Michael Mann’s bias on Hockey Sticks

Two major gripes of mine with the “Climate Consensus” are their making unsubstantiated claims from authority, and a total failure to acknowledge when one of their own makes stupid, alarmist comments that contradict the peer-reviewed consensus.

An example is from Professor Michael Mann commenting on his specialist subject of temperature reconstructions of the past for a Skeptical science “97% Consensus” spin-off campaign.

I will break this statement down.

“There are now dozens of hockey sticks and they all come to the same basic conclusion”

His view is that warming is unprecedented, shown by dozens of hockey sticks that replicate his famous graph in the UNIPCC Third Assessment Report of 2001.

Rather than look at the broader picture warming being unprecedented on any time scale1, I will concentrate on this one thousand year period. If a global reconstruction shows a hockey stick, then (without strong reasoned arguments to the contrary) one would expect the vast majority of temperature reconstructions from actual sites by various methods to also show hockey sticks

CO2Science.com, in their Medieval Warm Period Project, have catalogued loads of these reconstructions from all over the world. They split them into two categories – quantitative and qualitative differentials in the average temperature estimates between the peak of the medieval warm period and now.

It would seem to me that Mann is contradicted by the evidence of dozens of studies, but corroborated by only a few. Mann’s statement of dozens of hockey sticks reaching the same basic conclusion ignores the considerable evidence to the contrary.

“The recent warming does appear to be unprecedented as far back as we can go”

Maybe, as Mann and his fellow “scientists” like to claim, that the people behind this website are in “denial” of the science. Maybe they have just cherry-picked a few studies from a much greater number of reconstructions. So let us look at the evidence the SkS team provide. After all, it is they who are running the show. Under their article on the medieval warm period, there is the following graph of more recent climate reconstructions.

It would seem the “Mann EIV” reconstruction in green does not show a hockey stick, but flat (or gently rising) temperatures from 500-1000 AD; falling temperatures to around 1800; then an uptick starting decades before the major rise in CO2 levels post 1945. The twentieth century rise in temperatures appears to be about half the 0.7oC recorded by the thermometers, leading one to suspect that reconstructions understate past fluctuations in temperature as well. The later Ljungqvist reconstructions shows a more pronounced medieval warm period and a much earlier start of the current warming phase, in around 1700. This is in agreement with the Moberg and Hegerl reconstructions. Further the Moberg reconstruction has a small decline in temperatures post 1950.

Even worse, the graphic was from the Pages2K site. On temperature reconstructions of the last two millennia Pages2K state:-

Despite significant progress over the last few decades, we still do not sufficiently understand the precise sequence of changes related to regional climate forcings, internal variability, system feedbacks, and the responses of surface climate, land-cover, and bio- and hydro-sphere.

Furthermore, at the decadal-to-centennial timescale we do not understand how sensitive the climate is to changes in solar activity, frequency of volcanic eruptions, greenhouse gas and aerosol concentration, and land cover.

So Michael Mann’s statement if warming being unprecedented is contradicted by peer-reviewed science. Skeptical Science published this statement when it was falsified by Mann’s own published research and that of others.

“But even if we didn’t have that evidence, we would still know that humans are warming the planet, changing the climate and that represent a threat if we don’t do something about it”

There is no corroborating evidence to the climate models from temperature reconstructions. In fact, empirical data shows that the models may be claiming as human-caused temperature increases that are naturally-caused, but for reasons not fully understood. So the “knowing” must be assumed to be from belief, just as the threat and the ability of the seven billion “us” to counter that threat are beliefs as well.

Kevin Marshall



  1. The emergence from the Younger Dryas cooling period 11,500 years ago was at least 10 times the warming of the past 100 years, and was maybe in a period of less than 300 years. See WUWT article here, or the emerging story on the causes here.
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