The 1000 year Australian hockey itch

See Cook et al., 2000…

With the collection and dating of additional sub-fossil Huon pine wood from Mt. Read, Cook et al. (1996a) extended the Tasmanian temperature reconstruction back to 800 BC. New spectral analyses of this 2792-year reconstruction again verified the probable existence of the previously identified inter-decadal and century-scale oscillatory modes, now with mean periods of 31, 56, 78, and 200 years. Using singular spectrum analysis (Vautard et al. 1992), Cook et al. (1996a) showed that these oscillatory modes were present throughout the record, but were strongly amplitude modulated. Collectively, they explained about 12% of the variance in the unfiltered temperature reconstruction and about 41% of variance in the 10-year low-pass filtered reconstruction. Interestingly, these modes could also account for approximately 51% of the warming over Tasmania since 1965, with the remaining 49% due to other processes. Finally, Cook et al. (1996a) showed how these natural oscillatory modes could theoretically mask future warming trends over Tasmania due to greenhouse gas forcing.

“New spectral analyses of this 2792-year reconstruction again verified the probable existence of the previously identified inter-decadal and century-scale oscillatory modes, now with mean periods of 31, 56, 78, and 200 years.”
Reconstructions are built from real data (AKA observations). The *real data* “again verified the probable existence of the previously identified inter-decadal and century-scale oscillatory modes, now with mean periods of 31, 56, 78, and 200 years.”
A 200-yr “century-scale” oscillation would look a lot like a “long-term trend” to people unfamiliar with spectral analyses. Like this:
Tasmania 1800-2011
I used a tree ring reconstruction from Mt. Read and the instrumental record from Hobart Airport…
Tasmania Map
To build a quick warm season climate reconstruction for Tasmania over the last ~3,600 years…
Tasmania 3600-yr
The last 60 years may very well have been the warmest 60-yr period over the last millennium. It might be 0.1°C than the 60-yr peak in the early 1400’s. So what?
Prior to the Little Ice Age, these sorts of peaks were hit roughly once every 200 years. The peaks were anywhere from 15.2-15.5°C. The average temperature at Hobart Airport over its 54-yr record is 15.5°C.
The Little Ice Age was possibly the coldest part of the Holocene since the 8.2 KYA Cooling Event. The LIA was cold because the millennial-scale cycle was in its cold phase, there were several deep solar minima and there was an anomalous period of volcanic activity ca 1200-1400 AD, most notably the ca 1300 AD eruption of El Chichón. The peaks of the ~200-yr cycle were suppressed by from ~1400 AD through the end of the LIA.
From the Guardian article…

Dr. Steven Phipps, from the Climate Change Research Centre at the University of New South Wales, who carried out the modeling, said the study demonstrated strong human influence on the climate in the region.
“The models showed that prior to 1850 there were not any long-term trends and temperature variations were likely to be caused by natural climate variability which is a random process,” he said.
“But [the modeling showed] 20th-century warming significantly exceeds the amplitude of natural climate variability and demonstrates that the recent warming experience in Australia is unprecedented within the context of the last millennium.”

Modeling will show whatever the modeler wants it to show.
The paper is pretty interesting. Here’s their proxy reconstruction ensemble:
Gergis Ensemble
One of the things that immediately caught my eye was the fact that the onset of the anomalous warming in their multi-proxy reconstruction coincided with the anomalously cold period in the early 1900’sand that when I plot their reconstruction on my much longer reconstruction, the last 60 years do not appear anomalous at all.
Gergis in Late Holocene Context
Gergis et al. have once again rediscovered the warm-up from the Little Ice Age.