For instant climate change, just add one large comet

New Scientist

Image: Space Art

A comet may have sent temperatures soaring 55 million years ago.

Two geologists claim they have evidence that carbon dioxide levels in Earth’s atmosphere more than doubled in a single year at the end of the Palaeocene. The increase helped trigger the most extreme change in surface temperatures since dinosaurs ruled the land. The speed of the change makes an extraterrestrial impact the likely cause, they say.

Global temperatures rose by about 5 °C at the end of the Palaeocene – an event known as the Palaeocene-Eocene Thermal Maximum (PETM). Because more CO₂ in the atmosphere makes the oceans more acidic, the event can be tracked by looking at the amount of calcium carbonate deposited on the ocean floor by marine organisms. In more acidic waters, less is deposited. Sediment analysis has suggested the increase in CO₂ that caused the PETM took between 750 and 30,000 years.

But James Wright and Morgan Schaller at Rutgers University in Piscataway, New Jersey, think it happened much more rapidly. They analysed sediments from a shallow Atlantic Ocean shelf where sediment accumulates faster than it does in the deep sea, making it easier to see seasonal fluctuations in the amount deposited. The pair say that within just one annual cycle about 55 million years ago, the amount of calcium carbonate laid down dropped by 5 per cent. This suggests a very sudden addition – within a year – of atmospheric CO₂ (PNAS, doi.org/n8t). Read more on newscientist.com…