Our very own hockey stick

Everyone with even the slightest interest in climate change has heard of the ‘hockey stick’ which showed in 1998 that recent warming is unprecedented in human history (the background is here, on wikipedia, if you want it).

What we may not have been particularly aware of was that it was based primarily on Northern hemisphere data. In hindsight, that meant there was the ghost of a hope that the temperature trend didn’t apply to Australia, but a team led by Joelle Gergis of Melbourne University has just laid that phantasm to rest: we now have our very own hockey stick.

Temperature reconstruction graph
Fig. 4 from Gergis et al.

The temperature reconstruction uses 27 proxy records, relying equally on tree rings and coral cores, and concludes that summer temperatures in the post-1950 period were warmer than anything else in the last 1000 years at high confidence, and in the last ~400 years at very high confidence.

RealClimate introduces the study here (that’s where I found out about it, in case you hadn’t guessed).

Update, 25 March 2013: A reader recently alerted me to the fact the Gergis et al’s paper was withdrawn before publication. It appears that there were technical flaws in it which meant it didn’t meet the expected standards of proof.

As far as I can determine, however, its conclusions were still probably correct – as one would expect, given that it was only extending northern hemisphere records into the southern hemisphere and one would not expect to find any great north-south difference.

Update 2, June 2020: The original paper seems to have been replaced in 2016 by another by the same authors, Australasian Temperature Reconstructions Spanning the Last Millennium.  Their conclusions are essentially the same:

Regardless, the most recent instrumental temperatures (1985–2014) are above the 90th percentile of all 12 reconstruction ensembles (four reconstruction methods based on three proxy networks—R28, R3, and R2). The reconstructed twentieth-century warming cannot be explained by natural variability alone using GISS-E2-R. In this climate model, anthropogenic forcing is required to produce the rate and magnitude of post-1950 warming observed in the Australasian region.


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