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Arctic warming overtakes 2,000 years of natural cooling

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September 6, 2009

The blue line shows estimates of Arctic temperatures over the last 2,000 years. The green ...

The blue line shows estimates of Arctic temperatures over the last 2,000 years. The green line shows the long-term cooling trend. The red line shows the recent warming based on actual observations. (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.

The scientists reconstructed summer temperatures across the Arctic 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 climate change," 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."

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.

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.

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.

This 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.

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 Climate System 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 temperature 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."

The research was primarily funded by the National Science Foundation, NCAR's sponsor.

7 Comments

This article is an example why we on the "non-believers" side won. Take a look at the current daily observed Polar Ice chart:

http://www.ijis.iarc.uaf.edu/seaice/extent/AMSRE_Sea_Ice_Extent.png

Feel free to check on the source, the International Arctic Research Center. Again, this is not a computer model, but the actual satellite-observed polar icepacks. It updates daily. And as you can see the polar ice levels are exactly the same today as they were ten years ago.

Why the difference with the huge spike shown in this article? Well, like almost all global wamring publications, the actual data are not shown. However, lengthy descriptions of the process by which the conclusions were "simulated", "inferred" and "reconstructed" are expected to suffice for those of us who don't demand more from science.

For anyone interested in this debate, use traditional science and start from the bottom up. Use raw, observed sources of data that are not "modeled" or "projected", and draw your own conclusions.

Todd Dunning
7th September, 2009 @ 04:09 pm PDT

G'day, even if the climate warms, which it ain't, this can only be good for people. Paleohistory (?) has shown that during warming periods (interglacials) humans thrived due to an abundance of food and limited exposure to freezing weather. The glacial periods are the most dangerous to humans, having reduced the population significantly each time. The most recent evidence of this is the medieval warming where populations grew and the mini ice age (mid 1600's -1800's) which was a very harsh and deadly period. The warming period we have recently experienced was a result of coming out of the mini ice age. The rise in CO2 concentrations is a result of that warming.

Of course, Mann et al choose to totally ignore the medieval Warming and the Mini Ice Age so they could come up with their "Hockey Stick". Besides, given that the IPCC is a political body, the data used in "The Models" is manipulated if not erroneous or an outright lie.

If anthropological CO2 emissions are the cause of Global Warming and humans are pumping more and more of this harmless gas into the atmosphere, why has the global temperature actually fallen by 0.75% since 1998?

If you wish to get a better idea of what the climate will do, check out the sunspot activity, the Jupiter Effect, the Earth's orbit and the Earth's axial tilt.

The Old Farmers Almanac is quite accurate in its prediction as are many long range forecasters. They understand history.

rrvau
9th September, 2009 @ 03:26 am PDT

I can see that people are not buying into this propaganda. The whole idea of man caused global warming is being proven to be a big scam. Haven't you people heard of "Climategate"? Global temperatures have been fraudulently altered. Freedom of Information requests were ignored. The raw temperature date has been conveniently "lost". Wake up to the blatant and obvious fraud!

Watch "The Great Global Warming Swindle" here. Mind you, this came out before all the "Climategate" scandal, and still does a great job of ripping apart the anthropogenic global warming theory. http://vids.myspace.com/index.cfm?fuseaction=vids.individual&videoid=51808636

Rudy B
4th March, 2010 @ 07:36 pm PST

Reading these comments now is pretty funny. According to NASA this has been the warmest 12 months in their 130 year record. The Arctic sea ice melt this summer was close to record breaking and the Arctic now is very warm for this time of year. The latest research suggests that cloud cover changes will amplify rather than moderate global warming - although there are still much certainty in cloud feedback.

rrvau theories are beyond stupid. What matters to the stability of human civilization is not the global average temperature, but the rate at which it changes. We have never been through anything like this rate of increase. Further, likely the worst part of climate change is the increase in droughts. Higher temps mean the amount of water in soil will decrease as more of it will be in vapor form. Net global plant production, which at first rose in response to higher CO2, has now started to decrease do to less H2O.

And then there is the impact on the oceans. Warming is killing coral reefs and phytoplankton has dropped 40% since 1950 do to warming slowing ocean turnover. And then there is ocean acidification.

That best way to promote energy conversation and the development of alternative energy production (solar, wind, biofuels, nuclear and maybe CO2 sequestering) is to put a price on GHG emissions - by a tax or cap and trade - and then reduce other taxes or have an annual energy rebate. Tax carbon not income!

Mike435
12th December, 2010 @ 03:39 pm PST

Todd Dunning,

I'm not sure what crazy filter you are viewing that article you posted through but it clearly shows two things: 1) The Arctic summer ice level hit an all time low in 2012 and 2) the ice level is becoming increasingly more unstable (ie larger difference in level between summer and winter.) Your very article that you say denies climate change actually shows drastic changes are taking place. Similarily, if you follow the data to the full source, http://kuroshio.eorc.jaxa.jp/JASMES/climate/data/graph/JASMES_CLIMATE_SIE_197811_201212_5DAVG_ES_NHM_100.png you will see an overall trend of less ice each year. So... yea...

Empathetic
2nd November, 2012 @ 03:49 pm PDT

Meanwhile most Antarctic temperatures since 1958 are the inverse of the Arctic Hockey Stick chart shown

http://www.unis.no/35_staff/staff_webpages/geology/ole_humlum/AntarcticTemperatureChanges.htm

Ice thickness gains around Antarctica, mostly on the continental shelf

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120013495_2012013235.pdf

I have more to fear of the Earth crust displacement due to the massive shift of mass to the Antarctic, ending the Earths seasons.

other links.

http://www.real-science.com/arctic-meltdown

Weirder still is the alteration of data:

http://notrickszone.com/2012/04/13/hansen-shocks-adjusts-antarctica-temperatures-changes-warming-trend-to-cooling/

L1ma
20th December, 2012 @ 10:24 am PST

The green line showing the mean (average?) the trend conveniently stops once the warming began. Note that the blue line (temperature change as a result of axis tilt, not greenhouse gasses) abruptly shoots up (coincidentally) at the start of the industrial revolution. Why not plot that green line up until today...its slope would be in line with measured temps. Noone is arguing that greenhouse gases dont warm the atmosphere, but the degree of its impact vs cosmological factors appears to be exagerated as evidenced by this data.

JBar
14th February, 2013 @ 04:31 am PST
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