Azara Blog: Analysis of a previous period of global warming

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Date published: 2006/02/18

The BBC says:

Greenhouse gases are being released 30 times faster than the rate of emissions that triggered a period of extreme global warming in the Earth's past.

That is the conclusion of scientists who presented results at a conference in St Louis, in the US.

Emissions that caused a global warming episode 55 million years ago were released over 10,000 years.

Burning fossil fuels is likely to release the same amount over the next three centuries, the scientists claim.

Professor James Zachos of the University of California at Santa Cruz studied the period of global warming known as the Palaeocene-Eocene Thermal Maximum (PETM).

Temperatures shot up by 5C (9F) during this episode, driven by a massive release of carbon dioxide and methane into the atmosphere.

By probing sediments on the ocean floor, Professor Zachos was able to determine that about 4.5 trillion tonnes of carbon entered the atmosphere over a period of 10,000 years.

If present trends continue, this is the same amount that will be emitted by burning fossil fuels during the next 300 years, according to the UC Santa Cruz geologist.

The fear for climate scientists is that higher temperatures could slow down ocean mixing, reducing the ocean's capacity to absorb CO2. This could cause "positive feedback", with reduced absorption leaving more CO2 in the air, causing more warming.

"Records of past climate change show that change starts slowly and then accelerates," he said.

"The system crosses some sort of threshold."

This is a slightly apples and oranges comparison since the atmosphere is not the same now as then. And of course that assumption about how much carbon will be released into the atmosphere over the next 300 years is just that, an assumption (you can just about believe analyses about the next 20 or maybe even 50 years, but not 300). But it does show, as everybody already knew, that we are pumping an awful lot of carbon into the atmosphere here and now.

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