A recent article in New Scientist asks, "Did early hunters cause climate change?"
"When hunters arrived in North America and drove mammoths and other large mammals to extinction, the methane balance of the atmosphere could have changed as a result, triggering the global cool spell that followed. The large grazing animals would have produced copious amounts of methane, a potent greenhouse gas, from their digestive systems. They vanished about 13,000 years ago."
The skeptics take issue with the paper for a few reasons.
- Temperature is highly correlated with methane, including during this period, and changes in temperatures could well be causing changes in methane levels (which fluctuate naturally). Since most methane comes from fermentation in wetlands, temperature changes could slow or quicken the fermentation process.
- The methane drop is quickly followed by an even higher rise in methane. It's not as if the megafauna came back to life, though it's possible that other factors caused the rise.
- Using the IPCC's own assumptions about methane forcing and the methane estimates in the paper, the estimated global temperature change from the mass extinction is 0.08 degrees C. Yeah, so hardly anything.
Read the whole broadside here. Note: the tone is less formal than an academic journal, but they open source their methods so anyone can check it.
(Thanks to @melbournian for the New Scientist article.)
