Study reduces lag between CO2 release and warming

Thursday 30th Aug 2012 by theWeather Club

Scientists have shed new light on one of the most important questions in climate science: the time lag between changes in temperature and changes in atmospheric carbon dioxide levels in the past. Their findings suggest that feedbacks in the climate system – in which warming is linked to natural carbon dioxide increase, driving further warming – may operate faster than previously thought.

In a paper published in Climate of the Past, the researchers use Antarctic and Greenland ice cores to examine temperature and carbon dioxide changes during the largest natural climate change in Earth's recent climate history: the warming out of the last ice age. As past Antarctic temperatures increased, ocean circulation was altered and carbon dioxide - most likely from the deep Southern Ocean - escaped into the atmosphere. Previous studies had suggested that it took up to 1000 years for this to happen. But the new study, drawing on data from five separate ice cores that figure.

"The ice cores reveal a near-synchronous temperature and carbon dioxide increase. If there was a lag at all then it was likely no more than 400 years," says Dr Joel Pedro from the Antarctic Climate and Ecosystems CRC, in Hobart, who led the study.

One of the burning issues that study raises is whether current anthropogenic warming may drive additional natural carbon dioxide increases sooner than we thought, compounding the climate change problem. Dr Pedro acknowledges that the research raises this possibility, but cautions that a firm answer on whether we need to revise thinking on the timescales of carbon cycle response to anthropogenic warming requires further research.

Dr Pedro says that there are similarities but also important differences between current climate change and the natural processes described in their research.

"The coupled rise in temperature and natural increase in carbon dioxide that helped end the ice age took place gradually, over about 8000 years. What we have seen since the start of the industrial revolution is a similar carbon dioxide increase occurring over only a few hundred years. This is way faster than anything in the ice core record and it's clearly human-caused. Just as the steady increase in carbon dioxide helped to melt the ice caps and warm the Earth out of the ice age, the rapid increase now in carbon dioxide is also driving up temperatures, only at a much faster rate," he said.