The Earth has suffered a planetary fever before. Around 56 million years ago, temperatures rose between nine and 15° Fahrenheit (5-8°C), during the transition between the Paleocene and the Eocene, known to scientists as the Paleocene-Eocene Thermal Maximum (PETM). It lasted over 200,000 years, until carbon levels were rebalanced.
The result of a carbon spike, it has been the subject of numerous scholarly papers, and debates over the roots of the carbon injected into the Earth’s atmosphere continue through today. Yet the question that continues to plague researchers is, “Where did all the carbon come from?” We know the current source of the excess carbon pouring into the atmosphere: Us. But humans weren’t around 56 million years ago (our ancestors were still primates).
Theories have ranged from volcanic releases of oceanic methane, to an influx of carbon from a comet impact. New research published in the journal Nature Geoscience indicates that this severe global warming spike was caused by not one but actually two injections of carbon and other greenhouse gases into the atmosphere. This is a significant observation because it allows researchers to assess exactly what triggered the carbon spike of the PETM.
Scientists believe that this evidence can be used to estimate the impacts of global warming now. Not all researchers have been convinced on this juxtaposition, seeing it as a false scientific cognate of paleohistory to the contemporary era. Some studies have suggested that atmospheric carbon built up over 20,000 years, making its impact too slow to compare to the present day. Other studies have suggested that the soaring carbon could have occurred over just a few years—in other words, that it happened too fast to compare to modern times.
But the researchers of the Nature Geoscience study argue that the evidence of a two-time burst of carbon instead suggests that the rate of change was probably “just right” for making modern comparisons.
The results of the research indicate that carbon was pumped into the atmosphere over a period of a few thousand years. Just how much carbon was injected into the atmosphere during the PETM is uncertain, but it is estimated to be roughly the amount that would be injected today if all carbon fuels on Earth were burned through.
Scientists also found that at least 992 million tons of carbon entered the atmosphere per year. That is within an order of magnitude of today’s annual rate of 10.5 billion tons.
The majority of modern greenhouse gas emissions has occurred within the last two centuries, not dramatically over a few thousand years. Furthermore, it seems to be a logical leap to say that roughly 1 billion tons of carbon is somehow the same as 10 billion tons. The amount of carbon emissions today still exceeds that seen 56 million years ago by a long shot, owing to factors of both time span and sheer volume. Even if this evidence suggests it is closer to our current climate warming crisis than previously thought, it is still isn’t really in the ballpark.
Keeping global warming below the 2°C threshold is a critical to maintaining global stability. The PETM saw 5-8° C increase, and although the planet did not immediately erupt into flames, an unknown and perhaps innumerable number of species perished or mass migrated. Furthermore, this was still over a period of several thousand years, rather than the current outlook of a generation or two that will face devastatingly high sea levels.
The PETM brought on a number of extreme weather conditions including drought and floods, insect plagues, and at least a handful of extinctions. However, life did indeed prosper throughout the PETM—the evolutionary consequences surround us, and in fact include us. But it is difficult to tell what damage was done in the process.
And we may not come out on the other side of another 200,000 year stretch.