Research Suggests Large Mammals Influenced Global Climate

Mammoth exhibit at a museum
Mammoth exhibit at a museum. The rapid decline of mammoths and other megafauna after humans spread across the New World may explain a bone-chilling plunge in global temperatures some 12,800 years ago, researchers reported Sunday.

( -- More than 13,000 years ago, millions of large mammals such as mammoths, mastodon, shrub-ox, bison, ground sloths and camels roamed the Americas and may have had profound influences on the environment according to research in a paper titled, “Methane Emissions from Extinct Megafauna” released in the publication Nature Geosciences Sunday.

The extinction of these large herbivores, which also include horses, llamas and stag moose in addition to the giant wooly mammoth, probably led to an abrupt decrease in methane emissions and atmospheric concentrations of the gas with potential implications for climate change says Dr. Felisa Smith, Associate Professor of Biology at the University of New Mexico.

The research also involved Dr. Scott Elliott from the Climate, Ocean, Sea Ice Modeling Team at the Los Alamos National Laboratory and Dr. Kathleen Lyons in the Department of Paleobiology at the National Museum of Natural History at the Smithsonian Institution.

Approximately 13,400 years ago, the Americas supported a mammal fauna that was richer than that of Africa today explained Smith. “Around 11,500 years ago and within 1,000 years of the arrival of humans in the New World, 80 percent of these large-bodied mammals were extinct,” said Smith in the paper.

“This is arguably the first detectable influence of humans on the environment going back 13,400 years to when humans first got to the continent,” said Smith. “I think that it’s intriguing because there are a lot of ramifications. Potentially, if the decrease in methane, which is synchronous with this ice spell, was actually the cause, then humans contributed to the Younger Dryas cold episode.”

Herbivores produce methane as a by-product of cellulolytic-microbial fermentation during the digestive process. Enteric emission occurs when methane (CH4) is produced in the rumen as microbial fermentation takes place; most of this is released as burps. Past studies have shown that domestic livestock are an important contributor to greenhouse gas concentrations and can represent ~20 percent of annual emissions. The study says that this influence may have been greater in the Pleistocene epoch when methane concentrations were considerably lower.

The researchers looked at 114 different herbivorous species that were extirpated from the Americas at the end of the Pleistocene epoch. Using ice cores to determine the amount of methane during the onset of the Younger Dryas cooling period, they found the extinction of megafauna closely coincides with an abrupt drop in atmospheric methane concentration.

“If you look at the ice cores, which record things like methane, you see this huge drop in methane that perfectly coincides with when humans arrived on the continent,” said Smith. “We looked at all the other drops in methane over the last million years and this one is quite different. It happens about 2-40 times more rapidly than the others.”

Armed with that information, the researchers then decided to try and determine how much methane was produced by these species. They came up with an estimate of the number of animals and then an estimate of how much methane those animals actually produced. Other animals such as elephant, giraffes and hippos have been studied by putting a gas mask type of apparatus on them to determine how much methane they produce in a day.

“We were able to come up with an estimate, which turns out to be about 10 teragrams. This is really pretty enormous,” said Smith. “When you bracket it, at the very minimum, the demise of all these animals explains 12 percent of the decrease in methane seen at this time. At the maximum, it explains the entire decrease. This suggests that the extinction of megafauna by humans caused a detectable impact on the environment long before the development of agriculture and the industrial age.”

Ice core records from Greenland suggest the methane concentration change associated with a 1 degree Celsius temperature shift ranges from 10 to 30 parts per billion by volume with a long term mean of about 20 ppbv. A drop of 185 to 245 ppbv methane drop observed at the Younger Dryas stadial is associated with a temperature shift of 9 to 12 degrees Celsius. The calculations suggest that decreased methane emissions caused by the extinction of New World megafauna could have played a role in the Younger Dryas cooling event.

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Citation: Research Suggests Large Mammals Influenced Global Climate (2010, May 23) retrieved 16 September 2019 from
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May 23, 2010
Yup...Blame humanity for everything....when are you preservationists going to just die out?

May 23, 2010
"from both ends of their digestive tracks."

If the grammar is this bad, the content is suspect.

The word is tracts, for crying out loud!

May 23, 2010
I don't buy this for a New York minute. It is based on too many assumptions and is a thesis tainted by the prevailing climate change hysteria mentality.

May 23, 2010
I thought it was the meteor strike on a northern hemisphere glacier that caused this.
"Evidence unearthed at more than two dozen sites across North America suggests that an extraterrestrial object exploded in Earth's atmosphere above Canada about 12,900 years ago, just as the climate was warming at the end of the last ice age. "

There have been several studies debunking the Lesser Dryas impact event. Google Holocene Impact Working Group.

May 24, 2010
Well one thing is sure if the human rise would suddenly die the global temperature would certainly drop also.
(assuming we didn't blow up ourselves)

May 24, 2010
Junk science built on the foundation of junk science results in questionable findings. But as long as the faux scientists continue to receive research grants, this nonsense will continue.

Global warming is a lie. Attempting to build theories on this lie simply reveals the collective ignorance that exists within the scientific community.

May 24, 2010
Well, if methane were a strong greenhouse gas, and it is, and a continent's worth of large land animals died off, and there was nothing to replace the lost methane . . .

And I'm not talking about the mega-fauna die off. What I'm referring to happened much more recently, within the last 200 years. The American Bison (buffalo) once ranged from Atlantic to Pacific, Gulf of Mexico to north of the Great Lakes. More bison than there are cows today. A sea of bison, gone. All that methane, gone. And the pooftas say we're warming . . . with all that missing methane.

Good day

May 24, 2010
This comment has been removed by a moderator.

May 24, 2010
While these events are likely related, the cause and effect could be constructed in many ways. If humans caused the last ice age by killing the mammoths in North America it started with the Earth warmer, sea levels higher and no land bridge to Alaska. Those events don't seem to fit well chronologically. I can't believe that the tribes coming across the land bridge killed off all the Megafauna in North America in just a few or perhaps several hundred years. I also agree with the previous point about the Bison. So sorry I don't buy the presented theory. Possible, OK, probable,...ahhhh no.

May 24, 2010
The entire history of the earth is extinction after extinction. Why do we assume that will stop just because we are now aware of it?

May 24, 2010

And I'm not talking about the mega-fauna die off. What I'm referring to happened much more recently, within the last 200 years. The American Bison (buffalo) once ranged from Atlantic to Pacific, Gulf of Mexico to north of the Great Lakes. More bison than there are cows today. A sea of bison, gone. All that methane, gone. And the pooftas say we're warming . . . with all that missing methane.

That's an insightful idea. But you can't just cherry pick your sources and sinks of greenhouse gases to get the result you want. What about increased methane release due to human landfills, or fossil fuel extraction? Also, please cite your evidence that there were more bison than there are cows today.

May 24, 2010
When they say "megafauna" does anyone else get a picture of an overly large Mr. Tumnus?...

May 24, 2010
The megafaunal extinction is the earliest catastrophic event attributed to human activity," the study concluded.

Or could be its really hard for a 6 to 8 ton animal to find food in an ice age....

May 31, 2010
I suppose they were driving mammoth SUV'S.

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