11,000 years ago and now

Scientists Find an Abrupt Warm Jog After a Very Long Cooling - NYTimes.com

The Andy Revkin post on last week's science study seems to me to have given too much prevalence to the assessment of Robert Rhode, who suggested that the paper did not have fine enough time scale resolution to rule out past rapid temperature rises of similar magnitude to that of the 20th century that may have come and gone within the space of a few centuries.

Co-author Shukan gets to make a rebuttal in the comments thread that there is pretty good reason to not believe such changes happened, and he also makes the point in the video that, with the known effects of increased CO2, there is no reason to think the present rise is going to go down.  However, these responses are something you have to dig up in the thread, and (as others have claimed) Revkin's desire for balance sometimes ends up giving a false impression.

The Science article in question was pretty well summarised here.  The thing that surprised me was that warming periods over the past 11,000 years did match pretty well with orbital changes that would have increased sun in the north:

Marcott said that one of the natural factors affecting global temperatures over the past 11,300 years is gradual change in the distribution of solar insolation associated with Earth's position relative to the sun.

"During the warmest period of the Holocene, the Earth was positioned such that Northern Hemisphere summers warmed more," Marcott said. "As the Earth's orientation changed, Northern Hemisphere summers became cooler, and we should now be near the bottom of this long-term cooling trend -- but obviously, we are not."

 That's the biggest significance of the paper, it seems to me.

But I should note that Revkin's post on the matter does redeem itself by including this response by Richard Alley, which makes some very important points which climate change fake skeptics do not usually appreciate:

I think it is worth remembering a few things for how this fits into the bigger picture. Whether the past was naturally warmer or cooler than recently, and whether the changes were faster or slower than recently, are of great interest to climate scientists in learning how the climate system works, including the strength of feedbacks. But existence of a warmer climate in the past doesn’t mean that the current warming is natural, any more than the existence of natural fires rules out arson in some recent warehouse blaze. And, existence of a warmer climate in the past also doesn’t mean that we’ll like a warmer climate in the future. Nature has made places and times colder, and warmer, than most people like. Our high assessed confidence that the recent warming is mostly human-driven, and that the costs will become large if the warming becomes large, do not primarily rest on how much warmer or colder today is than some particular time in the past, or even on how fast the recent changes are relative to those in the past.

Furthermore, because the feedbacks in the climate system often respond similarly to warming with different causes (warmer air will tend to melt more snow and ice, and to pick up more greenhouse-gas water vapor from the vast ocean, whether the warmth came from rising CO2 or increasing solar output or alien ray guns or a giant hair dryer), data showing larger climate changes in the past in response to some estimated forcing actually increase the concerns about future warming. If, for example, scientists had somehow underestimated the climate change between Medieval times and the Little Ice Age, or other natural climate changes, without corresponding errors in the estimated size of the causes of the changes, that would suggest stronger amplifying feedbacks and larger future warming from rising greenhouse gases than originally estimated. Any increase in our estimate of the natural climate responses to past forcings points to a more variable future path with larger average changes.

A similar point was made about the Schmitter paper last year - the paper suggested a lower range for climate sensitivity, but another result was that it meant that relatively small temperature changes can have huge impact on large parts of the Earth.