Around 56 million years ago, there was a sudden massive release of carbon into the atmosphere, which caused the planet’s temperature to spike – an event that has come to be known as the Paleocene-Eocene Thermal Maximum (PETM). Researchers have used this as something of an analogue to help understand how the current increase in atmospheric CO2 might impact our climate. But now it seems that the PETM was just a blip compared to the rate at which we’re currently emitting carbon.
By analyzing the sediment laid down at the bottom of oceans when the PETM kicked off, researchers have been able to work out just how much carbon was released during the event, and how quickly. They found that it took around 4,000 years with around 0.6 to 1.1 billion tonnes (0.7 to 1.2 bllion tons) of carbon being released per year for the PETM to reach its maximum. At this point, global atmospheric carbon settled at around 1,000 parts per million, causing global temperatures to increase by 5°C (8°F).
In contrast, humans are currently emitting close to 40 billion tonnes (44 billion tons) of CO2 per year, with the amount of carbon in the atmosphere already tipping 400 parts per million. Published in Nature Geoscience, the research shows that the release of carbon during the PETM was vastly smaller than what we are currently emitting, meaning that any conclusions drawn from it will have limited applications to today’s situation.
Info on PETM here. How deadly was it?
The sediment sample. The red band marks the PETM at around 56 million years ago. James Zachos
“As far as we know, the PETM has the largest carbon release during the past 66 million years,” explains Richard Zeebe, who co-authored the paper, in a statement. Yet even a natural event of this scale might not be able to tell us very much. “Because our carbon release rate is unprecedented over such a long time period in Earth's history, it also means that we have effectively entered a 'no-analogue' state. This represents a big challenge for projecting future climate changes because we have no good comparison from the past.”
What exactly caused the PETM is still up for debate, from meteors to massive methane leaks to a mix of these things. This study doesn’t attempt to answer this, but simply looks at the result of it. During the period after the event, there were massive changes in the animals surviving and evolving across all ecosystems. But it now seems that they also had a much longer period of time over which to adapt – thousands of years – compared to the current event we’re going through, which is happening in just a hundred.