The rapid rise in greenhouse gases over the past century is unprecedented in at least 800,000 years, according to a study of the oldest Antarctic ice core which highlights the reality of climate change.
Air bubbles trapped in ice for hundreds of thousands of years have revealed that humans are changing the composition of the atmosphere in a manner that has no known natural parallel.
Scientists at the British Antarctic Survey (BAS) in Cambridge have found there have been eight cycles of atmospheric change in the past 800,000 years when carbon dioxide and methane have risen to peak levels.
Each time, the world also experienced the relatively high temperatures associated with warm, inter-glacial periods, which were almost certainly linked with levels of carbon dioxide and possibly methane in the atmosphere.
However, existing levels of carbon dioxide and methane are far higher than anything seen during these earlier warm periods, said Eric Wolff of the BAS.
"Ice cores reveal the Earth's natural climate rhythm over the last 800,000 years. When carbon dioxide changed there was always an accompanying climate change," Dr Wolff said. "Over the past 200 years, human activity has increased carbon dioxide to well outside the natural range and we have no analogue for what will happen next.
"We have a no-analogue situation. We don't have anything in the past that we can measure directly," he added.
The ice core was drilled from a thick area of ice on Antarctica known as Dome C. The core is nearly 3.2km long and reaches to a depth where air bubbles became trapped in ice that formed 800,000 years ago.
"It's from those air bubbles that we know for sure that carbon dioxide has increased by about 35 per cent in the past 200 years. Before that 200 years, which is when man's been influencing the atmosphere, it was pretty steady to within 5 per cent," Dr Wolff said.
The core shows that carbon dioxide was always between 180 parts per million (ppm) and 300 ppm during the 800,000 years. However, now it is 380 ppm. Methane was never higher than 750 parts per billion (ppb) in this timescale, but now it stands at 1,780 ppb.
But the rate of change is even more dramatic, with increases in carbon dioxide never exceeding 30 ppm in 1,000 years -- and yet now carbon dioxide has risen by 30 ppm in the last 17 years.
"The rate of change is probably the most scary thing because it means that the Earth systems can't cope with it," Dr Wolff told the British Association meeting at the University of East Anglia in Norwich.
"On such a crowded planet, we have little capacity to adapt to changes that are much faster than anything in human experience."Reuse content