If tree rings are reliable gauges of temperature why don’t we use them today

Mark Steyn explains Michael Mann’s infamous and thoroughly discredited “hockey stick” in simply terms. Basically it is a fraud and junk science, but the warmists out there still cling to their beliefs despite mounting evidence to the contrary…who are the deniers now?

First, the “hockey stick” graph is so called because it divides neatly into two parts: a long flat “handle” for the millennium before 1900 followed by a 20th century “blade” that shoots straight up. The takeaway – the one that Mann, Al Gore and the IPCC marketed to such effect – is that the earth was hotter in the late 20th century than at any time in the previous millennium.

But the science underpinning the graph is also made up of two elements: actual recorded temperatures, and “proxies” – or temperatures derived from the study of tree rings. That’s because your average medieval peasant village did not have a weather station, and neither Daniel Gabriel Fahrenheit nor Anders Celsius had yet been born.

So what matters is how these two elements – real temperatures and proxies – are “spliced” together. If, for example, the hockey stick simply used tree-rings for the flat handle and temperature readings for the vertical blade, it would perhaps be a bit too crude even for the Big Climate alarmists.

On the other hand, that in turn raises a more obvious question: If tree rings are such a reliable guide to temperatures in the 11th century, and the 13th century, and the 16th century, surely they’re also accurate for the 20th century. So why not just do a straight tree-ring graph of the last millennium? ?

Yes that is a good point…why not use tree rings now as well to see if it continues instead of munging data?

Ah, well. Because that doesn’t tell the story that Mann & Co wanted to sell, and certainly doesn’t make a hockey stick. From the Forties on, the tree rings head south. So, for Mann, the actual temperatures become more useful than the proxies. Steven Goddard distills all this in?a couple of very clear graphs:

Mann deleted the later part of Briffa’s trees, because it didn’t match GISS temperatures.

As ugly as this was, it is worse than it seems. Briffa’s trees did match Hansen, 1981.

“Hansen” is James Hansen, head of NASA’s Goddard Institute. And his 1981 graph of 20th century temperature shows the “global cooling” period from the Forties to the Seventies, when it starts heading up again. The tree rings match mid-20th-century “global cooling” perfectly. Unfortunately for them, since then Hansen & Co have been airbrushing “global cooling” out of the record like a disappeared Politburo comrade. The Climategate emails read awfully like chaps who’ve decided on the result and are just having a wee spot of bother forcing the science to comply with it:

So, if we could reduce the ocean blip by, say, 0.15 degC, then this would be significant for the global mean — but we’d still have to explain the land blip.

At the precise moment when the tree-ring proxies and actual temperatures are in near perfect agreement on a decades-long cooling trend, Mann dumps the tree rings and moves to “observed temperatures” – which have been conveniently revised upward from when they were originally observed. As Steven Goddard says:

In order to create the hockey stick cheat, they had to do the GISS data tampering cheat first. The entire basis of the hockey stick is junk science.

The tree rings are supposedly reliable in the pre-thermometer era. They remain reliable in the age of thermometers as long as both the thermometer and the tree ring are going up. If the thermometer’s going up but the tree ring’s going down, then it’s the thermometer that’s accurate and the tree ring that’s junk. And, if both the thermometer and the tree ring are going down, then neither is accurate and we need to goose the thermometer a little.