We thank Hank Seidel for support with graphics. Ben Santer helped in numerous aspects of the work and provided very thorough and useful comments as a reviewer. We also thank him for sharing preprocessed model data with us. We would also like to thank the following people: two further anonymous reviewers, John Christy, Nathan Gillett, Simon Brown, Myles Allen, David Thompson, and Jim Hurrell for discussions; and Phil Jones, John Christy, and David Parker for observational data. Todd Mitchell provided indices for variability and was very helpful in many aspects of the work. GCH was supported by a fellowship from the Alexander von Humboldt foundation, by NSF Grants ATM-9707069, ATM-0096017, and ATM-0296007, by JISAO, NOAAs Office of Global programs, and DOE in conjunction with the Climate Change Data and Detection element and by Duke University. Any opinions, findings, and conclusions expressed in this paper are those of the authors and do not necessarily reflect the views of the funding agencies.
Allen, M. R., and P. A. Stott, 2002: Estimating signal amplitudes in optimal fingerprinting: Part I. Theory. Climate Dyn., in press.
Bengtsson, L., E. Roeckner, and M. Stendel, 1999: Why is the global warming proceeding much slower than expected. J. Geophys. Res., 104 , 3865–3876.
Brown, S. J., D. E. Parker, C. K. Folland, and I. Macadam, 2000a: Decadal variability in the lower-tropospheric lapse rate. Geophys. Res. Lett., 27 , 997–1000.
Brown, S. J., and D. Sexton, 2000b: Differential changes in observed surface and atmospheric temperature since 1979. Hadley Centre Tech. Note HCTN12, 41 pp.
Chang, P., R. Saravanan, L. Ji, and G. C. Hegerl, 2000: The effect of local sea surface temperature on atmospheric circulation over the tropical Atlantic sector. J. Climate, 13 , 2195–2216.
Chelliah, M., and C. F. Ropelewski, 2000: Reanalysis based tropospheric temperature estimates: Uncertainties in the context of global climate change detection. J. Climate, 13 , 3187–3205.
Christy, J. R., R. W. Spencer, and W. D. Braswell, 2000: MSU tropospheric temperatures: Dataset construction and radiosonde comparisons. J. Atmos. Oceanic Technol., 17 , 1153–1170.
Gaffen, D. J., B. D. Santer, J. S. Boyle, J. R. Christy, N. E. Graham, and R. J. Ross, 2000: Multidecadal changes in vertical temperature structure of the tropical troposphere. Science, 287 , 1242–1245.
Gillett, N., M. R. Allen, and S. F. B. Tett, 2000: Modeled and observed variability in atmospheric vertical temperature structure. Climate Dyn., 16 , 49–61.
Hill, D. C., M. R. Allen, and P. A. Stott, 2001: Allowing for solar forcing in the detection of human influence on tropospheric temperatures. Geophys. Res. Lett., 28 , 1555–1558.
Houghton, J. T., L. G. Meiro Filho, B. A. Callander, N. Harris, A. Kattenberg, and K. Maskell, Eds. 1996: Climate Change 1995: The Science of Climate Change. Cambridge University Press, 572 pp.
Houghton, J. T., Y. Ding, D. J. Griggs, M. Noguer, P. J. van der Linden, X. Dai, K. Maskell, and C. A. Johnson, Eds.,. 2001: Climate Change 2000: The Scientific Basis. Cambridge University Press, 892 pp.
Hurrell, J. W., and K. E. Trenberth, 1998: Difficulties in obtaining reliable temperature trends: Reconciling the surface and satellite MSU records. J. Climate, 11 , 945–967.
Jones, P. D., 1994: Hemispheric surface air temperature variations: A reanalysis and an update to 1993. J. Climate, 7 , 1794–1802.
Jones, P. D., M. New, D. E. Parker, S. Martin, and I. G. Rigor, 1999: Surface air temperature and its changes over the past 150 years. Rev. Geophys., 37 , 173–199.
Lean, J., J. Beer, and R. Bradley, 1995: Reconstruction of solar irradiance since 1600: Implications for climate change. Geophys. Res. Lett., 22 , 3195–3198.
Mantua, J. N., R. S. Hare, Y. Zhang, J. M. Wallace, and R. C. Francis, 1997: A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. Amer. Meteor. Soc., 78 , 1069–1080.
Parker, D. E., C. K. Folland, and M. Jackson, 1995: Marine surface temperature: Observed variations and data requirements. Climate Change, 31 , 559–600.
Parker, D. E., M. Gordon, D. P. N. Cullum, D. M. H. Sexton, C. K. Folland, and N. Rayner, 1997: A new global gridded radiosonde temperature data base and recent temperature trends. Geophys. Res. Lett., 24 , 1499–1502.
Roeckner, E., L. Bengtsson, J. Feichter, J. Lelieveld, and H. Rodhe, 1999: Transient climate change simulations with a coupled atmosphere–ocean GCM including the tropospheric sulfur cycle. J. Climate, 12 , 3004–3032.
Santer, B. D., J. J. Hnilo, T. M. L. Wigley, J. S. Boyle, C. Doutriaux, M. Fiorino, D. E. Parker, and K. E. Taylor, 1999: Uncertainties in “observational” estimates of temperature change in the free atmosphere. J. Geophys. Res., 104 , 6305–6333.
Santer, B. D., and Coauthors. 2000a: Interpreting differential temperature trends at the surface and in the lower troposphere. Science, 287 , 1227–1231.
Santer, B. D., and Coauthors. 2000b: Statistical significance of trends and trend differences in layer average atmospheric temperature time series. J. Geophys. Res., 105 , 7337–7356.
Santer, B. D., and Coauthors. 2001: Accounting for the effects of volcanoes and ENSO in comparisons of modeled and observed temperature trends. J. Geophys. Res., 106 , 28033–28059.
Spencer, R. W., and J. R. Christy, 1992: Precision and radiosonde validation of satellite gridpoint temperature anomalies. Part II: A tropospheric retrieval and trends during 1979–90. J. Climate, 5 , 858–866.
Stott, P. A., S. F. B. Tett, G. S. Jones, M. R. Allen, J. F. B. Mitchell, and G. J. Jenkins, 2000: External control of 20th century temperature by natural and anthropogenic forcings. Science, 290 , 2133–2137.
Tett, S. F. B., J. F. B. Mitchell, D. E. Parker, and M. R. Allen, 1996: Human influence on the atmospheric vertical temperature structure: Detection and observations. Science, 274 , 1170–1173.
Thompson, D. W. J., and J. M. Wallace, 1998: The Arctic Oscillation signature in wintertime geopotential height and temperature fields. Geophys. Res. Lett., 25 , 1297–1300.
Thompson, D. W. J., and G. C. Hegerl, 2000: Annular modes in the extratropical circulation. Part II: Trends. J. Climate, 13 , 1018–1036.
Venzke, S., M. R. Allen, R. T. Sutton, and D. P. Rowell, 1999: The atmospheric response over the North Atlantic to decadal changes in sea surface temperature. J. Climate, 12 , 2562–2584.
Wallace, J. M., Y. Zhang, and J. A. Renwick, 1995: Dynamic contribution to hemispheric mean temperature trends. Science, 270 , 780–783.
Wentz, F. J., and M. Schabel, 1998: Effects of orbital decay on satellite-derived lower-tropospheric trends. Nature, 344 , 661–664.
Wentz, F. J., C. Mears, and D. Seidel, 2001: Lower tropospheric air temperature derived from a blended analysis of MSU, SSM/T1, SSM/I, NCEP/NCAR reanalysis, and Reynolds SST. RSS Tech. Rep. 062801, Remote Sensing Systems, Santa Rosa, CA, 46 pp.
Yulaeva, E., and J. M. Wallace, 1994: The signature of ENSO in global temperature and precipitation fields derived from the microwave sounding unit. J. Climate, 7 , 1719–1736.