This is an important review of the Greenland ice core data. For some reason, and not the reason that I espouse today, in the early nineties, I saw fit to locate the raw ice core data and download it on my old 386. This was before browsers so that meant locating the appropriate bulletin board and getting the text file. Now you have to pay for it.
I was able to satisfy myself of the existence of a climate break about 12,900 years ago. I also realized that this was rapidly approaching the limits of data retention by the cores. Resolution was breaking down and becoming increasingly unreliable. That is worth remembering, though I anticipate that the number of cores has increased markedly and that is somewhat improving resolution.
We now have three apparently well defined climate breaks. The first at 14,700 years was a sharp global warming of around ten degrees or so that arrived over night and then fairly quickly reversed and disappeared restoring former conditions. This has been associated with a huge fresh water pulse out of the Antarctic, although I do not know how they know that. It does make sense that this was driven by events out of the Antarctic.
The second event 12,900 years ago we have already described as the Pleistocene Nonconformity, in which the crust shifted thirty degrees, placing the icecap out of the polar region. This obviously implied a climate shift that would be reflected as a precipitation change immediately upon the events occurrence. The ice core record shows just that and in fact we can split the record into before and after uniform precipitation averages. This shrouds the importance of the other two events and makes them easy to ignore as I did when I first reviewed the data.
The third event 11,700 years ago must coincide with the flushing of the monster lake Agassiz. This huge sea of melt water broke out and drained probably within a year, causing a worldwide coastal flooding event that may well be one of the sources of the cultural history of global floods.
It continues to amaze me how successful oral histories were able to transmit the gist of real events over thousands of years. You would expect natural skepticism and story telling insertions to wreck most or these transmittals. Yet this is not so at all. These ancient tales are constantly the inspiration of new explorations and scholarly investigations that keep bearing fruit. Even the tales of Eldorado has dug up a huge Indian civilization in the Amazon were our scholarship said such was impossible. My single regret is that we have inadvertently lost so much over the years that may have been instructive from this lode.
What I want to emphasize to my readers is that major climatic shifts all have reasonable apparent nonclimatic causation. In each case a significant shift of material took place. The Antarctic case sounds like a major ice sheet collapse that shifted the climatic circulation around. The second and third speak for themselves.
What is totally marvelous is that this has created a stunningly stable climatic system for the Northern Hemisphere which is not going to revisit the ice age for a likely million years or so. In fact, the only engine besides a super volcano that is capable of truly disturbing the climate is another ice sheet collapse and the evidence now suggests that could actually warm the climate rather than cool it. Both such events are ultimately temporary, but the victims will not be able to complain.
June 23, 2008
Ice Core Reveals How Quickly Climate Can Change
Weather patterns can permanently shift in as little as a year, according to the records preserved in an ice core from Greenland
By David Biello
Roughly 14,700 years ago the weather patterns that bring snow to Greenland shifted from one year to the next—a pattern of abrupt change that was repeated 12,900 years ago and 11,700 years ago when the earth’s climate became the one enjoyed today—according to records preserved in an ice core taken from the northern island. These speedy changes—transitions from warming to cooling and back again—in the absence of changes in greenhouse gas could presage abrupt, catastrophic climate change in our future.
"What made these abrupt climate changes were circulation changes, and these changes took place from one year to the next more or less," says glaciologist Sune Olander Rasmussen of the Centre for Ice and Climate at the University of Copenhagen, who was part of a team that analyzed annual data from ice tubes extracted from as deep as 10,000 feet (3,085 meters) beneath the ice sheet, which were collected by the North Greenland Ice Core Project, a drilling expedition.
The researchers looked at three variables in the core: the amount of dust, the kind of hydrogen and the kind of oxygen in the ice. The amount of dust from year to year reveals that less of the grit traveled all the way to Greenland from the deserts of Asia (where the dust that settles over Greenland originates) around the time these transitions began, the team reports in Science.
"If things are starting to change in the dust first then we are looking for a [climate change] trigger somewhere outside of Greenland," Rasmussen says. "That could be monsoon changes," since different rainfall patterns in Asia would affect dust levels in the atmosphere.
Roughly five years after this change in dust levels, the levels of heavy hydrogen ensconced in the ice indicate that weather patterns were shifting and driving precipitation over Greenland that had originated in evaporated water from a different area of the ocean than had previously been the source of the island’s rain. And this change happened in as little as a year. "During the glacial period, abrupt warmings show change of the atmospheric circulation from year to year," says glaciologist Dorthe Dahl-Jensen, also of the University of Copenhagen, who participated in the study as well.
Following this abrupt shift, as much as 20 degrees Fahrenheit (10 degrees Celsius) of warming occurred over the subsequent decades—a change that ultimately resulted in at least 33 feet (10 meters) of sea-level rise as the ice melted on Greenland.
Greenland can change quickly, even living up to its name, according to another paper in this week's Science. Sediment cores from the ocean show that forests of spruce and even fern grew on Greenland just 125,000 years ago. That means Greenland’s ice sheet—potentially responsible for as much as 75 feet (23 meters) of sea-level rise if it all melts—has grown and shrunk far more frequently than previously known.
"The question that arises from such findings is: How come the Greenland ice sheet at such a low latitude has remained so stable during the present interglacial [period] until now?" says study co-author and geochemist Claude Hillaire-Marcel of the University of Quebec in Montreal. "In view of the past instability—and sensitivity to temperature—of Greenland ice, serious concerns about its future under global warming stress do emerge."
Understanding that threat may require traveling even farther back in time via ice, to the transition to the last such warm period 130,000 years ago—the Eemian—when it was nine degrees F (five degrees C) warmer across Greenland. An ice core, known as NEEM (for North Greenland Eemian Ice Drilling), that could address that question is being extracted now as part of the ongoing International Polar Year. "The circulation changes in a few years. The temperature change is happening over decades," Rasmussen notes. "The more we force a system, the more likely it is that we will get some kind of response that is violent."
