Once again: It's warming that triggered a CO2 rise -- not vice versa

Changes in the Earth’s orbit 55million years ago caused the planet to warm up by 5C, according to new research. A study by climate scientist Rob DeConto of the University of Massachusetts Amherst and colleagues at the University of Sheffield found that orbital changes triggered the melting of vast areas of permafrost at the poles, which released greenhouse gas carbon dioxide into the atmosphere.

The extreme warming events were called the Paleocene-Eocene Thermal Maximum (PETM) and took place over thousands of years.

Previously it was thought that the oceans were the source of the carbon. ‘The standard hypothesis has been that the source of carbon was in the ocean, in the form of frozen methane gas in ocean-floor sediments,’ DeConto said.

‘We are instead ascribing the carbon source to the continents, in polar latitudes where permafrost can store massive amounts of carbon that can be released as carbon dioxide when the permafrost thaws.’

DeConto's team used a new, high-precision geologic record from rocks in central Italy to show that the PETM occurred during periods when Earth's orbit around the sun was both highly eccentric - non-circular - and oblique, or tilted.

Orbit affects the amount, location and seasonality of solar radiation received on Earth, which in turn affects the seasons, particularly in polar latitudes, where permafrost and stored carbon can accumulate.

They then simulated climate-ecosystem-soil interactions, accounting for gradually rising greenhouse gases and polar temperatures plus the combined effects of changes in Earth orbit.

Their results show that the magnitude and timing of the PETM can be explained by the orbitally triggered decomposition of soil organic carbon in the circum-Arctic and Antarctica.

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