 |
| Titel |
Evidence for an earlier greenhouse cooling effect in the stratosphere before 1980 over the Northern Hemisphere |
| VerfasserIn |
C. S. Zerefos, K. Tourpali, P. Zanis, K. Eleftheratos, C. Repapis, A. Goodman, D. Wuebbles, I. S. A. Isaksen, J. Luterbacher |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 15 ; Nr. 14, no. 15 (2014-08-01), S.7705-7720 |
| Datensatznummer |
250118917
|
| Publikation (Nr.) |
 copernicus.org/acp-14-7705-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
| This study provides a new look at the observed and calculated long-term
temperature changes from the lower troposphere to the lower stratosphere
since 1958 over the Northern Hemisphere. The data sets include the NCEP/NCAR
reanalysis, the Free University of Berlin (FU-Berlin) and the RICH
radiosonde data sets as well as historical simulations with the CESM1-WACCM
global model participating in CMIP5. The analysis is mainly based on monthly
layer mean temperatures derived from geopotential height thicknesses in
order to take advantage of the use of the independent FU-Berlin
stratospheric data set of geopotential height data since 1957. This approach
was followed to extend the records for the investigation of the
stratospheric temperature trends to the earliest possible time. After
removing the natural variability with an autoregressive multiple regression
model our analysis shows that the period 1958–2011 can be divided into two
distinct sub-periods of long-term temperature variability and trends: before
and after 1980. By calculating trends for the summer time to reduce
interannual variability, the two periods are as follows. From 1958 until
1979, a non-significant trend (0.06 ± 0.06 °C decade−1 for NCEP) and
slightly cooling trends (−0.12 ± 0.06 °C decade−1 for RICH) are
found in the lower troposphere. The second period from 1980 to the end of
the records shows significant warming (0.25 ± 0.05 °C decade−1 for
both NCEP and RICH). Above the tropopause a significant cooling trend is
clearly 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−1
for RICH and −0.48 ± 0.20 °C decade−1 for FU-Berlin) and the
post-1980 period (−0.79 ± 0.18 °C decade−1 for NCEP, −0.66 ± 0.16 °C decade−1
for RICH and −0.82 ± 0.19 °C decade−1 for
FU-Berlin). The cooling in the lower stratosphere persists throughout
the year from the tropics up to 60° N. At polar
latitudes competing dynamical and radiative processes reduce the
statistical significance of these trends. Model results are in line with
reanalysis 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 lower
stratosphere CESM1-WACCM modelled trends are generally lower than
reanalysis and the observations. The contrasting effects of ozone depletion
at polar latitudes in winter/spring and the anticipated strengthening of the
Brewer–Dobson circulation from man-made global warming at polar latitudes
are discussed. Our results provide additional evidence for an early
greenhouse cooling signal in the lower stratosphere before 1980, which
appears well in advance relative to the tropospheric greenhouse warming
signal. The suitability of early warning signals in the stratosphere
relative to the troposphere is supported by the fact that the stratosphere
is less sensitive to changes due to cloudiness, humidity and man-made
aerosols. Our analysis also indicates that the relative contribution of the
lower stratosphere versus the upper troposphere low-frequency variability is
important for understanding the added value of the long-term tropopause
variability related to human-induced global warming. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|