The Influence of Climate Modes on Changes in the Rate of Warming of Global SST.

1. The Influence of Climate Modes on Changes in the Rate of Warming of Global SST. Semyon A. Grodsky, Thomas M. Smith, and James A. Carton *Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742 *NOAA/NESDIS/STAR/SCSD, and CICS/ESSIC, University of Maryland, College Park, College Park, Maryland

2. Annual ERSST.v3b anomaly from 1880-2009 from 60°S and 60°N.

3. Warm anomaly during 1940’s is due to relative increase of US ship measurements (mainly engine room intake, ERI) relative to UK ship measurements (primarily uninsulated bucket). ERI data is biased warm. A large discontinuity in the mid-twentieth century in observed global-mean surface temperature, by Thompson,D.W.J., et al, Nature, 2008

4. Are alternative explanations of the mid-century warming available? Global SST anomaly from the 3 major SST reconstructions

5. Are alternative explanations of the mid-century warming available? Detrended global SST anomaly (degC)

6. Are alternative explanations of the mid-century warming available? Detrended global SST anomaly (degC) after removing the ENSO impacts

7. Are alternative explanations of the mid-century warming available? Detrended global SST anomaly (degC) with the AMO index overlain Atlantic Multidecadal Oscillation Index (AMO)

8. Are alternative explanations of the mid-century warming available? • Caveats • AMO is based on the reconstructed SST that includes possible bias due to ship intake measurements • But, if the bias is due to ship intake, the Pacific (primarily area of US Navy during WWII) should be biased warm while the Atlantic (primarily area of UK Navy) should be biased cold.

9. Spatial patterns and time series of the two leading EOFs of the annually average de-trended non-ENSO anomalous SST

10. Conclusions • Leading EOFs of detrended, non-ENSO anomalous SST don’t resemble noisy patterns typical of instrumental bias. • Warm Pacific/cold Atlantic pattern, expected from the mid 20th century observation shift (switch in relative contribution of US/UK navy observations), is not dominant. • The two decadal SST modes, AMO and PDO, explain about 60% of multidecadal changes in the warming rate of global SST. The leading mode, AMO, explains more than 50%.