Alister Doyle, PlanetArk 13 Nov 08;
OSLO - The planet could face a freeze worse than an Ice Age starting in as little as 10,000 years, giving future societies a headache the opposite of coping with global warming, scientists said on Wednesday.
The researchers, based in Britain and Canada, said that now-vilified greenhouse gases might help in future to avert a chill that could smother much of Canada and the United States, Europe and Russia in permanent ice.
They said the study, based on records of tiny marine fossils and the earth's shifting orbit, did not mean the world should stop fighting warming, stoked by human emissions of heat-trapping gases from burning fossil fuels.
"We're saying: 'don't push the panic button'," said Thomas Crowley, an American scientist at Edinburgh University who shared authorship of the study in the journal Nature with a colleague at Toronto University.
"There's no excuse for saying 'we've got to keep pumping carbon dioxide (CO2) into the atmosphere", he told Reuters by telephone, adding that the cooling was projected to start in 10,000 to 100,000 years.
"Geologically it's tomorrow," he said. "But we have a lot of time to argue about the appropriate level of greenhouse gases."
The projected build-up of vast ice sheets across the Northern Hemisphere and over seas around Antarctica would also lower sea levels by perhaps 300 metres (980 ft) -- connecting Russia to Alaska by land.
FALLING, RISING
In the last Ice Age, sea levels fell about 130 metres and much of Russia escaped a big ice sheet. Scientists can build sea level records from fossils because ocean chemistry varies; salt, for instance, is more concentrated when there is less sea water.
"Presumably, future society could prevent this transition indefinitely with very modest adjustments to the atmospheric CO2 level," they wrote. Greenhouse gases are widely blamed as the main cause of current warming that may bring more heatwaves, droughts, food shortages and rising seas.
A shift to a bigger blanket of ice would mark the end of a period of warming that began 50 million years ago, when even Antarctica was almost ice-free.
The scientists said the recent swings between Ice Ages and warmer periods such as the present, over the past 900,000 years, were getting sharper. Models suggested that instability could herald a shift to a new, far colder and stable state.
A similar shift happened more than 34 million years ago when Antarctica was first covered by ice, the scientists said. A trigger could be a slight growth of polar ice sheets, with ice and snow reflecting more of the sun's heat back into space. That could accelerate a cooling.
"Historians of science hate to say 'this is a special time'," Crowley said.
"But when you go through the models, each step seems reasonable and you get to an astonishing conclusion that we are right at the end of a 50-million-year evolution".
Modern human societies might never have developed if such a freeze had happened slightly earlier. "Anatomically modern humans evolved only 150,000 years ago," he said.
Crowley said more tests of the projections were needed.
"It might not come for tens of thousands of years," he said. "I'm sure some headline writers will want to say 'CO2 good for the atmosphere', or 'CO2 is good for us'. That's not the case."
(Editing by Tim Pearce)
Earth would be heading to a freeze without CO2 emissions
Yahoo News 12 Nov 08;
PARIS (AFP) – Scheduled shifts in Earth's orbit should plunge the planet into an enduring Ice Age thousands of years from now but the event will probably be averted because of man-made greenhouse gases, scientists said Wednesday.
They cautioned, though, that this news is not an argument in favour of global warming, which is driving imminent and potentially far-reaching damage to the climate system.
Earth has experienced long periods of extreme cold over the billions of years of its history.
The big freezes are interspersed with "interglacial" periods of relative warmth, of the kind we have experienced since the end of the last Ice Age, around 11,000 years ago.
These climate swings have natural causes, believed to be rooted particularly in changes in Earth's orbit and axis that, while minute, have a powerful effect on how much solar heat falls on the planet.
Two researchers built a high-powered computer model to take a closer look at these intriguing phases of cooling and warmth.
In addition to the planetary shifts, they also factored in levels of carbon dioxide (CO2), found in tiny bubbles in ice cores, that provide an indicator of temperature spanning hundreds of thousands of years.
They found dramatic swings in climate, including changes when Earth flipped from one state to the other in a relatively short time, said one of the authors, geoscientist Thomas Crowley of the University of Edinburgh, Scotland.
These shifts, called "bifurcations," appear to happen in abrupt series, which is counter-intuitive to the idea that the planet cools or warms gradually.
"You had a big change about a million years ago, then a second change around 650,000 years ago, when you had bigger glaciations, then 450,000 years ago, when you started to get more repeated glaciations," Thomas told AFP.
"What's also interesting is that the inter-glaciations also became warmer."
According to the model, published in the British journal Nature by Crowley and physicist William Hyde of Toronto University, Canada, the next "bifurcation" would normally be due between 10,000 and 100,000 years from now.
The chill would induce a long, stable period of glaciation in the mid-latitudes, smothering Europe, Asia and North America to about 45-50 degrees latitude with a thick sheet of ice.
However, there is now so much CO2 in the air, as a result of fossil-fuel burning and deforestation, that this adds a heat-trapping greenhouse effect that will offset the cooling impacts of orbital shift, said Crowley.
"Even the level that we have there now is more than sufficient to reach that critical state seen in the model," he said. "If we cut back [on CO2] some, that would probably still be enough."
In September, a scientific research consortium called the Global Carbon Project (GCP) said that atmospheric concentrations of CO2 reached 383 parts per million (ppm) in 2007, or 37 percent above pre-industrial levels.
Present concentrations are "the highest during the last 650,000 years and probably during the last 20 million years," the report said.
Crowley cautioned those who would seize on the new study to say "'carbon dioxide is now good, it prevents us from walking the plank into this deep glaciation'."
"We don't want to give people that impression," he said. "(...) You can't use this argument to justify [man-made] global warming."
Last year, the UN's Nobel-winning Intergovernmental Panel on Climate Change (IPCC) said that greenhouse-gas emissions were already inflicting visible changes to the climate system, especially on ice and snow.
Left unchecked, climate change could inflict widespread drought and flooding by the end of the century, translating into hunger, homelessness and other stresses for millions of people.
New Ice Age Predicted -- But Averted by Global Warming?
Mason Inman, National Geographic News 12 Nov 08;
Deep ice sheets would cover much of the Northern Hemisphere thousands of years from now—if it weren't for us pesky humans, a new study says.
Emissions of greenhouse gases—such as the carbon dioxide, or CO2, that comes from power plants and cars—are heating the atmosphere to such an extent that the next ice age, predicted to be the deepest in millions of years, may be postponed indefinitely.
"Climate skeptics could look at this and say, CO2 is good for us," said study leader Thomas Crowley of the University of Edinburgh in Scotland.
But the idea that global warming may be staving off an ice age is "not cause for relaxing, because we're actually moving into a highly unusual climate state," Crowley added.
In about 10,000 to 100,000 years, the study suggests, Antarctic-like "permanent" ice sheets would shroud much of Canada, Europe, and Asia.
"I think the present [carbon dioxide] levels are probably sufficient to prevent that from ever happening," said Crowley, whose study will appear tomorrow in the journal Nature.
Permanent Ice Sheets?
For the past three million years, Earth's climate has wobbled through dozens of ice ages, with thick ice sheets growing from the poles and then shrinking back again.
These ice ages used to last roughly 41,000 years. But in the past half a million years, these big freezes each stretched to about a hundred thousand years long.
Meanwhile, the temperature swings during and between these ice ages became more extreme, soaring to new highs and lows.
These extreme climate swings don't appear to be easing anytime soon, according to evidence recorded in Earth's rocks, Crowley said. "The latest two glaciations were two of the biggest we've seen."
The increasing variability is a sign that Earth's climate will soon move into a new state, according to a computer model used by Crowley and a colleague, William Hyde of the University of Toronto in Canada. They had previously used the model to simulate past ice ages.
The researchers found that between 10,000 and 100,000 years from now, Earth would enter into a period of permanent ice sheets—more severe than any seen in millions of years.
In some ways the ice age would be like those in the past few hundred thousand years, with a thick ice sheet covering North America, the study predicted.
But in the model, Europe and Asia also succumbed to ice sheets up to 2 miles (3.5 kilometers) thick, stretching from England to Siberia—something never before seen in models of past ice ages.
"We were surprised," Crowley said. "There's no evidence for this in Asia" during ice ages in the past few million years.
Hard to Know
Though this extreme ice age would be unusual, so is the climate that people are creating by emitting huge amounts of greenhouse gases, Crowley said (global warming fast facts).
"It's hard to say what's going to happen," Crowley said. "The very fact that you have this nonglacial [warming] atmosphere with polar ice caps [still present], presents a bizarre scenario.
"I don't know that we have a comparable analogy for it in the geologic record."
Prehistoric-climate expert Lorraine Lisiecki said, "This is the only study of which I am aware that suggests the next ice age could be much more extreme than those of the previous one million years."
Many more tests are needed to see if the study's prediction seems correct, said Lisiecki, of the University of California, Santa Barbara.
But she agreed that we might never find out what would have happened naturally, due to human-caused global warming.
"Current greenhouse gas concentrations are probably similar to those that occurred three million years ago and are high enough to prevent an ice age for hundreds of thousands of years," she said.
