Australasian climate—the 1000-year view

To understand the present climate of Earth and reliably predict its future, experts turn to the past. For years, using various proxies, scientists have reconstructed our planet’s climatological history on global, hemispheric, and now regional scales. Such reconstructions—spanning hundreds, thousands, and even millions of years—provide not only context for our current climate but also test beds for models and their uncertainties. Many such reconstructions have led to the conclusion that our current climate is anomalously warm and the anomaly is driven largely by the addition of substantial amounts of greenhouse gases to the atmosphere. The first large historical analysis is now in for Australasia, which encompasses Australia, New Zealand, Indonesia, and the nearby South Pacific area. Led by the University of Melbourne’s Joëlle Gergis, the Past Global Changes Australasia 2K group collated studies of 27 natural climate-proxy records; in the figure, records from tree rings are green; ice cores, orange; and corals, blue. In the resulting rigorously verified 1000-year climate reconstruction, team members saw the warming and cooling trends that appeared in other regional and larger-scale reconstructions, and also effects specific to the region, like the El Niño–southern oscillation. Running a sophisticated climate model, they then found that natural climate variability needed to be supplemented by so-called forcings from solar and volcanic activity to reproduce observed changes in the historical data. However, to account for the unprecedented warming since 1950 the model required additional forcing from greenhouse gases. (J. Gergis et al., J. Clim., in press, doi:10.1175/JCLI-D-11-00649.1 .)—Stephen G. Benka