Abstract
Very few annually resolved millennial-length temperature reconstructions exist for the Southern Hemisphere. Here we present four 979-year reconstructions for southeastern Australia for the austral summer months of December–February. Two of the reconstructions are based on the Australian Water Availability Project dataset and two on the Berkeley Earth Surface Temperature dataset. For each climate data set, one reconstruction is based solely on Lagarostrobos franklinii (restricted reconstructions) while the other is based on multiple Tasmanian conifer species (unrestricted reconstructions). Each reconstruction calibrates ~50−60% of the variance in the temperature datasets depending on the number of tree-ring records available for the reconstruction. We found little difference in the temporal variability of the reconstructions, although extremes are amplified in the restricted reconstructions relative to the unrestricted reconstructions. The reconstructions highlight the occurrence of numerous individual years, especially in the 15th−17th Centuries, for which temperatures were comparable with those of the late 20th Century. The 1950−1999 period, however, stands out as the warmest 50-year period on average for the past 979 years, with a sustained shift away from relatively low mean temperatures, the length of which is unique in the 979-year record. The reconstructions are strongly and positively related to temperatures across the southeast of the Australian continent, negatively related to temperatures in the north and northeast of the continent, and uncorrelated with temperatures in the west. The lack of a strong relationship with temperatures across the continent highlights the necessity of a sub-regional focus for Australasian temperature reconstructions.
Highlights
Since 1910 Australian temperatures have increased on average by ∼0.9 ◦C, and much of this increase has been sustained since 1970
We present four 979-year mean temperature reconstructions for the austral summer months (December–February) for southeastern Australia, a region impacted by multiple ocean-atmosphere processes including the El Niño-Southern Oscillation, the Southern Annular Mode and the Indian Ocean Dipole
The seasonal targets differ for our new reconstructions and the Cook et al (2000) November–April reconstruction, both reconstructions are for Tasmania only, so comparison with our reconstructions seems reasonable
Summary
Since 1910 Australian temperatures have increased on average by ∼0.9 ◦C, and much of this increase has been sustained since 1970 (www.bom.gov.au). Over the past two decades, significant efforts have extended the annually resolved Australasian temperature record by several hundred years (Cook et al 2000, 2002, PAGES 2 K Consortium 2013, Saunders et al 2013, O’Donnell et al 2016, Gergis et al 2016). Without exception, these reconstructions show a strong and sustained temperature increase since at least the mid20th Century (Cook et al 2000 (November−April mean temperature); Gergis et al 2016 (September−February mean temperature); O’Donnell et al 2016 (January maximum temperature); Saunders et al (2013, annual mean temperature)). Two of the longest reconstructions (Cook et al 2000, Gergis et al 2016) suggest recent temperatures are highly unusual in the context of the past millennium
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