The New Hockey Stick

by Wendy McElroy

The latest foofaraw in the global-warming scene is the "Marcott et. al." paper (“A Reconstruction of Regional and Global Temperature for the Past 11,300 Years” by Marcott, Shakun, Clark, and Mix). The media are trumpeting variously that the Earth is "warmer than in most of the past 11,300 years", "a heat spike like this has never happened before", or that "temperatures are rising faster today" or are more volatile than ever before.

Hold on a minute. They're using data samples 120 years apart (median sampling interval), before smoothing. Their smoothing of the data seems to reduce the resolution to 400 years. You simply can't conclude that there was never a 50- or 100- year spike in temperatures, with data that coarse!

The scary graph being bandied about uses "Michael's Little Helper" -- they splice instrumental records for the last 150 years onto the chart. On the 13,000 year graph, the roughly 1-degree rise in the last 100 years looks like an upward spike. As a commenter at DotEarth observed,

[T]hey take these proxies that go back thousands of years and are smoothed to show an average and then tack on our recent temperatures. This is akin to showing our average temperature graphs for the year and then adding our daily temperatures for the last month to show the volatility of our recent climate.

Even using the "smoothed" data, it seems that some 3,100 of the last 11,300 years were warmer than today, and current temperatures are "about average for the Holocene" era. So much for today's temperatures being "unprecedented."

But wait, there's more:

1. The Marcott et. al. reconstruction differs significantly from other, established temperature data for the past 10,000 years -- data that shows warmer temperatures in prehistoric times.

2. The reconstruction averages 73 temperature proxies which are all over the map, numerically speaking. Some of the proxies show a rising trend; others are falling. Some show warming followed by cooling, others cooling followed by warming. Averaging this mish-mash gives, essentially, nothing -- the "handle" of the new hockey stick.

3. It has been pointed out that 80% of the source data is for marine temperatures, so splicing on a land temperature record will show an abrupt change.

4. Steve McIntyre is already finding likely errors in the data. (I do commend Marcott et.al. for releasing their data, if not their computational methods.)

5. Marcott et. al. show the recent warming as starting 100 years ago, before the widespread (post-WW2) use of fossil fuels.

I find myself thinking that this paper was rushed to publication to make the March 15 deadline for inclusion in the next IPCC report...and, conveniently, after the deadline for comments on that report. (Yes, the IPCC allows new papers to be included after the review process is over.) So be prepared for a deluge of breathless "unprecedented temperature rise" claims after that report is released. But the fact is, the Marcott report does not support any such conclusion.

WendyMcElroy.com