DNA hints warm era didn't melt entire cap.
An international team of scientists, drilling deep into the ice layers of Greenland, has found DNA from ancient spiders and trees, evidence that suggests the frozen shield covering the immense island survived the earth's last period of global warming.
The findings, published today in the journal Science, indicate Greenland's ice may be less susceptible to the massive meltdown predicted by computer models of climate change, the article's main author said in an interview.
"If our data is correct, and I believe it is, then this means the southern Greenland ice cap is more stable than previously thought," said Eske Willerslev, research leader and professor of evolutionary biology at the University of Copenhagen. "This may have implications for how the ice sheets respond to global warming. They may withstand rising temperatures."
Scientists not involved in the study cautioned, however, that current climate change is so driven by pollution from power plants, industry, and other human activity that it is nearly impossible to draw a meaningful conclusion about the durability of Greenland's ice.
"Whatever occurred in the past almost surely occurred much more slowly," said Raymond S. Bradley, director of the Climate System Research Center at the University of Massachusetts at Amherst. "Human activity is pushing warming at a much faster rate than in the past. Change is occurring in decades or centuries, not over millennia."
A painstaking analysis of surviving genetic fragments locked in the ice of southern Greenland shows that somewhere between 450,000 and 800,000 years ago, the world's largest island had a climate much like that of Northern New England, the researchers said. Butterflies fluttered over lush meadows interspersed with stands of pine, spruce, and alder.
Greenland really was green, before Ice Age glaciers enshrouded vast swaths of the Northern Hemisphere.
More controversially — and as an example of how research in one realm of science can unexpectedly affect assumptions in another — the discovery of microscopic bits of organic matter retrieved from ice 1.2 miles beneath the surface indicates that the ice fields of southern Greenland may be more resilient to rising global temperatures than has been forecast. The DNA could have been preserved only if the ice layers remained largely intact.
A scenario often raised by global warming specialists is that Greenland's ice trove will turn liquid in the rising temperatures of coming decades, with hundreds of trillions of gallons of water spilling into the Atlantic. This could cause ocean levels worldwide to rise anywhere from 3 to 20 feet, according to computer projections — bad news for seaport cities like Boston.
But the discovery of organic matter in ice dating from half-a-million years ago offers evidence that the Greenland ice shield remained frozen even during the earth's last "interglacial period" — some 120,000 years ago — when average temperatures were 9 degrees Fahrenheit warmer than they are now. That's slightly higher than the average temperatures foreseen by most scientists for the end of this century, although some environmentalists warn it might get even hotter.
Researchers from the Danish-led team said the unanticipated findings appear to fly in the face of prevailing scientific views about the likely fate of Greenland's thickly-layered ice, although Willerslev stressed that the findings do not contradict the basic premise that the earth's temperature is rising to worrisome levels, with gases emitted by industry, cars, and other human activity playing a big role.
"But it suggests a problem with the [computer] models" that predict melting ice from Greenland could drown cities and destroy civilizations, according to Willerslev.
"We should remain very worried about rising sea levels," he said. "We know that during the last interglacial, sea levels rose by 5 meters or more. But this must have come from sources additional to Greenland, such as Antarctic ice. It does not appear the whole [Greenland] sheet will melt."
Computer models suggest that Greenland and Antarctica will be the main contributors to rising sea levels as the climate warms. (The Arctic won't affect sea level, because its ice already floats in the ocean.)
Some scientists not involved in the study drew a conclusion very different from that of the Danish-led team .
"The raw results of this study are very impressive — southern Greenland was unglaciated sometime during the last million years or so," said Gavin Schmidt, a climatologist with National Aeronautics and Space Administration 's Goddard Institute for Space Studies. "I would argue that this implies a more unstable ice sheet, not the opposite."
Schmidt said that during the more recent warming period, most but not all of the ice might have disappeared from southern Greenland, leaving a thin layer that would have been sufficient to preserve the DNA.
The organic matter found in ice cores taken from a southern Greenland drilling site known as Dye 3 represent s the oldest-ever authenticated DNA found by scientists to date, with fragments of beetles, tree bark, prehistoric spiders, and other life verified independently in laboratories in Denmark, Canada, and Germany.
"The ice sheet served as a deep freezer, preserving organic materials for amazingly long periods," said Martin Sharp, a University of Alberta glaciologist who participated in the Greenland research.
Scientists were able to isolate only about 1.6 ounces of organic matter from the ice at the bottom of the core sample, according to Enrico Cappellini, a researcher specializing in ancient proteins at Britain's University of York.
But that was enough to extract genetic traces of long-vanished plants and insects, enabling scientists to envision in fine detail a prehistoric landscape.
"The genetic material presents a biological environment that is completely different from the Greenland we see today," said Willerslev. "We found grain, pine, yew, and alder. We found traces of spiders, beetles, ancient butterflies."
The identifications were made by comparisons with genetic material from existing species.
Analysis of the insect mitochondria, cellular components that contain genomes that can be used to date DNA, as well as amino acids, indicate d that the creatures were at least 450,000 years old. Uncertainties with dating, however, leave the possibility that the DNA dated only as far back as the last interglacial period.
The identification of such relatively well-preserved genetic material beneath ice sheets was exciting news for biologists. Ten percent of the earth's surface has been covered by deep ice for tens of thousands of years. "We could be opening up a frozen world of new discoveries," said Cappellini, the University of York researcher.
In terms of its name, Greenland was the original snow job.
Erik the Red — a famous Viking banished first from Norway and then Iceland for murdering his neighbors — sailed his longship to the uninhabited island in 982 AD. Showing an intuitive flair for PR, Erik sent back word of a bountiful "green land" as a way of enticing others to follow him to fjords at the southwestern tip of the island. In medieval times, the climate in the region was just warm enough to permit cultivation of some rugged crops and the raising of livestock.
The Nordic settlements — the first European presence in the New World — survived for nearly 500 years before mysteriously disappearing. Historians speculate that either the inhabitants starved as Greenland grew colder or they were killed by Inuit, who appeared on the scene around 1200 AD.
Colin Nickerson can be reached at firstname.lastname@example.org.