Texas during summer 2011, or record-breaking rains in the northeast U.S. of summer 2011..”

This week I’ve had conversations with two scientists in particular, who, in 2004, published a study modeling the effects of arctic ice loss on global precipitation and temperature. That study produced some figures are remarkable in that they speak not only to the current California drought, but to the jet stream pattern that associated with that drought, as well as cold extremes in the east, and the repetitive storms battering the UK.
I’m working on a drought piece that I hope will incorporate some of those ideas, so stay tuned.

In the meantime, remember that this blog is the place where you’ll get a heads up on the real conversations of climate scientists, long before they make headlines elsewhere.

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15 Responses to “The Weekend Wonk: Arctic Ice/Jetstream -The Real Climate Debate”


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