The "hockey stick chart" is a fake reconstruction of the global average temperature for the past one thousand years. Hockey stick versus reality at the link below:
http://myweb.wwu.edu/dbunny/pdfs/climategate/The-hockey-stick.pdf
The hockey stick ignored the actual cooling and warming trends found in almost all historical climate reconstructions, by selecting a sub-standard climate proxy that appeared to show a steady global average temperature in the past pne thousand years.
But tree ring data that Mann used reflect changes in rainfall, CO2 levels and temperature -- not only temperature changes.
Even worse, the tree ring data failed to showed global cooling after 1960, so Mann truncated the tree ring data after 1960, and attached real time thermometer data (which includes lots of wild guess "infilling" before 1940), that showed a lot of warming after a long flat temperature trend.
No one was told there were two data sources on the chart.
No one was told the large majority of climate reconstructions did not show a flat temperature trend in the past.
The chart was a lie in more than one way.
Following are some excerpts from Mark Steyn's Motion for a Summary Judgement against the Michael Mann libel suit against him, that has been going on for many years.
Mann has a nasty habit of suing anyone who criticizes his biased "science".
He is obviously a nasty man.
"MANN’S HOCKEY STICK WAR
The Penn State investigation that both Simberg and Steyn wrote about emerged from the public controversy over Mann’s work on what came to be known as the “Hockey Stick” graph.
Mann has long been a lightning rod for criticism.
In 1998 and 1999, Mann and two
colleagues published articles containing a graph that, they claimed, supported sharply increasing worldwide temperatures since 1850.
The graph looked like a hockey stick, with a long flat shaft representing temperatures from the year 1000 to 1850, followed by a sharp upward blade showing a rise.
Because of its vivid visual impact, the graph became much used by those proposing that governments take action to deal with what they saw as the threat of man-made global warming.
The Hockey Stick graph created a “media frenzy,” turned into a “political football,” , and became “a rallying point, and a target, in the subsequent debate over the existence and cause of global warming and what, if anything, should be done about it.”
... Criticisms of the Hockey Stick Abound:
A.W. Montford,
The Hockey Stick Illusion: Global Warming and the Corruption of Science (2009);
A.W. Montford,
“Hide the Decline,” (2012);
Mark Steyn, ed.,
A Disgrace to the Profession
(2015) (collecting criticisms of
Mann and the Hockey Stick by over one hundred respected scientists worldwide)
... “Most scientists dismiss the Hockey Stick.”
It has been called “fraudulent” or a “fraud” at least fifteen times by fellow scientists and others.
By 2006, debate about the Hockey Stick reached such a fevered pitch that the U.S. House of Representatives formed a committee that determined that the Hockey Stick’s findings were “somewhat obscure and incomplete” and found several “criticisms” of the graph “to be valid and compelling.”
The Wall Street Journal published an editorial titled “Hockey Stick Hokum” about the congressional committee’s findings that “Mann’s papers are plagued by basic statistical errors that call his conclusions into doubt.”
Such criticisms of the Hockey Stick multiplied and intensified in 2009
when embarrassing revelations in Mann’s emails and those other climate researchers at the University of East Anglia’s Climatic Research Unit came to light.
In those emails, researchers said the Hockey Stick depended on “Mike’s
Nature trick” — combining actual temperature data with proxy datasets.
The emails also discussed Mann’s deleting post-1960 data from tree ring proxies that showed a decline in temperatures after 1960.
This was done, the emails stated, to “hide the decline” in the post-1960 data.
Mann admitted that public perception, not scientific precision, drove his deletion of the inconvenient data.
So embarrassing were these revelations that the episode soon took on the disparaging title “Climategate.”
Another flood of scientific and media criticism ensued.
Reacting to Climategate, Penn State purported to investigate Mann, but it was a sham.
The Penn State investigation did not consider whether Mann had committed fraud or data manipulation regarding the Hockey Stick.
Penn State’s so-called investigation was so flawed, inadequate, and improper that it quickly prompted justified cries of a “whitewash” and “cover-up.”