The Courier-Mail
Global warming has increased at unprecedented rates since the 1950s, new research of ice cores from the past 200,000 years shows.
"The past few decades have been unique in the past 200,000 years in terms of the changes we see in the biology and chemistry recorded in the cores,'' University of Colorado glaciologist Yarrow Axford said, announcing the study by Canadian and US researchers published in Proceedings of the National Academy of Sciences.
"We see clear evidence for warming in one of the most remote places on Earth at a time when the Arctic should be cooling because of natural processes.''
For thousands of years, environmental changes in a remote lake on Canada's Baffin Island matched natural, cyclical climate changes such as those caused by the Earth's periodic wobble as it swung around the sun, the researchers said.
But lake sediment cores dating from 1950 showed expected climate cooling was overridden by human activity like greenhouse gas emissions.
Researchers reconstructed the local climate over the past 200,000 years by analysing algae, insect fossils and geochemical traces in sediment cores extracted from the 40ha lake.
The cores stretch back 80,000 years further than existing Greenland ice cores, revealing environmental conditions during two earlier ice ages and three interglacial periods.
Researchers found several types of mosquito-like midges, that for many thousands of years thrived in cold climate surrounding the lake, suddenly began declining about 1950 and two midge species adapted to the coldest weather disappeared.
"Our results show that the human footprint is overpowering long-standing natural processes even in remote Arctic regions,'' said study co-author John Smol, of Canada's Queen's University in Kingston, Ontario.
Another study published in September in Science magazine that reconstructed 2000 years of Arctic temperatures from ice and lake sediment cores and tree rings, found the recent global warming trend was overriding a natural cooling caused by Earth's periodic wobble.
The Earth was now about 960,000km further from the sun during the Northern Hemisphere summer solstice than it was 2000 years ago, causing an overall cooling of the Arctic until recently, said the researchers.