Posted on 02/03/2012 9:32:32 AM PST by null and void
A new study appears to answer contentious questions about the onset and cause of Earth’s Little Ice Age, a period of cooling temperatures that began after the Middle Ages and lasted into the late 19th century.
According to the new study, the Little Ice Age began abruptly between A.D. 1275 and 1300, triggered by repeated, explosive volcanism and sustained by a self-perpetuating sea ice-ocean feedback system in the North Atlantic Ocean, according to University of Colorado Boulder Professor Gifford Miller, who led the study. The primary evidence comes from radiocarbon dates from dead vegetation emerging from rapidly melting icecaps on Baffin Island in the Canadian Arctic, combined with ice and sediment core data from the poles and Iceland and from sea ice climate model simulations, said Miller.
While scientific estimates regarding the onset of the Little Ice Age range from the 13th century to the 16th century, there is little consensus, said Miller. There is evidence the Little Ice Age affected places as far away as South America and China, although it was particularly evident in northern Europe. Advancing glaciers in mountain valleys destroyed towns, and famous paintings from the period depict people ice skating on the Thames River in London and canals in the Netherlands, waterways that were ice-free in winter before and after the Little Ice Age.
“The dominant way scientists have defined the Little Ice Age is by the expansion of big valley glaciers in the Alps and in Norway,” said Miller. “But, the time it took for European glaciers to advance far enough to demolish villages would have been long after the onset of the cold period,” said Miller, a fellow at CU’s Institute of Arctic and Alpine Research.
Most scientists think the Little Ice Age was caused either by decreased summer solar radiation, erupting volcanoes that cooled the planet by ejecting shiny aerosol particles that reflected sunlight back into space, or a combination of both, said Miller.
The new study suggests that the onset of the Little Ice Age was caused by an unusual, 50-year-long episode of four massive tropical volcanic eruptions. Climate models used in the new study showed that the persistence of cold summers following the eruptions is best explained by a sea ice-ocean feedback system originating in the North Atlantic Ocean.
“This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age,” said Miller. “We also have provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time. If the climate system is hit again and again by cold conditions over a relatively short period — in this case, from volcanic eruptions — there appears to be a cumulative cooling effect.”
A paper on the subject is being published January 31, 2012, in Geophysical Research Letters, a publication of the American Geophysical Union. The paper was authored by scientists and students from CU-Boulder, the National Center for Atmospheric Research in Boulder, the University of Iceland, the University of California, Irvine, and the University of Edinburgh in Scotland. The study was funded in part by the National Science Foundation and the Icelandic Science Foundation.
As part of the study, Miller and his colleagues radiocarbon-dated roughly 150 samples of dead plant material with roots intact collected from beneath receding ice margins of ice caps on Baffin Island. There was a large cluster of “kill dates” between A.D. 1275 and 1300, indicating the plants had been frozen and engulfed by ice during a relatively sudden event.
Both low-lying and higher altitude plants all died at roughly the same time, indicating the onset of the Little Ice Age on Baffin Island — the fifth largest island in the world — was abrupt. The team saw a second spike in plant kill dates at about A.D. 1450, indicating the quick onset of a second major cooling event.
To broaden the study, the team analyzed sediment cores from a glacial lake linked to the 367-square-mile Langjökull ice cap in the central highlands of Iceland that reaches nearly a mile high. The annual layers in the cores — which can be reliably dated by using tephra deposits from known historic volcanic eruptions on Iceland going back more than 1,000 years — suddenly became thicker in the late 13th century and again in the 15th century due to increased erosion caused by the expansion of the ice cap as the climate cooled, he said.
“That showed us the signal we got from Baffin Island was not just a local signal, it was a North Atlantic signal,” said Miller. “This gave us a great deal more confidence that there was a major perturbation to the Northern Hemisphere climate near the end of the 13th century.” Average summer temperatures in the Northern Hemisphere did not return to those of the Middle Ages until the 20th century, and the temperatures of the Middle Ages are now exceeded in many areas, he said.
The team used the NCAR-based Community Climate System Model to test the effects of volcanic cooling on Arctic sea ice extent and mass. The model, which simulated various sea ice conditions from about A.D. 1150-1700, showed several large, closely spaced eruptions could have cooled the Northern Hemisphere enough to trigger Arctic sea ice growth.
The models showed sustained cooling from volcanoes would have sent some of the expanding Arctic sea ice down along the eastern coast of Greenland until it eventually melted in the North Atlantic. Since sea ice contains almost no salt, when it melted the surface water became less dense, preventing it from mixing with deeper North Atlantic water. This weakened heat transport back to the Arctic and creating a self-sustaining feedback system on the sea ice long after the effects of the volcanic aerosols subsided, he said.
"Our simulations showed that the volcanic eruptions may have had a profound cooling effect,” says NCAR scientist Bette Otto-Bliesner, a co-author of the study. “The eruptions could have triggered a chain reaction, affecting sea ice and ocean currents in a way that lowered temperatures for centuries."
The researchers set the solar radiation at a constant level in the climate models, and Miller said the Little Ice Age likely would have occurred without decreased summer solar radiation at the time. “Estimates of the sun’s variability over time are getting smaller, it’s now thought by some scientists to have varied little more in the last millennia than during a standard 11-year solar cycle,” he said.
One of the primary questions pertaining to the Little Ice Age is how unusual the warming of Earth is today, he said. A previous study led by Miller in 2008 on Baffin Island indicated temperatures today are the warmest in at least 2,000 years.
Other co-authors on the paper include CU-Boulder's Yafang Zhong, Darren Larsen, Kurt Refsnider, Scott Lehman and Chance Anderson, NCAR's Marika Holland and David Bailey, the University of Iceland's Áslaug Geirsdóttir, Helgi Bjornsson and Darren Larsen, UC-Irvine's John Southon and the University of Edinburgh's Thorvaldur Thordarson. Larsen is doctoral student jointly at CU-Boulder and the University of Iceland.
GGG ping worthy?
> Medieval SUVs...
Do you mean Clydesdale horses?
They’d certainly be bigger than the average horse.
Which is absolute crap. The Chineese have been recording sunspots for a thousand years. Persian and Indian astronomers also have records going back hundreds of years. And there was a long dry spell called the Maunder minimum. It lasted from 1645 to 1715.
So called 'climate scientists' are outright liars.
/johnny
I was wondering if these guys were trying to take the position that the documented drop in solar activity during the Maunder Minimum had no effect on earth’s climate...
They also have a far large throughput, including gaseous emissions.
They also have a far large throughput, including gaseous emissions.
If the earth has not been this warm for 2,000 and the mini ice age came in between it does not take a rocket science to figure out global tempertures rise and fall naturally. I tend now not to believe anything from the climate science computer geeks that receive grant money to make climate computer projections. It’s to tempting to do the grantors bidding to keep one’s job. In 2012 after obama’s defeat we should make sure we go after the grant fraud, EPA fraud that the socialist democrats commited in funding these phoney studies.
It’s important (to progressives/liberals) to peg the cause of the little ice age on volcanic emissions rather than solar radiation because AGW cannot be supported otherwise.
At first the alarmists tried to ignore both the little ice age and the medieval warm period that came before it. That didn't work too well for them. Now they are coming up with other explanations that downplay the sun's role and emphasize air pollution’s role. To them a volcano IS mother nature's equivalent to SUV’s.
If you will notice this “theory” is once again based largely on computer models that they manipulated to get the results they wanted. The article starts off with, “the Little Ice Age began abruptly between A.D. 1275 and 1300, triggered by repeated, explosive volcanism and sustained by a self-perpetuating sea ice-ocean feedback system”. Then they get a little more specific, “the Little Ice Age was caused by an unusual, 50-year-long episode of four massive tropical volcanic eruptions.” Never mind that the previous statement said that the Little Ice Age began abruptly between A.D. 1275 and 1300 which is a 25 year period.
Then we learn that, “This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age,”. Umm, yeah right... I guess if you ignore textbooks written fifty years ago that might be true. Since they claim to be the first, I would like to know exactly which “four massive tropical volcanic eruptions” triggered The Little Ice Age.
Of course it gets back to, “Our simulations showed that the volcanic eruptions may have had a profound cooling effect”. I think that most people are aware that volcanic dust in the atmosphere does appear to have a cooling effect on the climate, however it is generally thought that this effect is short-lived because the excess dust generally settles out within a year or two at most. If you ignore the effects of gravity and precipitation in your computer models I suppose that this phenomena could be drawn out far longer than that.
“The team used the NCAR-based Community Climate System Model to test the effects of volcanic cooling on Arctic sea ice extent and mass.” I would be curious if the physical evidence for the massiveness and timing of the four tropical volcanoes is in the historical record or if the evidence is derived from the study’s own computer models. Given the past actions of these particular researchers I would guess that physical observations and evidence played a far smaller role than did the reliance on the all-knowing computer model.
“Then they get a little more specific, “the Little Ice Age was caused by an unusual, 50-year-long episode of four massive tropical volcanic eruptions.”
I wonder where the massive eruptions were. All in Iceland?
All in tropical Iceland...
1150 A.D. - Quilotoa, Ecuador Erupts; Volcanic Explosivity Index (VEI) = 6
1150 A.D. Little Ice Age (First Peak) Begins
1259 A.D. - Very large eruption, Origin Unknown. Twice the size of the Mt.Tambora eruption in 1815 A.D. - this would make a Volcanic Explosivity Index (VEI) = 8 or more; possibly qualifying as a Super Volcanic Eruption.
Antarctica ice core data; Norwegian tree rings; England and Europe - numerous references to dark skies and unseasonable cold, one obscure reference to pillar of fire in western sky; Chinese reference to pillar of fire in southern sky; Indonesian description - near Krakatau - magma rose in a miles wide column into the troposphere lasting for some days before subsiding, according to refferences.
1452 A.D. - Kuwae, Vanuatu, New Hebrides Arc Erupts; Volcanic Explosivity Index (VEI) = 6.
1460 A.D. - Little Ice Age (First Peak) Ends
See my post 15
I witnessed the Mt. St Helen's eruption; it looked pretty massive to me. Which four “massive” tropical volcanoes which took place in a 50 year period that supposedly triggered the little ice age are they referring to in the study? Are they referring to actual events or events that they believe happened because of their simulation results? The article does not make it clear and it certainly makes no reference to the three events you mention that were spread over a 300 year period not a "50 year" period.
ping
Yours is based on historical events not computer modeled events.
—
Don’t’cha just hate it when historical events contradict the reality of computer models?
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