Volcanic eruptions 55 million years ago were responsible for the worst global warming the planet has known, but pale beside what mankind could do, a study shows. Eruptions along a 1,200-mile ridge pumped an estimated 4,000 to 5,000 gigatonnes of carbon into the atmosphere in about 10,000 years, warming the oceans by about 5 to 6C (9 to 10.8F).

But with humans pumping out eight gigatonnes every year, a figure that is rising, it will take mankind only 600 years to match the quantity emitted by the volcanoes that tore apart the European and North American continents.

The eruptions took place along the eastern side of what is now Greenland, and the volcanic activity split the two continents and pushed them apart, creating the North Atlantic Ocean. So much greenhouse gas, mainly carbon dioxide and methane, was emitted that it created what scientists call “a planetary emergency”.

The sudden surge in carbon emissions was, the study suggests, caused when magma from the increased volcanic activity forced its way into stockpiles of organic material collected over tens of thousands of years from dead animal and plant matter. As these “compost heaps” were cooked by the magma, they released trapped carbon.

Some of the organic material might have formed into oil and gas, and the huge quantities of carbon emitted turned the Arctic seas subtropical.

Michael Storey, a British scientist based at Roskilde University in Denmark, led the research, which established the link between the increase in volcanic activity 55 million years ago and the rise in temperatures. The period of global warming is called the Paleocene-Eocene thermal maximum (PETM) and the mechanisms which caused it have long puzzled scientists.

It is ideal to study for climate change science, said researchers, because it offers evidence of how carbon emissions occur, how they cause temperatures to rise and how long it takes – 100,000 years in the case of the PETM – to recover. The study, published in the journal Science, suggests that volcanic activity destroying sedimentary stocks of organic material was the main driver.

“Imagine how much carbon would be released if lava found its way into an oil field,” said Dr Storey. “That’s the sort of scenario on a vast scale that we’re talking about.”

The finding that organic stocks were the key reservoir for carbon emissions offers some optimism for the future. One fear is that, as the oceans warm, they will release greater quantities of methane hydrates, one of the most damaging contributors to global warming.

By finding that the PETM was likely to have been caused by volcanic magma cooking organic materials, the study suggests that warming of the oceans is less dangerous today than feared. PETM carbon levels rose dramatically, and led to 30-50 per cent of deep sea creatures becoming extinct, but nowhere near as quickly as is happening today.

Dr Storey said: “PETM is a remarkable geological event in which a large amount of greenhouse gases were released. In geological terms it happened in the blink of an eye. We are set to achieve in a few hundred years what took nature 10,000 years.”

Peter Cox, of Exeter University, said the PETM was important because of its dramatic increase in carbon emissions. “It’s the only one that’s even close to the rate that we are likely to impose, though it’s really rather slow compared to what we are doing at the moment.”

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