| The human fossil fuel emission is unprecedented on geological timescales. The best science can’t find any time in all of Earth’s geological history that produced a rate of atmospheric carbon accumulation equal to the one that’s happening now.|
A new study recently published in Nature sheds more light on this. Scientists had to look far back in time. All the way back when the last of the Dinosaurs were dying off about 55-66 million years ago. The most recent Hothouse Mass Extinction Event in the geological record is called the Paleocene-Eocene Thermal Maximum or PETM. It’s an extreme period of rapid warming that occurred at the boundary between these two periods of Earth's history about 55.8 million years ago.
|The PETM was bad. It set off a mass extinction in the oceans which wiped out half of all shellfish through the varied impacts of anoxia, acidification and coral bleaching. Its heat forcing was enough to reverse ocean circulation and set up a stratified ocean. |
Peatlands and forests went up in flames. Extreme surface temperatures forced a mass poleward migration. Scientists found that the large carbon emission occurred over the course of about 4,000 years. This spike in atmospheric carbon coincided with a 5 degree Celsius spike in global temperatures in a 4,000 to 12,000 year time period. This implies a rate of warming of at most around 0.12 degrees Celsius every 100 years.
|Expected human warming of between 1.5 and 5 degrees Celsius this century is therefore at least 15 to more than 200 times faster than during the PETM extinction event. On average, over the PETM extinction event, rates of atmospheric carbon accumulation were found to be in the range of about 1.1 billion tons per year. By comparison, human carbon emissions during 2014 were about ten times this level at around 10 billion tons.|
The rate of emission could jump to as high as 25 billion tons of carbon per year by 2050.