Arctic at warmest levels in 2,000 years or more

Sep 03, 2009
New research shows that the Arctic reversed a long-term cooling trend and began warming rapidly in recent decades. The blue line shows estimates of Arctic temperatures over the last 2,000 years, based on proxy records from lake sediments, ice cores and tree rings. The green line shows the long-term cooling trend. The red line shows the recent warming based on actual observations. A 2000-year transient climate simulation with NCAR’s Community Climate System Model shows the same overall temperature decrease as does the proxy temperature reconstruction, which gives scientists confidence that their estimates are accurate. Credit: Courtesy Science, modified by UCAR.

Arctic temperatures in the 1990s reached their warmest level of any decade in at least 2,000 years, new research indicates. The study, which incorporates geologic records and computer simulations, provides new evidence that the Arctic would be cooling if not for greenhouse gas emissions that are overpowering natural climate patterns.

The international study, led by Northern Arizona University and the National Center for Atmospheric Research (NCAR), will be published in the September 4 edition of Science. It was primarily funded by the National Science Foundation, NCAR's sponsor.

The scientists reconstructed summer temperatures across the over the last 2,000 years by decade, extending a view of climate far beyond the 400 years of Arctic-wide records previously available at that level of detail. They found that thousands of years of gradual Arctic cooling, related to natural changes in Earth's orbit, would continue today if not for emissions of carbon dioxide and other greenhouse gases.

"This result is particularly important because the Arctic, perhaps more than any other region on Earth, is facing dramatic impacts from ," says NCAR scientist David Schneider, one of the co-authors. "This study provides us with a long-term record that reveals how greenhouse gases from human activities are overwhelming the Arctic's natural climate system."

Darrell Kaufman of Northern Arizona University, the lead author and head of the synthesis project, says the results indicate that recent warming is more anomalous than previously documented.

"Scientists have known for a while that the current period of warming was preceded by a long-term cooling trend," says Kaufman. "But our reconstruction quantifies the cooling with greater certainty than before."

Greenhouse gases overtake a natural cycle

The new study is the first to quantify a pervasive cooling across the Arctic on a decade-by-decade basis that is related to an approximately 21,000-year cyclical wobble in Earth's tilt relative to the Sun. Over the last 7,000 years, the timing of Earth's closest pass by the Sun has shifted from September to January. This has gradually reduced the intensity of sunlight reaching the Arctic in summertime, when Earth is farther from the Sun.

An illustration showing an abrupt reversal in Arctic cooling despite an increasing distance between the sun and Earth during the Arctic summer solstice. Credit: National Science Foundation

The research team's temperature analysis shows that summer temperatures in the Arctic, in step with the reduced energy from the Sun, cooled at an average rate of about 0.2 degrees Celsius (about .36 degrees Fahrenheit) per thousand years. The temperatures eventually bottomed out during the "Little Ice Age," a period of widespread cooling that lasted roughly from the 16th to the mid-19th centuries.

Even though the orbital cycle that produced the cooling continued, it was overwhelmed in the 20th century by human-induced warming. The result was summer temperatures in the Arctic by the year 2000 that were about 1.4 degrees C (2.5 degrees F) higher than would have been expected from the continued cyclical cooling alone.

"If it hadn't been for the increase in human-produced greenhouse gases, summer temperatures in the Arctic should have cooled gradually over the last century," says Bette Otto-Bliesner, an NCAR scientist who participated in the study.

Natural archives of Arctic climate

To reconstruct Arctic temperatures over the last 2,000 years, the study team incorporated three types of field-based data, each of which captured the response of a different component of the Arctic's climate system to changes in temperature.

These data included temperature reconstructions published by the study team earlier this year. The reconstructions were based on evidence provided by sediments from Arctic lakes, which yielded two kinds of clues: changes in the abundance of silica remnants left behind by algae, which reflect the length of the growing season, and the thickness of annually deposited sediment layers, which increases during warmer summers as deposits from glacial meltwater increase.

To collect sediment samples from lakes in Alaska, NAU researchers often travel by floatplanes and spend days working from a floating platform, using hand-operated weights to tap collection tubes upward of 20 feet into the lake bottom, such as this one at Sunday Lake. Credit: Northern Arizona University

The research also incorporated previously published data from glacial ice and tree rings that were calibrated against the instrumental temperature record.

The scientists compared the temperatures inferred from the field-based data with simulations run with the Community Model, a computer model of global climate based at NCAR. The model's estimate of the reduction of seasonal sunlight in the Arctic and the resulting cooling was consistent with the analysis of the lake sediments and other natural archives. These results give scientists more confidence in computer projections of future Arctic temperatures.

"This study provides a clear example of how increased greenhouse gases are now changing our climate, ending at least 2,000 years of Arctic cooling," says NCAR scientist Caspar Ammann, a co-author.

The new study follows previous work showing that temperatures over the last century warmed almost three times faster in the Arctic than elsewhere in the Northern Hemisphere. This phenomenon, called Arctic amplification, occurs as highly reflective Arctic ice and snow melt away, allowing dark land and exposed ocean to absorb more sunlight.

"Because we know that the processes responsible for past Arctic amplification are still operating, we can anticipate that it will continue into the next century," says Gifford Miller of the University of Colorado at Boulder, a member of the study team. "Consequently, Arctic warming will continue to exceed increases in the rest of the Northern Hemisphere, resulting in accelerated loss of land ice and an increased rate of sea level rise, with global consequences."

More information: "Recent Warming Reverses Long-Term Arctic Cooling", Published in journal Science on Sep 4.

Source: University of Colorado

Explore further: 2014 Arctic sea ice minimum sixth lowest on record (Update)

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User comments : 25

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x646d63
3.6 / 5 (9) Sep 03, 2009
And what about the last ten years?
jonnyboy
3 / 5 (10) Sep 03, 2009
The problem with this research is that we have no idea whether or not this particular group of researchers is using real data or manipulated date like the so called "hockey stick" of global warming.
Soylent
2.6 / 5 (5) Sep 03, 2009
And what about the last ten years?


What about them?

http://en.wikiped...cord.png
x646d63
3.3 / 5 (7) Sep 03, 2009
@Soylent: your link isn't relevant. This article is about the Arctic and only the Arctic. Your link is the global instrumental temperature record.

As we know, 2000 (the last year they provide data for) was the peak of increasing solar activity over the last 150 years. But things have been getting rather quiet over the last 10.

http://upload.wik...bfly.gif

No data for 2001-2009 is suspicious to me.
mhouck
2.1 / 5 (7) Sep 03, 2009
or just look at nasa satellite photos, i believe ice melts when it gets warm???
mhouck
2.7 / 5 (12) Sep 03, 2009
conspiracists need to quit thinking everyone is out to get them, global warming is real and we have walked on the moon. dont let your mind be easily manipulated (pollution = negative side effects) simple as that.
Allaytros
1.9 / 5 (9) Sep 03, 2009
I figure everyone who doesn't believe global warming is conservative. As in, watches Glenn Beck, Rush Limbaugh, O'Reily and whatnot. I don't oppose this. How is a homogeny of thought useful? Dissenting ideas are valuable. If not for them, how would paradigm shifts happen? Granted it has already happened...
Soylent
2.6 / 5 (5) Sep 03, 2009
@Soylent: your link isn't relevant. This article is about the Arctic and only the Arctic.


What about it? I'm not trying to be dismissive, I'm trying to figure out what you're insinuating.

Surface air temperature anomaly for lattitude 60°-90°:

http://www.arctic...e/a1.jpg
WG681
3 / 5 (6) Sep 03, 2009
The Earth will take care of itself.
wes_george
3.5 / 5 (11) Sep 03, 2009
We know that it was warmer in the Arctic between circa 1000 to 1200 years BP than today because Viking colonists settled Greenland (Green land, get it?) and established successful dairy farms where only glaciers grow today. They even exported cheese to Europe! Furthermore there are Norse graveyards in Greenland under six feet of permafrost. Obviously dug before today's permafrost existed.

Since Viking dairy farms in Greenland are an undisputed historical fact, ipso facto to claim that the Arctic is now warmer than at any time in the past 2,000 years is simply a false statement.
dionliddell
3.9 / 5 (11) Sep 04, 2009
Would it be safe to say that the Medieval Warm Period is An Inconvenient Truth? :-)
Velanarris
3.1 / 5 (7) Sep 04, 2009
I figure everyone who doesn't believe global warming is conservative. As in, watches Glenn Beck, Rush Limbaugh, O'Reily and whatnot. I don't oppose this. How is a homogeny of thought useful? Dissenting ideas are valuable. If not for them, how would paradigm shifts happen? Granted it has already happened...

I think all three of them are idiots and your stance on people's beliefs of global warming are incredibly off base. I think AGW is possible. I also believe it has absolutely nothing to do with CO2.

As an aside to this statement, it's pretty funny that all the crazy things that outspoken conservatives (read: outspoken, not Palin/O'Reilly style liers), have been saying about the government are starting to prove legit.

Just look at the Cyber Defense Act, in no uncertain terms it grants the President the authority to invade and shutdown private networks. That's insanity as well as illegal seizure and assault on the rights of free speech.

The MA Helath Safety Act allows the State Police to pull people out of their homes and send them to "quarantine camps" in times of medical crisis. Sounds an awful lot like a Concentration Camp to me.

Maybe you shouldn't generalize. After all, most liberal and progressive contention with the Republican party is due to the generalizations of the loonier among the right wing.
docknowledge
3.3 / 5 (3) Sep 04, 2009
What's hilarious (dependent on your sense of humor, of course), is that the main online San Francisco newspaper is currently running a poll about this article. Options are "Believable", "Irrelevant", and "At least it delays the next ice age".

And you won't believe how many people voted for the last choice....
otto1923
3 / 5 (4) Sep 04, 2009
conspiracists need to quit thinking everyone is out to get them, global warming is real
Yes, melting Arctic ice makes it easier to get at massive Arctic oil deposits shaken and stirred for more efficient extraction by recent subsurface nuclear detonations (peaceful applications). Providence- hand of God or hand of Man? Is there a difference?
otto1923
1 / 5 (3) Sep 04, 2009
At least it delays the next ice age
And if you're a Stonehenge whole-earther you might believe Gaia created the human race because she was tired of getting froze over every so often. You know- as bioengineered coal and oil metabolizers.
otto1923
2.3 / 5 (4) Sep 04, 2009
Maybe you shouldn't generalize. After all, most liberal and progressive contention with the Republican party is due to the generalizations of the loonier among the right wing
"There is a Time for democrats and a Time for republicans. There is a Time to scatter money and a Time to gather it up." -Its in the bible-
dachpyarvile
3.7 / 5 (6) Sep 05, 2009
It's a reincarnation of the hockey stick! AAAAAAAAAAAH!!!
Nartoon
3.3 / 5 (7) Sep 06, 2009
Whether AGW is real or not, cutting CO2 to 80% less than 1990 is suicide. Adaption allows us to continue our lifestyle and possibly improve those less fortunate in the third world. If we give up electricity they'll be 95% unemployment and the third world will die off from lack of donations. If we adapt we'll be able to expand our lifestyle to the third world and it'd still be 1/4 the cost of reduction.
Sirussinder
3.4 / 5 (5) Sep 06, 2009
Who cares, back in the 1970's people were afraid of an upcoming ice age.

Nothing but smoke and mirrors, Al Gore is hanging in his mansion with the eco-scum eating the fancy caviar flown in fresh from Russia right now.
tomliotta
3 / 5 (6) Sep 06, 2009
[We know that it was warmer in the Arctic between circa 1000 to 1200 years BP than today because Viking colonists settled Greenland (Green land, get it?) and established successful dairy farms where only glaciers grow today.]

No, we don't know that. Further, the presence of glaciers would make it very difficult to establish the historical sites of any dairy farms; so, an assertion that farms used to be where glaciers are today is ridiculous. Any archeological evidence wouldn't be found under glaciers. And further still, the glaciers of today are the result of an additional thousand years of cooling. No one knows precisely how much they've advanced during that time. However, they stand a good chance of retreating even faster.
wes_george
3.3 / 5 (7) Sep 06, 2009
Tomliotta,

Twisted my words. The archeological sites are not under glaciers. Vikings most certainly raised dairy cattle in Greenland. This is a historic fact, undisputed by anyone, but you, apparently.

Moreover, Norse colonies in Greenland were so successful that they product export quantities of cheese which they exported to Europe. How's that Greenland dairy industry going nowadays?

Jared Diamond describes how the Vikings were driven out of Greenland by climate change (colder) after several hundred years in his book "Collapse : How Societies Choose to Fail or Survive."

A hypothesis is only as good as its predictions. Kaufman, et al know that for the AGW hypothesis to not be false the data must show that the world is warmer now than in the past 2,000 years! It's not, unfortunately.

So to prove the world is warmer now they ignored inconvenient historical evidence as well as cherry picked the scientific proxy data that conforms to their personal bias for a very hot 20 th century.

Viking dairy farms in Greenland is one example that the AGW hypothesis cannot account for, but it is a fatal flaw since atmospheric CO2 level were much lower 1,000 years ago than today.

So, how to you explain that the Arctic was warmer 1,000 years ago than today?

Apparently, Kaufman doesn't. What he does is try to prove it was cooler then instead, even in the face of historical evidence. It's just bad science. The man has hurt his career. Sad, really.

Velanarris
5 / 5 (1) Sep 06, 2009
Whether AGW is real or not, cutting CO2 to 80% less than 1990 is suicide. Adaption allows us to continue our lifestyle and possibly improve those less fortunate in the third world. If we give up electricity they'll be 95% unemployment and the third world will die off from lack of donations. If we adapt we'll be able to expand our lifestyle to the third world and it'd still be 1/4 the cost of reduction.

This would also lead to a reduction in the population as we've proven that the "First World" lifestyle of equal education and industrialization leads to fewer children due to the abolishment of subsistence farming and large families to work the land. Less population always leads to greater stability and resource wealth. More resource wealth leads to productivity and educational prowess, which leads to greater resource wealth and energy efficiency.

Isn't that what the green movement is after anyway?
otto1923
5 / 5 (2) Sep 06, 2009
so, an assertion that farms used to be where glaciers are today is ridiculous
Interesting. I'm fairly new at this anonymous commentary thing, but I'm amazed at the freedom it gives to certain people to display how ignorant they are or too lazy to search google before brazenly exposing themselves. Seriously, aren't you embarrassed? I would have taken the opportunity to research what you're commenting on and learn something new instead of puking in public like you did. 

People shouldn't participate here if they are drunk, stoned, or irresponsibly brainless. 
otto1923
5 / 5 (2) Sep 06, 2009
Here, let me help you out:
http://www.morris...land.doc
-It appears that Greenland settlers fell due to a combination of factors including ruination of their own environment-
dachpyarvile
5 / 5 (3) Sep 06, 2009
[We know that it was warmer in the Arctic between circa 1000 to 1200 years BP than today because Viking colonists settled Greenland (Green land, get it?) and established successful dairy farms where only glaciers grow today.]

No, we don't know that. Further, the presence of glaciers would make it very difficult to establish the historical sites of any dairy farms; so, an assertion that farms used to be where glaciers are today is ridiculous. Any archeological evidence wouldn't be found under glaciers. And further still, the glaciers of today are the result of an additional thousand years of cooling. No one knows precisely how much they've advanced during that time. However, they stand a good chance of retreating even faster.


Ummm, no one is claiming that the archaeological evidence of warmer climate was under what is glacier but what is now permafrost. There is a difference and I would suggest that you take a little more time to understand the science rather than panicking about warming that is within parameters of the past.

Fact is, deep Viking graves have been found in what is now permafrost. This is scientifically documented. Roots of plants are found in what is now permafrost. That means that the climate was warmer by at least 2°C to 4°C 1000 years ago. Period.

According to other evidence, it was more like between 4°C to 5° higher.

See H. H. Lamb, Climate, History, and the Modern World, pp. 157-159.

See also Knud Frydendahl, "The summer Climate in the North Atlantic about the Year 1000" in Viking Voyages to North America, Birthe L. Clausen (Denmark: Kannike Tryk A/S, 1993), 90-94.

The latter source also can be read here:

http://www.canadi...7en.html