Long-term Cooling Trend In Arctic Abruptly Reverses

gerky

ScienceDaily wrote:

Long-term Cooling Trend In Arctic Abruptly Reverses, Signaling Potential For Sea Rise
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Researchers secure a floating platform used to take sediment cores from Sunday Lake in southwestern Alaska. Sediment generated by the small cirque glacier is carried to the lake by meltwater. The amount of sediment delivered to the lake can vary with the intensity of the summer melt season. (Credit: Darrell Kaufman, Northern Arizona University)

ScienceDaily (Sep. 3, 2009) — Warming from greenhouse gases has trumped the Arctic's millennia-long natural cooling cycle, suggests new research. Although the Arctic has been receiving less energy from the summer sun for the past 8,000 years, Arctic summer temperatures began climbing in 1900 and accelerated after 1950.

The decade from 1999 to 2008 was the warmest in the Arctic in two millennia, scientists report in the journal Science. Arctic temperatures are now 2.2 degrees F (1.2 degrees C) warmer than in 1900.

To track Arctic temperatures 2,000 years into the past, the research team analyzed natural signals recorded in lake sediments, tree rings and ice cores. The natural archives are so detailed the team was able to reconstruct past Arctic temperatures decade by decade.

As part of a 21,000-year cycle, the Arctic has been getting progressively less summertime energy from the sun for the last 8,000 years. That decline won't reverse for another 4,000 years.

The new research shows the Arctic was cooling from A.D. 1 until 1900, as expected. However, the Arctic began warming around 1900, according to both the natural archives and the instrumental records.

"The amount of energy we're getting from the sun in the 20th century continued to go down, but the temperature went up higher than anything we've seen in the last 2,000 years," said team member Nicholas P. McKay of The University of Arizona in Tucson.

"The 20th century is the first century for which how much energy we're getting from the sun is no longer the most important thing governing the temperature of the Arctic," said McKay, a UA doctoral candidate in geosciences.

Greenhouse gases are the most likely cause of the recent rise in Arctic temperatures, said McKay and his co-author Jonathan T. Overpeck, a UA professor of geosciences and director of UA's Institute of the Environment.

Overpeck said, "The Arctic should be very sensitive to human-caused climate change, and our results suggest that indeed it is."

As the Arctic warms, the warming accelerates, he said, because there is less snow and ice to reflect solar energy back into space. Instead, the newly exposed dark soil and dark ocean surfaces absorb solar energy and warm further.

McKay, Overpeck, lead author Darrell S. Kaufman of Northern Arizona University in Flagstaff and their colleagues will publish their findings in the September 4 issue of Science. The National Science Foundation funded the research.

Overpeck and his colleagues have been working in the Arctic for about 20 years to understand the region's ancient climate. Until recently, the group had been able to peer back in time only 400 years.

About five years ago, Kaufman, Overpeck and their colleagues began a multi-institution project to analyze sediment cores from more than two dozen Arctic lakes. Lake sediments are often laid down in distinct yearly layers, much like the rings of a tree.

As part of the research for his master's degree at NAU, McKay collected and analyzed sediment cores from Hallet Lake in south-central Alaska.

The annual sediment layers contain indicators of temperature and climate. The changes in the abundance of algae remnants reflect the length of the growing season. In addition, warmer summers result in a thicker annual sediment layer because as glacial meltwater increases, more sediment is deposited.

For the new climate reconstruction, the researchers compared the information from lake sediments with previously published climate reconstructions of the Arctic based on glacial ice cores and tree rings. The data from the natural archives were calibrated against the instrumental temperature record.

The analysis shows that summer temperatures in the Arctic, in step with reduced energy from the sun, cooled at an average rate of about 0.36 degrees F (0.2 degrees C) per thousand years -- until the 20th century.

"The data tell a remarkably clear and consistent story," McKay said.

The scientists also compared their new work with climate reconstructions from a computer model of global climate based at the National Center for Atmospheric Research (NCAR) in Boulder, Colo.

The model's estimate of the reduction of seasonal sunlight in the Arctic and the resulting cooling was consistent with the analysis from natural archives. The finding gives scientists more confidence in computer projections of future Arctic temperatures.

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.

The finding has implications far beyond the Arctic, McKay and Overpeck said.

Warming in the Arctic may affect sea level rise, primarily from the melting of the great ice sheets, Overpeck said.

A warming Arctic affects weather in the southwestern U.S., McKay said. "Winter storms in the western U.S. are going further north than they used to -- and these are the same storms that bring our rain and snowfall."

Kaufman, McKay and Overpeck's co-authors on the paper, "Recent Warming Reverses Long-Term Arctic Cooling," are David P. Schneider, Caspar M. Ammann and Bette L. Otto-Bliesner of NCAR in Boulder, Colo.; Raymond S. Bradley of the University of Massachusetts, Amherst; Keith R. Briffa of the University of East Anglia in Norwich, UK; Gifford H. Miller of the University of Colorado in Boulder; Bo M. Vinther of the University of Copenhagen in Denmark; and the NSF Arctic System Science Program in Fairbanks, Alaska.

Journal reference:

1. Darrell S. Kaufman, David P. Schneider, Nicholas P. McKay, Caspar M. Ammann, Raymond S. Bradley, Keith R. Briffa, Gifford H. Miller, Bette L. Otto-Bliesner, Jonathan T. Overpeck, Bo M. Vinther, and Arctic Lakes 2k Project Members. Recent Warming Reverses Long-Term Arctic Cooling. Science, 2009; DOI: 10.1126/science.1173983

Adapted from materials provided by University of Arizona. Original article written by Mari N. Jensen, UA College of Science.

http://www.sciencedaily.com/releases/2009/09/090903163721.htm
http://news.nationalgeographic.com/news/2009/09/090903-arctic-warming-ice-age.html
http://news.bbc.co.uk/2/hi/science/nature/8236797.stm

I know this is a long article but its quite interesting and following on from previous research.

Shiny

Is Dublin vulnerable to a significant rise in sea levels?

Jim Martin

Shiny wrote: »

Is Dublin vulnerable to a significant rise in sea levels?

Looks pretty bad with a 7m sea level rise:

http://flood.firetree.net/

derry

Yet more CO2 tripe
If as they say suddenly in 1900 the downward trend in temperature for the last 8000 years reversed, there is the problem that the CO2 rises in 1900 were not significant and most C02 rises were not until 1950 onwards.
This largely decouples for me the CO2 link to this local regional temperature rise

Yes there might be a rising temp in this local region of the arctic and the link to CO2 is assumed like the fashion in science is to blame everything on CO2 .
Then even if the ice melts in the arctic it wont impact the sea level much as the ice sheet floats on the sea so sea levels are not impacted much. The remaining glaciers in Norway Greenland Alaska are not enough ice on land to change sea levels much.
To change sea levels a lot requires the melting of the Antarctic which is Ice on land. Its assumed it would take hundreds probably thousands of years to melt the Antarctic ice even if temperatures increased.Certianlymakes the greenpeace lie the artic will be ice free in thirty years a real laugh in science circles

The science world knows much to thier annoyance wher they got cuaght out asleep at the wheel for decades that global dimming has existed for quite some time .That's where partials which enter the atmosphere from burning coal and volcanic activity can reduce the amount of sunlight hitting the earth. Also these suspended particles tend to be the color black and when they settle on the snow can help melt snow faster. Since the 1980,s there has been a big reduction in partials existing coal burning stations due to scrubbers etc. So we can start to expect to see less snow melted from global dimming

That's not to say these partials are the source of the temperature rise in this local region of the Arctic Alaska. Merely to show the complexity of the dynamic systems of the planet means that choosing CO2 as the offender is much the same as choosing thee fact that hem lines in dresses went upwards since 1900 made the arctic heat up.

As usual another CO2 boogieman paper made in obscure Alaska without comparing it to how it fits to other regions like Norway or Russia or Greenland were the exact opposite might be happening.


Anyway the real bad news was the fact the sun rays hitting the earth are less for the next 4000 years means we are gonna go into a colder planet with less food production and less natural activity and that is definitely real bad news.

I think the increase in polar bears population in this local region Alaska and their flatulace or farts is the source of the problem and a dammed good culling of polar bears will sort the problem


Derry

djpbarry

derry wrote: »

If as they say suddenly in 1900 the downward trend in temperature for the last 8000 years reversed, there is the problem that the CO2 rises in 1900 were not significant...

Define “significant”.

derry wrote: »

Yes there might be a rising temp in this local region of the arctic and the link to CO2 is assumed like the fashion in science is to blame everything on CO2 .

I think it’s fair to say it’s a little more than an “assumption” or "fashion". There is a sound physical basis for the anthropogenic global warming theory.

derry wrote: »

To change sea levels a lot requires the melting of the Antarctic which is Ice on land. Its assumed it would take hundreds probably thousands of years to melt the Antarctic ice even if temperatures increased.

Source?

derry wrote: »

The science world knows much to thier annoyance wher they got cuaght out asleep at the wheel for decades that global dimming has existed for quite some time .

I’m not sure what this is supposed to mean; global dimming was not known to exist until it was discovered? By scientists, no doubt.

derry wrote: »

Merely to show the complexity of the dynamic systems of the planet means that choosing CO2 as the offender is much the same as choosing thee fact that hem lines in dresses went upwards since 1900 made the arctic heat up.

The obvious difference being that there is no physical connection (of which I am aware) between hemlines and the arctic climate.

derry wrote: »

As usual another CO2 boogieman paper made in obscure Alaska without comparing it to how it fits to other regions like Norway or Russia or Greenland were the exact opposite might be happening.

Perhaps you could take a look at the original paper and tell us where the authors have gone wrong? What have they failed to take into consideration?

Why would we want anything but a halt to arctic cooling?
Doesnt make sense to want it to get cooler.

All it took was a 1c drop in average temps to cause the little ice age and famine in Europe!

The Great Famine of 1315-1317 killing 1.5 million people alone
The IPCC describes the LIA as a modest cooling of the Northern Hemisphere during this period of less than 1°C.

http://www.economicexpert.com/a/Little:Ice:Age.htm