Thawing Permafrost Attributed to Acute Global Warming in Past
10.04.2012 - Atmosphere & Space, Land & Geology, Ice & Snow, Bi-polar
An international study conducted by researchers from the US, Italy and the UK published in Nature has shown that past thawing of permafrost on Earth and the carbon that was released from it into the atmosphere led to a runaway warming effect.
A change in the Earth’s orbit triggered three massive hypothermals, or massive warming events, on the planet beginning 55 million years ago known as the Paleocene-Eocene Thermal Maximum (PETM). Examining a rock outcrop in Italy that contains evidence of the ancient hypothermals, the team of researchers determined that the warming events lined up with times in the Earth’s orbit in which the planet’s axial tilt was greatest and its orbit was most eccentric, which allowed for more solar radiation to reach the Polar Regions. This allowed permafrost close to the Poles to thaw, which released several trillion tons of carbon into the atmosphere (as the greenhouse gasses carbon dioxide (CO2) and methane (CH4)), leading to a positive feedback loop of accelerated warming.
It had been previously believed that the warming had caused extra methane to be released from methane hydrates (methane dissolved in ice) at the bottom of the sea. However the amount of methane stored in those hydrates, based on estimates of today’s stores of methane hydrates, wouldn’t have been sufficient to create the kind of warming that occurred 55 million years ago. The amount of carbon released from thawing permafrost that is believed to have been around at the time would have been sufficient to create the warming, according to the team of researchers.
The team put together a model that showed a “sweet spot” in the model for melting permafrost: once the threshold is crossed, the rate of warming increases dramatically.
The study suggests that runaway climate change is also a possible scenario for present-day climate change. As anthropogenic greenhouse gas emissions contribute to warming, it will thaw permafrost, releasing even more carbon into the atmosphere.