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The Hockey Stick Is Back



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A long post from “Dot Earth” blogger Andrew Revkin on a new study from researchers at Oregon State University and Harvard claiming:

The last century stands out as the anomaly in this record of global temperature since the end of the last ice age…. This research shows that we’ve experienced almost the same range of temperature change since the beginning of the industrial revolution as over the previous 11,000 years of Earth history – but this change happened a lot more quickly.

Revkin writes:

In sum, the work reveals a fresh, and very long, climate “hockey stick.”

The hockey stick climate analogy arose from a variety of studies of the last millennium or two of temperatures in the Northern Hemisphere, Arctic and planet. There’s a general pattern of a sharp warming from the 20th century onward. The shaft of the “stick” has a lot of wiggles and warps and still comes with substantial uncertainty, but the general pattern is well established. The Wikipedia entry is a reasonable starting point for reviewing varied views of this body of science.

This work is complicated, involving lots of statistical methods in extrapolating from scattered sites to a global picture, which means that there’s abundant uncertainty — and that there will be abundant interpretations. 

Revkin includes an e-mail exchange with Berkeley’s Robert Rhode who does caution on reading too much into the certainty of the findings (although he agrees with the broader picture). An excerpt:

Because the analysis method and sparse data used in this study will tend to blur out most century-scale changes, we can’t use the analysis of Marcott et al. to draw any firm conclusions about how unique the rapid changes of the twentieth century are compared to the previous 10,000 years. The 20th century may have had uniquely rapid warming, but we would need higher resolution data to draw that conclusion with any certainty. Similarly, one should be careful in comparing recent decades to early parts of their reconstruction, as one can easily fall into the trap of comparing a single year or decade to what is essentially an average of centuries. To their credit Marcott et al. do recognize and address the issue of suppressed high frequency variability at a number of places in their paper.

And Anthony Watts weighs in with a nice debunking of the “unprecedented” warming:

I had to chuckle at the cacophony of Twitfests going on today over this new study from Marcott et al. I especially liked the Mother Jones headline being Tweeted: “The Scariest Climate Change Graph Just Got Scarier”.

It rather reminds me of some people being fearful of certain religious icons.

Yes, be afraid, very afraid, of that “unprecedented” (there’s that word again in the abstract) 0.7C temperature rise is the message I suppose. While the MSM will trumpet this I’m sure, we’ll get down to finding out just how good the science is. One potential problem is that the pollen data median sampling of 120 years, which is 4x the 30 year climate normals periods used today. That’s pretty low resolution for a study that is focusing on 2000 years and leaves lots of opportunity to miss data. Further, when they say the last 100 years was the warmest (with higher resolution data) they really aren’t comparing similar data sets when the other data has a 120 year median sampling.

Watts’s entire piece here.



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