Ice cores from Greenland suggest that the rapid decline of mammoths and other megafauna may explain a plunge in global temperatures some 12,800 years ago.
Credit: U.S. National Science Foundation
PARIS: The rapid decline of mammoths and other megafauna after humans spread across the Americas may explain a bone-chilling plunge in global temperatures some 12,800 years ago, researchers report.
The 100-odd species of grass-eating giants that once crowded the North American landscape released huge quantities of methane - from both ends of their digestive tracks.
As a heat-trapping greenhouse gas, methane is 30 times more potent than carbon dioxide (CO2).
It was not enough to trigger runaway global warming. But when all that gaseous output suddenly tapered off, it caused or at least contributed to a prolonged freeze known as the Younger Dryas cold event, they argue.
The Anthropocene
If so, the 'Anthropocene epoch' - the era of major human impacts on Earth's climate system - began not with the Industrial Revolution in the 1800s, but the large-scale influx of two-legged predators to the Americas more than 13,000 years earlier.
Calculations by a trio or researchers led by Felisa Smith of the University of New Mexico, published in the British journal, Nature, show how all the pieces of this previously unsolved puzzle might fit together.
Extrapolating from data on cows and other modern-day ruminants, the scientists estimated the total methane output of pre-historic megafauna at nearly 10 trillion grams per year.
Deep chill
At the same time, ice-core samples reveal that an abrupt drop in atmospheric methane levels of 180 parts per billion by volume (ppbv) coincides with both, the virtual extinction of these gas-gushing herbivores and the onset of the deep chill that followed.
Greenland ice cores from other periods show that a reduction in methane levels of 20 ppbv corresponds to a reduction in temperature of roughly 1 degrees Celsius. That would add up to a decrease of 9 to 12 C, a near-perfect match with the Younger Dryas cold snap.
"We find that the loss of megafauna could explain 12.5 to 100 percent of the atmospheric decrease in methane observed," the researchers said.
Confluence of factors
The theory is bolstered by the fact that the plunge in concentration was two-to-four times faster than the five other largest methane drops during the last 500,000 years, suggesting a unique confluence of factors.
"The megafaunal extinction is the earliest catastrophic event attributed to human activity," the study concluded.
"We thus propose that the onset of the 'Anthropocene' [epoch] should be recalibrated to 13,400 years before present, coincident with the first large-scale migrations of humans into the Americas."
Amounts
Not that I really want to 'diss' this article (it certainly seems important, although the period of the younger Dryas is merely a short chill at the end of a much longer glacial) - but 10 trillion grams of methane is only 10,000 tons - barely a blip in the scale of today's emissions.
More than 10,000 tons?
Depending on who you ask a trillion is either a million million or it is a million million million. (Short scale or long scale).
So in short scale a trillion grams is a million tons of methane (there are one million grams in a ton which in metric is actually "tonne" but the two are similar).
And in long scale it is a million million tons of methane.
Look "trillion" up in Wikipedia.
Where did you get 10,000 tons from?
Megafauna methane
It appears a safe bet that this calculation of methane production from megafauna is gross production and does not account for the uptake of methane by methanotrophic bacteria living in the soils on which these animals lived. Animal physiologists tend to not have the deep microbiology background to know that these bacteria even exist and so publish claims about animal output as if that is the same thing as actual net release to the atmosphere. The same nonsense is being promoted about todays farm livestock.
Last year a paper reported the discovery of aerobic marine bacteria that release methane as a by-product of their metabolism. Previously it was believed only anaerobic archaea could produce methane. Obviously a slight change in growing conditions multiplied over the vast volume of the oceans would be a more likely account for changes in methane ppbv.
We also now know about the Al Gore trick of claiming global temperature changes to be caused by CO2 ppm changes as recorded in ice-cores by using data from time points separated by long time periods such as up to 100,000 years. When the data from ice-cores was gathered from short time periods (a few thousand years), low and behold, tempatures changed and THEN the gas concentrations changed.
Michael Russell, New Zealand
Hypothesis nothing but hot air
There is ample proof that North America was thick with other gassy ungulates - untold numbers of bison, elk, deer, caribou, moose and a variety of sheep did their part to ensure that large quantities of CH4 were produced while the relative few "megafauna" perished.
6th extinction
Ok, so this article and the one I just read about "human induced" cause for something called the 6th extinction event are just more junk science with end of the world writings designed to gain power and money for "scientists" and promote a godless world. I think it good that I am approching the twilight of my life as I am really sick and tired of seeing this, paying taxes, being broke, told that I am stupid because I do not think like a liberal, and used by politicians who would be nothing more than warlords if chaos broke out due to their personal need to be in charge.