Thursday, May 17, 2012

Australasian warming since 1950 unmatched over last 1000 years

As widely reported in the media, Australian scientists have for the first time created a detailed 1000 year reconstruction of temperatures in Australasia. Although there were no man made thermometers over most of this time, nature contains a number of natural thermometers (like tree rings, corals and ice cores) that scientists can read to piece together many details of temperature and climate in the past. By combining records from a number of different sites scientists have created a temperature record stretching back to AD 1000.

Three main conclusions can be drawn from this paper:

  1. The warmth of the climate in Australasia post-1950 is not equaled or surpassed by any time period in the last 1000 years.
  2. The hottest 30 year period was 1970-2000.  (Nb1: the record did not carry on past 2000, Nb2: 30 years is a standard length of time used to look at "climate" as opposed to short term temperature fluctuations)
  3. "The unusual 20th century warming cannot be explained by natural variability alone, suggesting a strong influence of anthropogenic forcing (human caused warming) in the Australasian region"

The figure below show's their temperature reconstruction (click on it to embiggen):

Figure 4: Reconstruction of australasian temperatures since 1000 AD compared to 1961-1990 average from thermometers. Black line is 30 year average temperature. Green line is thermometer temperature record for Australasia. Thick black line shows periods with most reliable measurements, thin black line shows when temperature measurements are not so reliable. Shading above and below average line shows the uncertainty of the measurement (this represents the fact that the true average temperature may not be exactly what was reconstructed and shown in the black line, however there will be a very high likelihood the true temperature was within the shaded region).
Both the temperature increase and temperatures in recent times are not matched elsewhere on the graph. Note that although the top of the shaded uncertainty plots do rise above the 1961-1900 average temperature on several occasions the evidence does not support them being warmer. Whereas in recent times the average reconstructed temperature including uncertainty has risen above the 1961-1900 average temperature.
From Gergis et al, 2012. Copyright 2012 American Meteorological Society

Abstract of scientific article can be read here, unfortunately the full paper is behind the journals paywall.

Gergis, J., R. Neukom, S. Phipps, A. Gallant, and D. Karoly, 2012: Evidence of unusual late 20th century warming from an Australasian temperature reconstruction spanning the last millennium. J. Climate. doi:10.1175/JCLI-D-11-00649.1, in press.

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