Earth Blows Hot and Cold

The Big Freeze

Humans likely caused the extinction of megafauna species in the Americas.

Around 12,000 years ago, the Earth spun into The Big Freeze, a (geologically) brief cold snap known as the Younger Dryas event. Glaciers returned to parts of the Northern Hemisphere and humans who were around then probably shivered quite a bit.

The Clovis people in North American, the first paleo-Indian inhabitants that made distinctive bone and ivory tools, took a population nosedive. What caused The Big Freeze?

The prevailing theory is a shutdown of the ocean conveyor belt caused by a rapid influx of fresh water from the melting of an immense glacial lake — Lake Agassiz — the used to cover much of Canada. Comets are also speculated culprits. But a New Mexico team of researchers is looking into an unusual contributing factor — a steep decline in large animal flatulence.

It’s no secret that humans probably caused the extinction of megafauna species in the New World, which used to be richer than modern day Africa. Within a thousand years of human arrival, species like mammoth, camelids (the ancestors of camels) and giant ground sloths were destined as museum pieces.

Image Credit: Aaron L. Gronstal

In a paper published in Nature Geoscience this month, Methane Emissions from Extinct Megafauna, Felisa Smith of the biology department at the University of New Mexico and colleagues, attribute a steep drop in atmosphere methane levels to the disappearance of these behemoths.

If domestic livestock contributes about 20 percent of global methane emissions today, then mammoths and the like must have had powerful bowels. Since Pleistocene methane levels were considerably lower than today, these megaherbivores might have had a larger influence on global methane levels.

The researchers went about estimating how much gas an 8-ton herbivore would emit. They examined 114 herbivores that went extinct at the end of the Pleistocene epoch, adjusting for body size and other traits to compute overall methane production from these beasts.

Their calculation suggested that the Pleistocene extinction dropped methane levels by about 9.6 teragrams (or megatons), making the mass extinction responsible for somewhere between a 12.5 to 100 percent of overall methane decline. That’s a big range, but the researchers go on to point out a unique attribute of global methane decline at that time. It happened quite quickly, two to four times faster than any other time interval, “which suggests that novel mechanisms may be responsible.”

Novel, indeed. The overall drop in methane, a potent greenhouse gas, during that epoch equated to temperatures 16 to 22 degrees Fahrenheit cooler. The researchers write:

Greece has been hit with massive wildfires in recent years. Photo courtsey of NASA, 2009

The attribution and magnitude of the Younger Dryas temperature shift, however, remain unclear. Nevertheless, our calculations suggest that decreased methane emissions caused by the extinction of the New World megafauna could have played a role in the Younger Dryas cooling event.

They go on to say that the megafauna extinction may have been “the earliest catastrophic event attributed to human activities.” It may even be the first time humans altered the climate.

Sizzling Hot

Massive wildfires that cause untold destruction of life and habitat are becoming a feature of modern climate change. A mere 1.8 degree jump in temperature is predicted to equal a 40 percent increase in lightening, the main ignition source of natural fires. We already get some 8 million strikes a day under modern atmospheric conditions. It’s becoming sizzling hot here on Earth.

New research into the past is backing up modern day observations. In a paper published in May in Nature Geoscience, researchers at University College Dublin and colleagues tracked down climate and fire conditions from 200 million years ago during a major environmental transition period in Earth’s history – the Triassic-Jurassic boundary.

Foothills of NASA’s Jet Propulsion Lab in Pasadena, California, 2009. Courtesy of Brent Buffington, JPL

During this period, massive volcanism broke apart the super-continent of Pangaea and spiked CO2 levels from 600 to more than 2,100 parts per million by volume. For comparison, Earth’s current CO2 concentration is about 391 ppmv, an all time high for recent history. The resulting mass extinction gave way to our most imaginative period in paleo-history – the age of large dinosaurs. Common, too, emerged the conifers – woody plants with thin needles and seed-bearing cones.

What the researchers found was that as CO2 spiked, so did the number of fires. They looked at about 15,500 fossil charcoal particles from this time period in East Greenland and discovered a five-fold increase in charcoal abundance during peak CO2 levels. The vegetation also appeared to be changing. As temperatures rose, broad-leafed plants died off and were replaced by narrow-leafed varieties.

Coutesy of NOAA photo library

These narrow-leafers were able to withstand higher temperatures, but were also more prone to burn because they contained less moisture. Just think of the last campfire you built – what do you throw in to really get it going? Pine needles.

The researchers suspect a positive feedback loop emerged. As more lightening struck, the ignition rates and spread of wildfires increased due to the burn-prone vegetation, which then released more carbon back into the atmosphere and exacerbated the conditions even more.

What this says about modern day climate change is informative. All that fiery turmoil during the Triassic-Jurassic boundary happened with a temperature change of about 7 degrees Fahrenheit.