9 June 2004Julianna Kettlewell
Analysis of the ice proves our planet has had eight ice ages during that period, punctuated by rather brief warm spells - one of which we enjoy today. If past patterns are followed in the future, we can expect our "mild snap" to last another 15,000 years. The data may also help predict how greenhouse gases will affect climate. |  Tiny bubbles of ancient air are locked in the ice |
Nobody quite knows how this will alter our climate, but researchers hope a detailed picture of past fluctuations will give them a better idea.
Distant worlds
A large team of scientists, from 10 different countries, has spent most of the last decade extracting the mammoth column of ice from a location called Dome C, on east Antarctica's plateau.
The European Project for Ice Coring in Antarctica (Epica) aims to unlock the climatic secrets of our past - and in doing so gain a better understanding of what we can expect in the future.
 The Antarctic camp was home to over 50 scientists |
Dome C contains 800,000 years worth of snowfall, allowing Epica to obtain a climate record two times longer than its nearest ice core rival.
"We think this project will really change the way we look at climate," said co-author Eric W. Wolff, of the British Antarctic Survey, Cambridge, UK.
Each slice of the ice core tells tales about the distant world it came from.
For instance, scientists can work out climate by looking at the ratio of different types, or isotopes, of hydrogen atoms.
Different colds
Deuterium is a heavy isotope of hydrogen. If a sample of ice has a lot of it, that means the temperature was warmer - and vice versa.
"At very cold temperatures a great deal of the heavy isotopes have rained out," explained Jerry F. McManus, of Woods Hole Oceanographic Institution, US. "So all that is left is what we would call isotopically depleted or lighter. That is how we know how cold it was."
He added: "You might say Antarctica is always cold - and you'd be right. But there is great variation in the degree of cold."
Another important thing that scientists can 'read' in the ice is the relative concentration of atmospheric gases.
That is because minute bubbles pock mark the core, within which tiny pockets of preserved air lie.
"That is the wonderful thing about ice cores," said Professor McManus. "There is air from three-quarters of a million years ago and it is still locked in these bubbles - it's incredible."
Turning which way?
Epica is still busy analysing the ice core's atmospheric gases, but preliminary results suggest that present CO2 levels are remarkably high.
"We have never seen greenhouse gases anything like what we have seen today," said Dr Wolff.
Over the last 800,000 years the Earth has, on the whole, been a pretty chilly place. Interglacials - or warm spells - have come every 100,000 years and have generally been short-lived.
Over the last 400,000 years, interglacials have lasted about 10,000 years, with climates similar to this one. Before that they were less warm, but lasted slightly longer.
We have already been in an interglacial for about 10,000 years, so we should - according to the pattern - be heading for an ice age. But we are not.
Predicting the future
The Epica team has noticed the interglacial period of 400,000 years ago closely matches our own - because the shape of the Earth's orbit was the same then as it is now.
That warm spell lasted a whopping 28,000 years - so ours probably will, too.
"The next ice age is not imminent," said Dr Wolff, "and greenhouse warming makes it even less likely - despite what The Day After Tomorrow says."
 Every chunk of ice-core tells tales about the distant world it came from |
"We will double the timescale over which we can study greenhouse gases," said co-author Thomas F Stocker, of the University of Bern, Switzerland. "We will be able to show what the natural variability is in relation to gases like CO2."
By understanding what greenhouse gases did to global temperature in the past, scientists might be able to predict the effect of humankind's enthusiastic CO2 belching.
"There is great controversy as to whether human beings have changed the climate," said Professor McManus. "But there is no doubt about the fact that human beings have changed the Earth's atmosphere. The increased levels of greenhouse gases are geologically incredible."
He added: "It is something of grave concern to someone like me, who sees the strong connection between greenhouse gases and climate in the past."
