Jerry Mahlman, a climatologist at GFDL of NOAA, came up with the term "hockey stick graph." Their first graph was for the last 600 years of the northern hemisphere; today's anniversary is for the paper on the last millennium, then Mann and Phil Jones later reconstructed temperatures back to 2000 years BP.
Their work has been attacked like few others in science, but it has held up just fine. No one expected Mann to be the pugilist he turned out to be, who tirelessly fought off everyone at every turn -- auditors, congressman, lawyers and trolls. Sure, it wasn't the last word in temperature reconstruction, but first papers rarely -- for example, the Bohr Model, pre-Einstein papers on Lorentz transformations, the parton model of hadrons, and many many others in science. (I just happen to know the history of physics better than that of any other field.)
Many papers did their part in backing up the HS result by bringing in new data and improving the methodology. Here's a comparison of MBH98 to the PAGES 2k results of a couple years ago, from Stefan Rahmstorf's Facebook page:
One of the particular advancements of MBH was the inclusion of an uncertainty band around the temperatures.
I don't feel like relitigating any of the particulars of a case against the hockey stick, unless someone wants to bring something up in the comments. As I've written before, the hockey stick is required by basic physics, in particular radiative forcing's logarithmic dependence on CO2, which goes back to Arrhenius in 1896. Given that, it's a short argument to the hockey stick, one that can be condensed into a single tweet:
The hockey stick is required by basic physics:
1. temperature change is proportional to forcing change.
2. CO2 forcing change is proportional to log(CO2).
3. CO2 has been increasing exponentially.
=> hockey stick.
(209 characters.) Before the industrial era, the atmospheric CO2 concentration changed little during the Holocene, which implies the flat shaft of the HS. CO2 is increasing exponentially in the industrial era, which implies a linear increase in temperature, which is the blade of the hockey stick.
It'd be far more surprising if there wasn't a hockey stick in the data.
It's been interesting to follow all the twists and turns over the years of the effort to defeat this graph. It would have been interesting to have had social media during some of the big debates in science, such as the debates over the wave or corpuscular view of light, or the probabilistic nature of quantum mechanics, or the establishment of evolution by natural selection. (Here's a good book on some notable feuds in science.) I'd glad all that mischief is over. Science always wins.