From the BBC:
What's really significant, though, is that the amount of carbon dioxide in the atmosphere was very similar [in the Pliocene] to what it is today - at around 400 CO2 molecules for every million molecules of air.
Indeed, the Pliocene was the last time in Earth history that the air carried this same concentration of the greenhouse gas. And it tells you where we're heading if we don't get serious about addressing the climate problem, cautions Prof Martin Siegert from the Grantham Institute at Imperial College London.
Temperatures may currently be lower than in the Pliocene, but that's only because there is a lag in the system, he says. "If you put your oven on at home and set it to 200C, the temperature doesn't get to that level immediately; it takes a bit of time," he told reporters.
"And it's the same with Earth's climate. If you ratchet up the level of CO2 at 400 parts per million (ppm), it won't suddenly get to an equilibrium overnight. It will take maybe 300 years or something. So, the question to us is: what is the equilibrium state; what is Earth's climate going to look like with 400ppm, all things being settled?"
The IPCC report tried - unsuccessfully, if you read it carefully - to explain that increasing CO2 levels from 0.03% to 0.04% would increase temperatures, because ever so slightly more infra-red will be reflected back to the earth's surface.
How quickly would we expect this to happen? It is warmer at night when it's cloudy than when the sky is clear, if the cloud cover blows away, you notice the drop within minutes.
So if, hypothetically, C02 levels were to jump from 0.04% to to 0.05% overnight and this actually increased temperatures, you might not expect any related increase in temperatures to happen within minutes or hours, but perhaps within days, or months or even a whole year.
"Three centuries" is taking the piss.
Debate Magazine
