1. Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado 80523, USA
2. Met Office Hadley Centre, Exeter EX1 3PB, UK
3. Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195, USA
4. Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK

Correspondence to: David W. J. Thompson¹ Correspondence and requests for materials should be addressed to D.W.J.T. (Email: davet@atmos.colostate.edu).

Abstract

Data sets used to monitor the Earth's climate indicate that the surface of the Earth warmed from 1910 to 1940, cooled slightly from 1940 to 1970, and then warmed markedly from 1970 onward¹. The weak cooling apparent in the middle part of the century has been interpreted in the context of a variety of physical factors, such as atmosphere–ocean interactions and anthropogenic emissions of sulphate aerosols². Here we call attention to a previously overlooked discontinuity in the record at 1945, which is a prominent feature of the cooling trend in the mid-twentieth century. The discontinuity is evident in published versions of the global-mean temperature time series¹, but stands out more clearly after the data are filtered for the effects of internal climate variability. We argue that the abrupt temperature drop of 0.3 °C in 1945 is the apparent result of uncorrected instrumental biases in the sea surface temperature record. Corrections for the discontinuity are expected to alter the character of mid-twentieth century temperature variability but not estimates of the century-long trend in global-mean temperatures.

1. Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado 80523, USA
2. Met Office Hadley Centre, Exeter EX1 3PB, UK
3. Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195, USA
4. Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK

Correspondence to: David W. J. Thompson¹ Correspondence and requests for materials should be addressed to D.W.J.T. (Email: davet@atmos.colostate.edu).

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