In 1998 by Michael E. Mann and some colleagues used various tricks to take out past warm periods and defraud the gullible into thinking this is the warmest period in recent history. You could put just about any data into his "algorithm" and it would come out looking like a hockey stick. But since it made it appear like the Earth was getting lots warmer than at any time in the past (and reaching a "tipping point"), propagandists like the IPCC and Al Gore used this to scare-monger around 2000. It was thoroughly debunked by many folks (including real Scientist Tim Ball), and Michael Mann sued Ball for defamation (the crime of telling the truth). Even in the hyper-liberal courts of Canada, Mann lost and had to pay court fees, because he wouldn't show his data like he was a real scientist. And even the far left and completely polemic IPCC pulled Mann's Hockey-stick from subsequent reports, because it made them look bad.
Parts of the fraud:
|Different Measurements - One of the many flaws of Mann is they shifted between temperature proxies which do a low pass filtering and averaging function (de-noising) with direct measurements by a different scale that do not do that, and they fail to call that out. That's scientific fraud. I ask people:
|Tree Ring Proxies - They idiotically overweighted tree ring data to mislead people. And not all tree ring data, but one in particular (Bristlecone pines), despite the author of the tree-ring research warning specifically that this was more indicative of precipitation than climate and NOT to use it as a Climate Proxy which is exactly what Mann did. The Mann Hockeystick smoothed out the the historical climate spikes and valleys, by mixing in historical droughts. But people that never read deeper than the headlines, don't realize how bad that piece of "science" was.|
|IPCC stopped using it - The IPPC dropped using Mann in their reports because it was too bad of science, even for them. And that says a lot.|
|Steven Goddard showed they doctored the data - This was has never been convincingly refuted... they just did new versions so that only the old version were "debunked"... yet they used the same doctored data.|
If you want a deeper dive into the Climate record (and CO2) you can read:
If you can't answer/address these points, then you're not up for a fact based discussion, and if you could, you'd win the Nobel prize: