One of my passions in life is climate science and research, and I am a strong defender of the science proving anthropogenic global warming. The UN Intergovernmental Panel on Climate Change has long attempted to bring to the forefront the scientific facts about humanities effects on the environment. Naturally, there have been those who have set out to simply ignore or discredit them at every turn.

One of the focuses of their attacks has been what some call the “notorious hockey stick” graph. The graph shows a fluctuating temperature variation over the past 2000 years (including the Medieval Warming period), with a marked spike at the end; in other words, a flat (for a given value of flat, see graph below) line and a curve at the end, similar to a hockey stick. You will have seen the graph if you’ve watched Al Gore’s An Inconvenient Truth.

Now, a new report in the Proceedings of the National Academy of Sciences entitled “Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia” has once again validated the science behind the hockey stick graph.

As mentioned, there are those out there willing to discredit anything if given half a chance. The hockey stick graph has taken a lot of flak since its arrival on the scene. Just the other day, Christopher Booker at the Telegraph used the hockey stick graph – a graph he believed to be false – as a means to undermine all that the IPCC has done. This new report denies Booker his claims, and holds up the IPCC’s belief in man-made global warming.

Using a new set of proxy data for decadal-to-centennial climate changes, Michael E. Mann and colleagues reconstructed surface temperature at hemispheric and global scale for much of the last 2,000 years. Their new set of proxies, in addition recently updated instrumental data, both of which had been thoroughly tested and validated, once again backed up the hockey stick.

“Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context,” the authors write. “Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats.”

In other words, the recent spike in warming – as detected in tree-rings, marine sediment, speleothem, lacustrine, ice core, coral, and historical documentary series, collected from across the world (see opening image) – should not have been there, based on previous patterns over the past 2000 human-filled-years.

One interesting note is that in acknowledging the scientific validity of the Medieval Warming, they add that the current warming has well surpassed that period’s warm spike. It’s almost not necessary, but there goes another nail into the coffin for those out to discredit man-made global warming.

Read the full report via PNAS here (PDF)

More on Man-Made Global Warming at the GO Network

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