Ice cores give up 800,000 years of climate data

Scientists working on ice cores drilled in the Antarctic have obtained data on the climate and atmospheric greenhouse gas concentrations going back 800,000 years. Among other things, the cores reveal that the levels of greenhouse gases in the atmosphere today are higher than a...

Scientists working on ice cores drilled in the Antarctic have obtained data on the climate and atmospheric greenhouse gas concentrations going back 800,000 years. Among other things, the cores reveal that the levels of greenhouse gases in the atmosphere today are higher than at any point in the last 800,000 years.

The study also confirms the close link between greenhouse gas levels and climate change. 'The temperature curve over the past 800,000 years matches the CO2 curve beautifully - during glacial periods in which the climate is cold, there is less CO2 in the atmosphere,' explained Thomas Blunier of the University of Copenhagen, who was involved in the study. This new information on how greenhouse gases influence the temperature will be of help to scientists attempting to predict future climate changes.

The ice cores were obtained by the EU-funded EPICA (European Project for Ice Coring in Antarctica) Project. The 3,270 metre core covers eight long glacial periods and eight shorter, warmer interglacial periods and extends our knowledge of how the climate changed in the past by some 150,000 years. Earlier work by the EPICA team took our knowledge back to 650,000 years before the present.

The researchers determined the temperature in the past by studying the mix of water isotopes in the ice, while information on atmospheric greenhouse gas concentrations was gathered from tiny air bubbles enclosed in the ice. Their findings are published in two papers in the latest edition of the journal Nature.

The first paper investigates how carbon dioxide (CO2) levels have changed over the millennia. Currently, CO2 levels stand at just over 380 parts per million (ppm), which is 28% higher than during the pre-industrial era. The research revealed that during a glacial period that occurred between 650,000 and 750,000 years ago, the CO2 level was at its lowest level, falling below 180ppm.

The second paper looks at another important greenhouse gas: methane (CH4). The current concentration of methane in the atmosphere is around 1,800 parts per billion; which is 124% higher than in previous periods. The ice core revealed that the curve for methane closely matches the temperature curve.

Crucially, the EPICA research uncovered evidence of rapid climate changes in the past; around 770,000 years ago, levels of both CO2 and CH4 changed drastically within just a few decades. Similar changes also took place around 40,000 years ago during the last glacial period. These could have been caused by changes in ocean circulation patterns, the scientists speculate.

The next step for the ice core community is to obtain a core comprising a continuous climate record going back 1.5 million years. In the framework of the International Partners in Ice Core Sciences (IPICS), researchers are already hunting for a suitable site; the search is expected to take several years.