Reply #14

The IPCC says this:

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-projections-of.html

Now a reduction of 315 GtC doesn't sound undoable, does it? The problem is, the 1415 number is apparently the average of all the IPCC models, and only one of them (the Big Kahuna, A1FI) bears any resemblance to what's actually happening outside your house. Even under generous assumptions, we're on track to put out almost twice that much - 2500 GtC - over the 21st century. That's definitely a PETM-class event - PETM may have been triggered by a release of ~3000 GtC.

In fact, if we stay on our current trend (which matches or exceeds the IPCC A1FI scenario) we'll have blown our entire 1100 GtC budget in another 40-50 years.

And of course, that's just to keep the atmosphere down to 1000 ppm in 2100. If we burn everything it looks like we will on the current trend, that would mean soaring past 1500 ppm. That's well into PETM territory.

Can we stop using virtually all carbon-based fuels by 2050? No? Well, the price is PETM II.

This is worth reading, both on the subject of PETM and also why the climate feedback from CO2 is likely understated by a factor of 2 in the current IPCC documents:
http://www.realclimate.org/index.php/archives/2009/08/petm-weirdness/