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This study provides a new look at the observed and calculated long-termtemperature changes from the lower troposphere to the lower stratospheresince 1958 over the Northern Hemisphere. The data sets include the NCEP/NCARreanalysis, the Free University of Berlin (FU-Berlin) and the RICHradiosonde data sets as well as historical simulations with the CESM1-WACCMglobal model participating in CMIP5. The analysis is mainly based on monthlylayer mean temperatures derived from geopotential height thicknesses inorder to take advantage of the use of the independent FU-Berlinstratospheric data set of geopotential height data since 1957. This approachwas followed to extend the records for the investigation of thestratospheric temperature trends to the earliest possible time. Afterremoving the natural variability with an autoregressive multiple regressionmodel our analysis shows that the period 1958–2011 can be divided into twodistinct sub-periods of long-term temperature variability and trends: beforeand after 1980. By calculating trends for the summer time to reduceinterannual variability, the two periods are as follows. From 1958 until1979, a non-significant trend (0.06 ± 0.06 °C decade−1 for NCEP) andslightly cooling trends (−0.12 ± 0.06 °C decade−1 for RICH) arefound in the lower troposphere. The second period from 1980 to the end ofthe records shows significant warming (0.25 ± 0.05 °C decade−1 forboth NCEP and RICH). Above the tropopause a significant cooling trend isclearly seen in the lower stratosphere both in the pre-1980 period(−0.58 ± 0.17 °C decade−1 for NCEP, −0.30 ± 0.16 °C decade−1for RICH and −0.48 ± 0.20 °C decade−1 for FU-Berlin) and thepost-1980 period (−0.79 ± 0.18 °C decade−1 for NCEP, −0.66 ± 0.16 °C decade−1for RICH and −0.82 ± 0.19 °C decade−1 forFU-Berlin). The cooling in the lower stratosphere persists throughoutthe year from the tropics up to 60° N. At polarlatitudes competing dynamical and radiative processes reduce thestatistical significance of these trends. Model results are in line withreanalysis and the observations, indicating a persistent cooling (−0.33 °C decade−1)in the lower stratosphere during summer before and after 1980; a feature that is also seen throughout the year. However, the lowerstratosphere CESM1-WACCM modelled trends are generally lower thanreanalysis and the observations. The contrasting effects of ozone depletionat polar latitudes in winter/spring and the anticipated strengthening of theBrewer–Dobson circulation from man-made global warming at polar latitudesare discussed. Our results provide additional evidence for an earlygreenhouse cooling signal in the lower stratosphere before 1980, which appears well in advance relative to the tropospheric greenhouse warmingsignal. The suitability of early warning signals in the stratosphererelative to the troposphere is supported by the fact that the stratosphereis less sensitive to changes due to cloudiness, humidity and man-madeaerosols. Our analysis also indicates that the relative contribution of thelower stratosphere versus the upper troposphere low-frequency variability isimportant for understanding the added value of the long-term tropopausevariability related to human-induced global warming

Evidence for an earlier greenhouse cooling effect in the stratosphere before 1980 over the Northern Hemisphere