Journal article

Observed Emergence of the Climate Change Signal: From the Familiar to the Unknown

E Hawkins, D Frame, L Harrington, M Joshi, A King, M Rojas, R Sutton



Changes in climate are usually considered in terms of trends or differences over time. However, for many impacts requiring adaptation, it is the amplitude of the change relative to the local amplitude of climate variability which is more relevant. Here, we develop the concept of “signal-to-noise” in observations of local temperature, highlighting that many regions are already experiencing a climate which would be “unknown” by late 19th century standards. The emergence of observed temperature changes over both land and ocean is clearest in tropical regions, in contrast to the regions of largest change which are in the northern extratropics—broadly consistent with climate model simulations. Si..

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University of Melbourne Researchers


Awarded by European Union

Awarded by Australian Research Council

Awarded by UK Natural Environment Research Council


Awarded by Whakahura project - Endeavour Fund

Funding Acknowledgements

We thank Nicola Maher for providing the MPI large ensemble data. We also thank the anonymous reviewer, Flavio Lehner, and Richard Betts for useful comments which helped improve the paper. E. H. and R. S. were supported by the National Centre for Atmospheric Science, and E. H. was funded by the ERA4CS INDECIS project with funding from the European Union Grant 690462. A. D. K. was funded by the Australian Research Council (DE180100638). M. J. is funded by UK Natural Environment Research Council Grants NE/S004645/1 and NE/N018486/1. M. R. acknowledges funding from FONDAP-CONICYT 15110009. D. J. F. and L. J. H. were supported by the Whakahura project funded by the Endeavour Fund (Contract RTVU1906). The data sets used in this paper are freely available online: Berkeley Earth (, Cowtan & Way (, HadCRUT4 (, GISTEMP (, NOAA GlobTemp (, GPCC (, HadUK-Grid (, andMPI Large Ensemble ( Oxford Radcliffe Observatory temperature data is available online ( annual_mean_temperatures_1814_to_ date_xlsx/10322015).