How do we know climate change is coming? Testing of ancient ice provides some clues, writes Dick Ahlstrom
If you want to understand our evolving climate, look no further than your nearest icicle. It can tell you a great deal about past climate - provided you can find one that hasn't melted.
Ancient ice has provided us with an unbroken string of climate data going back 800,000 years, states Dr Eric Wolff, a senior scientist with the British Antarctic Survey.
While an icicle might take you back a century or two, Dr Wolff relies on ice of a different kind, drilled out of the great ice sheets that cover Antarctica and Greenland.
He chairs the scientific group in the European Project for Ice Coring in Antarctica, and is one of the survey's experts in the use of ice cores to understand past climate.
He visited Dublin this week to deliver one of a continuing series of lectures on climate change organised by the Environmental Protection Agency.
"We need to understand the past if we want to understand the future," Dr Wolff said of the Earth's climate earlier this week. And there is no better place to look for this understanding than in the tiny bubbles trapped inside ancient ice.
"Polar snow falls and doesn't melt, so it builds up over time and gets squashed into ice. You can go through the ice layer by layer and in the Antarctic we have gone back 800,000 years, covering eight cycles of the Earth going through ice ages," Dr Wolff explains.
Expeditions have recovered cores reaching down 3,200m through the ice, laboriously brought up in sections of three to four metres each. These cores provide huge amounts of climatic information however, much of it recovered from the tiny air bubbles locked in the ice.
"The bubbles are probably the most interesting part of the ice core because they contain a detailed picture of the climate at the time they were formed, pockets containing air hundreds of thousands of years old," he says.
"You use a saw to cut a cube of ice, put it into a vacuum chamber to suck out the modern air and then you open the bubbles up with needles to release the old air."
This is drawn off and analysed, delivering a wealth of information. It gives ambient carbon dioxide levels and can tell you about volcanic activity based on sulphur dioxide content.
Temperature levels are also revealed by studying the melted ice. It provides estimates of temperature by measuring the ratio of different isotopes found in the water.
These estimates are accurate to about one degree either way, Dr Wolff adds.
The core findings so far are conclusive on how our atmosphere has changed over the centuries.
"Carbon dioxide has really gone up, 35 per cent from its natural level in just 200 years. It is much higher than it has ever been over the last 800,000 years," Dr Wolff says.
The latest figures indicate carbon dioxide levels have reached about 382 parts per million. Levels over the millenniums have typically ranged between 280 and 300 parts per million. And average Antarctic temperatures are now nine degrees higher than 20,000 years ago.
"The one thing we can't do is say we have a [ future] analysis based on information from the past. Carbon dioxide has never been as high," he adds. We are in completely new territory with these high levels and have nothing with which to compare.
This does not thwart attempts to make predictions about the future, however. Past data is used to test models and see if they can make good predictions about past events.
"It is a way to see if the model we want to use to read the future understands the past," Dr Wolff explains.
The models are still weak at predicting regional effects but better at the global climatic response and all predictions point to continued warming. "We are expecting warming over the next decade and this is expected to be stronger in the Arctic and Antarctic. The big implication is sea level."
WE COULD SEE a one metre rise in sea level over the next 100 years. "There is also the issue whether this would affect ocean currents. I think the jury is out on that," he adds.
"There is a lot to worry about in the predictions, but it may not be as bad as suggested. The problem is it doesn't matter how small the change or whether it is natural or man made because it is happening whatever the cause," he argues.
The warming is real, the ice is melting and we will have to deal with the changes that come.
See the Environmental Protection Agency's lecture series on its website www.epa.ie/news/events/