Paleo tagging past climate sensitivity is a classic “half the story” post by Anthony Watts. A new comment in Proceedings of the National Academy of Sciences, “Fossil soils constrain ancient climate sensitivity” basically confirms the conventional estimate of climate sensitivity to increases in CO2 that is the basis for concern about AGW. The authors state “the geologic evidence… is most consistent with long-term, future climate change being more severe than presently anticipated.“

Anthony’s predictable response is to repeat the discredited position that this “still does not address the temperature/CO2 800 year time lag seen in ice core records“. Uh, the historical “800 year lag” thing is understood and irrelevant (the impact of cyclic warming due to of the Earth’s orbital mechanics on the ocean’s dissolved CO2 content) and Anthony knows it; he just hopes you don’t. So what if Al Gore didn’t mention it in his film An Inconvenient Truth? This quote from skepticalscience.com explains the concept [italics mine]:

When the Earth comes out of an ice age, the warming is not initiated by CO2 but by changes in the Earth’s orbit. The warming causes the oceans to give up CO2. The CO2 amplifies the warming and mixes through the atmosphere, spreading warming throughout the planet.

So there are two ways for global warming to occur: an increase in heat input or a decrease in heat loss. Slow “natural” global warming seems linked to increases in heat input that release oceanic CO2, which feeds back on that warming by decreasing heat loss until the natural trigger reverses. Rapid man-made global warming lacks the natural cyclic trigger; adding CO2 into the atmosphere decreases heat loss via the greenhouse effect and this warming will cause the oceans to release additional CO2. The distinction is real and significant, no matter how the denialists try to spin away from it.

I think Anthony would have been better served to keep quiet about this one, much as he likes to try to “position” facts for his credulous audience… By the way, the global warming we are experiencing shouldn’t happen for roughly 23,000 years based on Milankovitch cycle estimates.