Events at the end of the last Ice Age triggered the extinction of mastodons (left), mammoths and other large animals. A new study suggests that they were crowded out of Earth's ecosystem by the energy requirements of the growing biomass of humans and domesticated animals. Art by Raul Martín.

Have you ever considered yourself part of the megafaunal biomass? Anthony Barnosky of the University of California at Berkeley does and he's counted himself, and you, into estimates of the biomass of all large animals and humans living on Earth today and during the past 1 million years.

He has proposed in a paper, published in the Proceedings of the National Academy of Science, that the stage is set for a megafaunal extinction that will make the loss of woolly mammoths, sabertooth cats and other large animals at the end of the last Ice Age seem like a minor blip in the paleontological record.

The biomass of a species leaves an energy footprint on the ecosystem. This makes intuitive sense, but it gained significance for me when Barnosky described what this might have to do with extinctions. The way he looks at the extinction event at the end of the last Ice Age (around 10,000 BC) is that the human population reached a point  where its biomass and associated energy needs overwhelmed the other megafauna (defined as animals over 40 kg or 88 lbs). At that point, Barnosky argues, the planet switched to a "new normal" where humans and their few species of domesticated animals monopolized the ecospace previously occupied by many different wild animals.

This is where it gets interesting. Barnosky's studies show that megafaunal biomass has been about 200 billion kilograms (about 220,000 million tons) for the last million years. As human biomass grew during that time other species gave ground, thus maintaining a balance.

At the end of the last Ice Age (aka. the last major global warming event) pressure on the ecosystem from a  growing human biomass contributed to the collapse of the million-year-old balance. The collapse resulted in Earth's megafaunal biomass dropping to half its previous levels. 

It took until the onset of the industrial revolution for megafaunal biomass to get back to pre-crash levels. But humans and domesticated animals were its major component. Since then, the growth of biomass has surged out of control. The reason is that new energy—primarily from fossil fuels—is being pumped into the system, artificially increasing the carrying capacity of the ecosystem.

Modern megafaunal biomass, seen stretching to the horizon in this picture from India, is seven times the level it has been for the preceding million years. Photo by John Scofield.

Barnosky wonders how long that can continue. Our current megafaunal biomass, comprised of billions of people, sheep, cows, pigs, etc... stands at over 1,540,000 million tons. Some estimates have oil running out in 50 years, natural gas in 200, coal in 2000. Our megafaunal biomass is primed for a megacrash.

Barnosky tries to put a positive spin on things; he's not a doomsayer. But the last line of his abstract is the message we need to take home. He says, "...a near-future biomass crash that will unfavorably impact humans and their domesticates and other species is unavoidable unless alternative energy sources are developed to replace dwindling supplies of fossil fuels."

So, if you needed incentive to get on the alternative energy bandwagon, there it is. If we can manage the transition from fossil fuels to alternatives smoothly so there's no energy lapse, even a temporary one, we can avoid the crash and maybe slow down global warming to boot. Manage it poorly and we get the biomass crash...and we'll still have to develop the alternatives, unless we're one of the megafauna that go extinct.

Barnosky's science may be scary, but this is a great example of why studying the past is important for our future.

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