​You may have already heard of the 1999 hockey stick created by Michael Mann, Malcolm Hughes, and Raymond Bradley. It’s a frequent skeptic talking point, and was involved in a whole scandal called climategate that rocked the scientific world. Eventually however it was validated by dozens of independent studies, and its conclusions accepted – the world is currently undergoing warming the likes of which humans have never seen before. Last month however, the hockey stick got an amazing upgrade. A new paper by Osman et al reconstructed the past 24,000 years of climate using new techniques, and gave us new insights into just how unprecedented anthropogenic global warming really is.

NOTES/REFERENCES
(1) https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1999GL900070
(2) This is a simplification – tree rings can sometimes act as a proxy for temperature or for precipitation, depending on the typical climate at a location
(3) https://geni.us/mannhockeystick
(4) https://www.nature.com/articles/s41586-021-03984-4
(5) I’m slightly oversimplifying here, what the paper did was attribute mechanisms to the principal components (PCs) of the temperature timeseries. PCs allow a signal to be broken down into components, ranked by size, that, when combined, reconstruct the signal. Solar and orbital forcing appears to be responsible for PC2, which was itself responsible for 3.5% of the total signal. The vast majority (over 90%) of the warming was accounted for by PC1, which could be explained almost entirely by greenhouse gases and changes in albedo.
(bonus) Ars Technica did a nice article writing this up, if you’d like some more material! https://arstechnica.com/science/2021/11/scientists-extend-and-straighten-iconic-climate-hockey-stick/

Simon Clark