Thread by @marcelcrok

"Long tree ring chronologies have negligible millennial-scale variance – one more reason to distrust the temperature reconstructions of PAGES2K and IPCC."
From a post by good old @ClimateAudit. Time to read it now @IPCC_CH decided to publish a brand 'new' (aka old) hockey stick.

Steve's post is based on Esper et al 2012 en the key figure from that paper was hidden in the Supplementary information:
climateaudit.org/2021/03/02/mil…

The paper looks at high latitude climate proxies in Scandinavia and Russia. In grey tree rings, showing no long term trend whatsoever. However, in blue (glacier in Norway) and green (tree line in Russia) a longterm decline in the past thousands of years becomes visible.

In red and orange two simulations of the summer temperature in these regions. What we are seeing here is the to be expected longterm decline in summer temperatures as a result of declining solar insolation (milankovitch). Here a rough impression:

Look at the vertical scale of this graph. The changes in summer insolation at 65 degrees North are slow but over the course of millennia much bigger than the (global) forcing of GHGs since 1750 (2.72 W/m2 according to AR6).

Another really interesting figure in Steve's post is from Vinther et al 2009 based on Greenland ice cores.

Read Steve's post why Vinther thinks that Renland (a peninsula on the east coast) probably provides a more reliable proxy of holocene temperature than the much more often used GISP2 ice core at the top of Greenland.

The new IPCC AR6 hockeystick - like most of the hockeysticks in the past - probably relies heavily on tree rings which as Esper showed don't show the longterm milankovitch signal that you would expect at high latitudes.

With the grey bar at the left AR6 even claims that current temperatures are higher than those of the holocene thermal optimum. Simply said: IPCC flattens the past to highlight that current warming is rapid and unprecdented.

My career as a climate journalist started with a very long article on the hockeystick in 2005, based on the work of @ClimateAudit and @RossMcKitrick. The article was awarded with a prize and can be read here:
climategate.nl/wp-content/upl…

As insiders know, the hockeystick saga played a key role in the climategate emails. @ClimateAudit was the 'sceptic' most often mentioned in the emails, often in very derogatory language. McIntyre - although he expected some - was truly disappointed by their behaviour.

Everyone was tired of the whole issue and in AR5 the IPCC itself - although it didn't fully left their hockeystick storyline - they didn't promote it either.
Now times have changed again. In AR6 the hockeystick is back in full glory.

In Holland, the claim surrounding the new hockeystick was the opening ("the climate is changing faster than ever") at the 8 o'clock national news.

As this threat attempted to show, these claims are likely flawed. Laregly based on tree rings the IPCC presents a history of the holocene climate that is far too flat, to then claim the current warming is fast and unprecedented.

As Esper concluded in his 2012 paper: "an evaluation of long-term temperature reconstructions, even over the past 7,000 years from across northern Eurasia, demonstrates that TRW-based records fail to show orbital signatures found in low-resolution proxy archives and ...

... climate model simulations. These discrepancies not only reveal that dendrochronological records are limited in preserving millennial scale variance, but also suggest that hemispheric reconstructions, integrating these data, might underestimate natural climate variability."

As @ClimateAudit concluded:
"This conclusion impacts PAGES2K, Mann et al 2008 and all other temperature reconstructions relied upon by IPCC." END
climateaudit.org/2021/03/02/mil…