Tracking regional temperature projections from the early 1990s in light of variations in regional warming, including ‘warming holes’
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The perception of the accuracy of regional climate projections made in the early 1990s about climate change by 2030 may be influenced by how the temperature trend has changed in the 25 years since their publication. However, temperature trends over this period were influenced not only by external forcings such as greenhouse gases but also natural variations. The temperature of Southern Australia, the Sahel, South Asia and Southern Europe are currently within the warming estimates from statements in the early 1990s from the IPCC and CSIRO, assuming a linear trend between 1990 and 2030. However, northern Australia and central North America are currently at the lower limit or below these projections, having featured areas of multi-year regional cooling during global warming, sometimes called ‘warming holes’. Recent climate model simulations suggest that cooling can be expected in the recent past and near future in some regions, including in Australia and the US, and that cooling is less likely over 1990–2030 than in 1990–2015, bringing observations closer to the IPCC and CSIRO warming estimates by 2030. Cooling at the 25-year scale in some regions can be associated with cyclic variability such as the Inter-decadal Pacific Oscillation, or low trend such as in the Southern Ocean. Explicitly communicating the variability in regional warming rates in climate projections, including the possibility of regional warming ‘holes’ (or the opposite of ‘surges’ or ‘peaks’) would help to set more reliable expectations by users of those projections.
KeywordsRegional climate change Climate variability Climate projections
This work was supported by the National Environmental Science Program (NESP) Earth System and Climate Change hub. We thank Didier Monselesan and Kevin Hennessy for discussions during the development of the paper. We thank and acknowledge Kevin Cowtan and Robert Way at the University of York and the Australian Bureau of Meteorology for provision of observed datasets.
We thank the PCMDI and the World Climate Research Program’s Working Group on Coupled Modelling for their roles in making available the CMIP3 and CMIP5 multi-model datasets. Support of this dataset is provided by the Office of Science, US Department of Energy. More details on model documentation are available at the PCMDI website (www.pcmdi.llnl.gov).
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