Can volcanoes overheat the Earth?

A geyser in Iceland is part of the Central Atlantic rift system where volcanic activity may have caused an extreme global warmup about 56 million years ago. @bberwyn photo.

Study says ancient extreme global warming event was caused by C02 buildup from massive eruptions

Staff Report

The role of volcanoes on Earth’s climate is complex. It’s well known that aerosol particles from eruptions like Mt. St. Helens can cool temperatures by blocking a small part of the sun’s energy, but a new study suggests that an extreme global warming event about 56 million years ago was caused by massive volcanic C02 emissions.

The research, led by the University of Southampton found evidence that atmospheric C02 doubled within a relatively short period of time, on the geological scale, resulting in a global temperature spike that drove mass extinctions. The eruptions happened during formation of the Atlantic Ocean, according to the study published in the journal Nature.

The warming event, called the Palaeocene-Eocene Thermal Maximum (PETM), has been well-documented in a number of different studies. It lasted about about 150 thousand years and global temperatures increased by at least 5 degrees Celsius, comparable with projections of the warming due to current greenhouse gas emissions.

The PETM  coincided with the formation  large stretches of ocean floor coated in lava, resulting from of a series of huge eruptions. These occurred as Greenland first started separating from north-western Europe, thereby creating the North Atlantic Ocean, the vestiges of which are still continuing in miniature in Iceland today. What has been missing is evidence linking these huge volcanic outpourings to the carbon release and warming that marks the PETM.

Dr Marcus Gutjahr, who led the study while a post-doctoral fellow at the University of Southampton, and is now at the GEOMAR Helmholtz Centre for Ocean Research in Kiel Germany, explained: “In order to identify the source of carbon we first generated a new record of the change in ocean pH (a measure of its acidity) through the PETM, by measuring changes in the balance of isotopes of the element boron in ancient marine fossils called foraminifera.”

The geochemical facilities at the University of Southampton is one of few locations in the world where this kind of work can be carried out. Foraminifera are tiny marine plankton that live near the sea surface and the chemical makeup of their microscopic shells records the environmental conditions of the time when they lived, millions of years ago.

Professor Andy Ridgwell from University of California, Riverside, said, “Ocean pH tells us about the amount of carbon absorbed by ancient seawater, but we can get even more information by also considering changes in the isotopes of carbon, as these provide an indication of its source. When we force a numerical global climate model to take into account both sets of changes, the results point to the large-scale volcanism associated with the opening of the North Atlantic as the primary driver of the PETM.”

The team found that the PETM was associated with a total input of more than 10,000 petagrams of carbon from a predominantly volcanic source. This is a vast amount of carbon – some 30 times larger than all the fossil fuels burned to date and equivalent to all current conventional and unconventional fossil fuel reserves.

In their computer model simulations, it resulted in the concentration of atmospheric CO2 increasing from 800 parts per million to above 2000 ppm. The Earth’s mantle contains more than enough carbon to explain this dramatic rise and it would have been released as magma, pouring from volcanic rifts at the Earth’s surface.

“How the ancient Earth system responded to this carbon injection at the PETM can tell us a great deal about how it might respond in the future to man-made climate change,” said Professor Gavin Foster, from the University of Southampton.

“For instance, we found that Earth’s warming at the PETM was about what we would expect given the CO2 emitted and what we know about the sensitivity of the climate system based on Intergovernmental Panel on Climate Change (IPCC) reports. However, compared with today’s human-made carbon emissions, the rate of carbon addition during the PETM was much slower, by about a factor of 20.”

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