About 55 million years ago, massive amounts of greenhouse gases flooded the earth’s atmosphere causing rapid global warming. The time was transitional between the Paleocene Epoch and the Eocene Epoch, giving rise to the name: Paleocene-Eocene Thermal Maximum, or PETM.
Average global temperatures reached as high as 27 degrees Celsius, or 13 degrees higher than the average global temperature today. The rate of global temperature rise leading to the PETM was extremely high from a geological perspective, but still about 25 times less than the rate of Anthropogenic temperature rise we see today. The PETM temperature spike saw the planet warm by 5 degrees Celsius (9 degrees Fahrenheit) over about 20,000 years. Sea level was 300 feet higher than today because of melting ice and thermal expansion of the seawater.
The geological data are clear that atmospheric carbon dioxide (CO2) increased dramatically during the PETM, and also, the earth’s oceans experienced rapid acidification. In total, an estimated 10 trillion tons of carbon entered into the atmosphere to create the PETM. However, the causes of atmospheric carbon increase are speculative. I discussed one plausible theory regarding massive releases of methane from ocean bottom clathrates in my article “An ancient analog to global warming.”
North Atlantic volcanism
Recent work (Jones et al., 2019) supports an alternative theory that the carbon source, which initiated the PETM, was related to large scale volcanism as opposed to ocean bottom methane clathrates. Accordingly, this work notes the proximity in time between the formation and early history of the Icelandic Plume and the PETM.
The mantle plume responsible for the Iceland Hotspot formed about 60 million years ago as part of the opening of the North Atlantic, when North America and Europe parted ways. About four million years later (immediately before the PETM) a massive pulse of molten mantle rock rose through the Plume and towards the surface. This magma pulse then uplifted the earth’s surface, creating a land bridge between Greenland and Scotland.
However, this pulse of magma didn’t all make it to the earth’s surface. Instead, massive amounts of magma were injected into the thick marine sediments of the North Atlantic sedimentary basin. Geologists refer to layers of magma injected into cooler rocks as “sills”. So, the marine sediments were laden with organic matter, and heat from the magma cooked that organic material, generating thermogenic methane.
Researchers looking at seismic data detect signs that the gases generated from this process vented to the surface where they passed into the atmosphere. The amount of gas generated by any single sill is small, but the research estimates up to 18,000 sills in the North Atlantic Igneous Province.
What does this mean for the Anthropocene
The researchers used standard oil field kinetics for modeling the transformation of organic material into methane. These kinetics were then integrated with the sill data to run stochastic models for predicting total methane output from the magmatic pulse in the late Paleocene to early Eocene. The results of this modeling support the theory that near-surface volcanic activity could have generated enough methane to account for the PETM temperature spike.
The PETM serves as a reminder that rapid global warming is possible under natural conditions. This observation applies regardless of whether the source of the carbon was volcanic derived methane or methane from sea bottom clathrates. This recent research into a volcanic origin for the PETM carbon indicated that up to a gigaton of carbon was released into the atmosphere each year for 10 to 20 thousand years. Remember that global fossil fuel emissions in 2018 were approximately 37 gigatons.
This magnitude of difference in greenhouse gas emissions between the PETM and now is in line with the observation that the rate of global yearly temperature increase today is about 25 times greater than temperature rises during the PETM. This connection between past and present certainly provides food for thought.
An ancient analog to global warming (Source: ArcheanWeb) – https://archeanweb.com/2019/12/17/an-ancient-climate-tipping-point-analog-to-global-warming/ Also:
The Icelandic Plume (Source: ArcheanWeb) – https://archeanweb.com/2020/03/25/the-icelandic-plume/ Also:
An Ancient Magma Flood Offers Clues About Global Warming (By Howard Lee; Wired) – https://www.wired.com/story/an-ancient-magma-flood-offers-clues-about-global-warming/ Also:
Large Igneous Province thermogenic greenhouse gas flux could have initiated Paleocene-Eocene Thermal Maximum climate change (By Stephen M. Jones, Murray Hoggett, Sarah E. Greene & Tom Dunkley Jones; 2019; Nature Communications) – https://www.nature.com/articles/s41467-019-12957-1 Also:
Feature Image: Nyiragongo lava lake (By Radio Okapi) (Modified) – https://commons.wikimedia.org/wiki/File:Nyiragongo_lava_lake.jpg – This file is licensed under the Creative Commons Attribution 2.0 Generic license. – https://creativecommons.org/licenses/by/2.0/deed.en