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Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends


From 1979 to 2001, temperatures observed globally by the mid-tropospheric channel of the satellite-borne Microwave Sounding Unit (MSU channel 2), as well as the inferred temperatures in the lower troposphere, show only small warming trends of less than 0.1 K per decade (refs 1–3). Surface temperatures based on in situ observations however, exhibit a larger warming of 0.17 K per decade (refs 4, 5), and global climate models forced by combined anthropogenic and natural factors project an increase in tropospheric temperatures that is somewhat larger than the surface temperature increase6,7,8. Here we show that trends in MSU channel 2 temperatures are weak because the instrument partly records stratospheric temperatures whose large cooling trend9 offsets the contributions of tropospheric warming. We quantify the stratospheric contribution to MSU channel 2 temperatures using MSU channel 4, which records only stratospheric temperatures. The resulting trend of reconstructed tropospheric temperatures from satellite data is physically consistent with the observed surface temperature trend. For the tropics, the tropospheric warming is 1.6 times the surface warming, as expected for a moist adiabatic lapse rate.

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Figure 1: Atmospheric weighting functions and brightness temperature responses.
Figure 2: Time series of monthly mean, global-average temperature anomalies.
Figure 3: Trends in monthly mean temperature anomalies.

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We thank J. M. Wallace for discussions. We also thank J. M. Wallace, D. L. Hartmann, J. R. Holton, J. K. Angell and M. Free for their comments on the manuscript. This study was supported by the US DOE, NSF and NASA.

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Correspondence to Qiang Fu.

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Supplementary information

Supplementary Discussion

Supplementary Table 1: Coefficients in Equation (1); Supplementary Fig.1. Comparison of monthly mean, global-average temperature anomaly time series; Supplementary Table 2: Atmospheric temperature trends shown in Fig.3 with 95% confidence intervals (K/decade). (PDF 64 kb)

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Fu, Q., Johanson, C., Warren, S. et al. Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends. Nature 429, 55–58 (2004).

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