Megafauna Extinction Due to Climate

jvchamary writes "Most biologists believe that Earth is currently undergoing its sixth mass extinction. The cause? Human activity, either directly (e.g. the Dodo) or indirectly (e.g. the Amazon rainforests). The disappearance 30,000-45,000 years ago of the Australian megafauna, large animals such as the marsupial lion, is often attributed to hunting by Aboriginal settlers. However, recent research in Proceedings of the National Academy of Sciences suggests that it was more likely a shift in climate, rather than hunting, that caused the over-sized organisms to die-out (via Nature and the BBC)."

Comments

Re:So what does that mean for us?

[Anonymous Coward]

civilzation is turning up the thermostat on ol' Mother Earth

No it's not.

Solar Activity Coinciding with Climate Change

[bacon55]

There's a lot of evidence to link large scale climate change with periods of heightend and lowered activity in the Sun.

Taken From "http://www.exploratorium.edu/sunspots/"

From 1645 to 1715, there was a drastically reduced number of sunspots. This period of reduced solar activity, which was first noticed by G. Sporer and was later investigated by E.W. Maunder, is now called the Maunder Minimum. This period of time was also unusually cold on earth, and it has been referred to as the "Little Ice Age." This has led to some speculation that sunspot activity may affect the earth's climate. Similar periods of low solar activity seem to have occurred during the Spoerer Minimum (1420-1530), the Wolf Minimum (1280-1340), and the Oort minimum (1010-1050). Solar astronomers label solar cycles from one minimum to the next, and assign them numbers, starting at one, with the 1755-1766 cycle.

Personally, I've always found it rather arrogant to believe we are the greatest cause of climate change on Earth. Lol, it could be that the Sun is literally causing us to use more energy...but thats taking the butterfly effect a little too literally - maybe.

Re:denying global warming...

[Locke2005]

They don't deny global warming. They deny that global warming is primarily caused by human activity. If the warming trend is in fact part of a natural geological cycle, then sacrificing all our technology tomorrow wouldn't help much, would it? Perhaps what we need is NEW technology to help even out the ice age/warm age cycles.

Personally, I beleive that all the carbon dioxide we've released in the last 100 years must be having some effect.

Re:Bummer...

[Rei]

I forgot to mention another reason why climate clearly isn't the only issue: Holdouts. For several species, there were inaccessable regions which humans didn't discover right away - for example, mammoths on Wrangel Island. While the climate changed around them, they survived just fine. Their mainland bretheren, encountering humans and their side effects, died out.

Re:MegaBeaver

[Neop2Lemus]

The above, you ignant prudes is not flamebait.

ackthpt, however that is pronounced :-p, I'm not sure the beaver was 6' tall, here's a picture of a model one courtesy of the CBC: Castoroides ohioensis. That's the host of the show, Quirks & Quarks beside him.

Re:There goes the neighborhood.

[the phantom]

Because in other parts of the world, the megafauna survived. For intance, in Africa: Elephants, Lions, Giraffes, Rhinos, Hippos, and Gazelles; in Europe: Cows, Deer, and Reindeer; in Asia: Pigs, Sheep, Yaks, and Water Buffalo.

In North America, which is the part of the world that I know best, Mammoths, Mastadons, Giant Armadillos, Giant Beavers, Sabre Tooth Tigers, and numerous other species all went extinct between 11 and 9 kBP (those are radiocarbon years -- I don't recall right off where that calibrates in calendar years -- about 15 kBP, maybe), about the time that a sizeable group of anthropologists think that humans first made it into the New World.

I happen to come from a school of thought that is somewhere in between. There were climate changes at about the time that megafauna went extinct (about 40 kBP in Austrailia, about 11-9 kBP in North America -- both global changes, however there were still megafauna in the Americas after 40 kBP). The climate probably put pressure on the large animals, but I think what finlly killed them off was over hunting. In a more hospitable climate, the animals might have survived. Without humans, the animals might have survived. With both, there was no chance. xander

Re:Bummer...

[Anonymous Coward]

There's problems with all megafauna extinction theories including the disease theory.

While diseases can and do cause total catastrophic extinction, very few do it for a wide variety of species. To wipe out all the megafauna in North and South America for example, would require one hellacious virus such as we've never seen before, or a whole army of super-pestilences (which, while not impossible, would be a whole lot of coincidences).

Super-pests can wipe out species very effectively too, but only within their range. i.e. rats and mosquitos are going to be downright virulent in the lowlands but not so bad in the highlands.

Super-hunters are a fine solution, but they require evidence of the hunters in every place on the continent where extinctions occurred, when it occurred. In the case of America, humans arrived via Alaska, but were not instantaneously causing extinctions in Brazil.

And so on. Yes, these can all be made more possible with the knocking out of specific keystone species (which would be another coincidence, except for the hunting theory, where killing the nonhuman top predator makes sense).

The short answer is we don't know. These are all great theories though. There's probably more.

But tracing any mass extinction to a single cause is going to be damned difficult (and perpetually in contention) unless you have an actual impact crater and a lot of iridium. And even then you get some contention. It's much easier to track the extinction of one species, preferably in the last two hundred years when things were moderately well-documented.