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Study: Arctic Summers Warmest in 600 Years

The Arctic has seen warmer summers over the past two decades than at any time in the past 600 years, according to a study published this week in the journal Nature. The study uses a sophisticated statistical approach, known as Bayesian modeling, to show that the extremely warm summers in high northern latitudes are evidence of an overall warming trend, rather than just a temporary fluctuation in an otherwise unchanging climate.

Surface temperatures in the Arctic were much warmer than average for the first decade of the 21st century, as shown in this image. 
Click on the image to enlarge. Credit: NOAA.

That’s a crucial distinction: a natural fluctuation might reverse before the full effects of warm temperatures could set in, including the melting of Greenland’s ice cap, which could lead to a significant rise in sea level, and ice-free summers in the Arctic Ocean, which could trigger problematic weather anomalies in other parts of the globe.

Scientists have already shown that a warming climate will automatically generate more high-temperature records than a stable one. That’s because individual temperature measurements in a given location form a bell curve, with the greatest number of readings falling into the “normal” range for that location. A small number of readings will fall well above normal, however, and an equally small number will fall below.

If the normal range shifts, however, because the climate is warming overall, high temperatures that once came along very rarely will happen more often, while extreme cold temperatures will become even rarer. A 2012 paper by James Hansen, who recently retired from his post at NASA’s Goddard Institute for Space Studies, showed how this must be true for daily temperatures, but the same principle applies to seasonal averages.

The problem here is that people haven’t been taking comprehensive readings of temperatures in the high Arctic for very long, so they rely on proxies such as tree-ring thickness to stand in for temperature. And those proxies, said lead author Martin Tingley, an expert in climate statistics at Harvard, “carry significant uncertainties.”

Tingley likes to use an analogy: “I’m six-feet-four, which is significantly above average. So even if I’ve never met you, I can confidently guess that I’m probably taller than you are.” But if Tingley were about to enter a room with a thousand men already inside, he couldn’t be equally confident that he’d be the tallest.

It’s the same with summer average temperatures in the Arctic. “From a statistics perspective,” he said, “it’s very different to ask ‘is this summer warmer than the summer of 1473’ and ‘is this summer warmer than all summers in the past 600 years?’”

With precise records, you could just look it up, but the uncertainties in climate proxies make it much more difficult — and without going into the virtues and technical details of different statistical techniques, it turns out that Bayesian analysis is ideally suited to answer that broader question.

The answer, write Tingley and his co-author Peter Huybers, also of Harvard: “…we show that the magnitude and frequency of recent warm temperature extremes at high northern latitudes are unprecedented in the past 600 years.”

Tingley and Huybers’ analysis shows, moreover, that these recent extremes are best explained by an overall rise in average temperatures. That is right in line with an overwhelming body of evidence showing that man-made greenhouse gas emissions have already driven global temperatures higher, and will continue to do so as the century progresses.

Rapid Arctic climate change has resulted in a stunning decline in Arctic sea ice cover, with 2012 setting the record for the lowest ice extent since satellite observations began in 1979. The plunge in sea ice is helping to boost temperatures by exposing greater areas of dark, open ocean, which absorbs more incoming solar radiation that the brightly colored ice does.

Related Content:
NOAA: 2012 Hottest & 2nd-Most Extreme Year On Record 
Climate to Warm Beyond Levels Seen for 11,300 Years
A Closer Look at Arctic Sea Ice Melt and Extreme Weather
The Story Behind Record Ice Loss in Greenland
Timelines in Timber: Inside a Tree-Ring Laboratory
It's Official: Arctic Sea Ice Shatters Record Low


By John Watson (New Bern, NC)
on April 12th, 2013

600 years ago? So right before the start of “The Little Ice Age” that we already knew we’d been warming from since 1850? Interesting…..this study tells us little or nothing new….

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By Paul Felix Schott (Barrington, Illinois 60010)
on April 13th, 2013

Scientist spotlight the world’s ice and how fast it is going. Scientist Giles and others have
noted through their studies most all ice on earth will be gone in the summers in the very
near coming years 10 to 20 the most. In many places on Earth the Ice that once was thousands of feet thick year round.

Scientist Dr. Katharine Giles was killed in a cycling collision in Victoria, London.
She is the second person from her UCL department to die in an so called accident.

Her death comes just three months after a senior colleague,
Prof Seymour Laxon, 49, died in a fall, hitting his head and suffering a
brain hemorrhage.

Scientist Dr. Giles had done many experiments investigating “Sea Ice Thickness”,
and showed to governments around the earth how the Sun rays and winds affected the newly exposed Arctic Ocean.
Scientist Dr. Giles to all Warning Water will warm faster then ICE.

Dr. Giles and many other Scientist from around the Globe have been looking at Photos of before and after of the ice at the polls and Glaciers. Glacier Bay Alaska is a 60+ miles long fjord that once was a Glacier that was from Sea Level to top was over a thousand feet thick and over 60 miles long, gone for ever.

Scotland Yard’s report said the accident took place at the junction of
Palace Street and Victoria Street, near Victoria Station, at 8.25am on Monday.

Scientist Giles, from west London, was pronounced dead at the scene. The male driver of
the HGV lorry stopped at the scene. He was not arrested.

Any witnesses to this crime or INFO on it are asked to call the Road Death Investigation Unit at Catford, South-East London on  
020 8285 1574. or Email it to many News Networks. Do both would be better.

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By Bob Bingham (Kerikeri)
on April 14th, 2013

Jennifer Francis of Rutgers U has done some stunning work on the relation between the Arctic ice loss and the extreme weather in the Northern hemisphere which shows that major disruptions to the climate have already started. We in the Southern hemisphere are keeping a close watch on the Antarctic which hold much more land based ice and would have a greater effect on sea levels.

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By Mike Lemonick (Princeton, NJ 08542)
on April 14th, 2013

Yes, Jennifer Francis has been a pioneer on this.

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By Clyde Israel (South Africa )
on April 15th, 2013

Please explain the following:
It contradicts your article and as an environmental student I am trying to make sense of it.

Reply to this comment

By Mike Lemonick (Princeton, NJ 08540)
on April 15th, 2013

Clyde Israel, I’m not sure how a story about ice cover in the winter can possibly contradict a story about Arctic summer heat.

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By Witkh13 (Spokane, Wa 99201)
on April 16th, 2013

Too bad you types who chose to believe the sky is falling are notorious liars: .  Let me know when you start doing real science instead of this regurgitated fiction.

Failed science is why it is bad to depend on personal blogs for your news.

Reply to this comment

By Atheist Dingle (Burnley, UK)
on July 31st, 2013

Witkh13, you can’t criticise people for citing personal blogs as sources of information and then link us to two Op Ed pieces which are basically personal blog posts but written for mainstream media publications.
And you especially can’t expect to be taken seriously when one of them is by James Delingpole.

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