Eurasian winter cooling in the warming hiatus of 1998-2012 Chao Li, Bjorn Stevens, Jochem Marotzke Max-Planck-Institut für Meteorologie Hamburg 7 July 2015, OCFCC in Paris, France (Email: [email protected])
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Eurasian winter cooling in the warming
hiatus of 1998-2012
Chao Li, Bjorn Stevens, Jochem Marotzke
Max-Planck-Institut für Meteorologie
Hamburg
7 July 2015, OCFCC in Paris, France
(Email: [email protected])
Introduction
Tropical Pacific cooling (e.g. Meehl et al., 2011; Kosaka and Xie, 2013)
Anomalously cold NH winter land surface (Cohen et al., 2012)
Incomplete observational coverage over Arctic (Cowtan and Way, 2013)
A possible artifact of data biases over the Ocean (Karl et al., 2015)
The present study:
• Investigate the relative magnitudes of the contributions of surface
temperature trends from different latitude bands to recent warming hiatus;
• Explore the cause of NH mid-latitude winter cooling with large ensembles
of sensitivity simulations with an atmospheric model.
Where does the warming hiatus of 1998-2012 come from?
Scaled zonal-mean surface temperature trends
• A pronounced NH winter cooling within 30°N~60°N;
• The warming hiatus is strongly influenced by a NH mid-latitude winter cooling.
What is the driver of the Eurasian winter cooling of 1998-2012?
Model and experimental design
Model:
ECHAM6: horizontal resolution T63 (1.9º), 47 vertical levels up to 0.01 hPa;
JSBACH: a subsystem for land and vegetation in ECHAM6
AMIP (20 realization)
90°N
90°S
ACLI (20 realization)
GCLI (20 realization)
Observed SST and sea ice in 1979-2012 Observed SST and
sea ice in 1979-2012
Climatology annual cycle of SST
Climatology annual cycle of SST
Standard CMIP5 AMIP
simulations
No SST variation in
Arctic
No SST variation
0°
Eurasia winter cooling versus DJF blocking frequency trend
AMIP: With SST/SIC variations
ACLI: no Arctic SST/SIC variations
GCLI: no SST/SIC variations
1998-2012
Ts trend blocking
AMIP/ACLI 1.52** 1.47**
AMIP/GCLI 1.34** 1.6**
ACLI/GCLI 0.88 1.08
Variances ratio
(** significant with bootstrapping test)
Conclusion
The GMST trend in 1998-2012 is strongly influenced by a pronounced
Eurasian winter cooling trend.
The observed Eurasian winter cooling trend over 1998-2012 arises
essentially from atmospheric internal variability and constitutes an extreme
climate event.
The Arctic sea-ice loss and SST changes do not drive systematic changes
in the NH large-scale circulation nor the Eurasian winter blocking frequency
in 1998-2012.
The dramatic change in Arctic sea ice and SSTs enhances the variability of
Eurasian winter climate and thus increases the probability of an extreme
Eurasian winter cooling trend.
Conclusion
Thanks for your attention!
The GMST trend in 1998-2012 is strongly influenced by a pronounced
Eurasian winter cooling trend.
The observed Eurasian winter cooling trend over 1998-2012 arises
essentially from atmospheric internal variability and constitutes an extreme
climate event.
The Arctic sea-ice loss and SST changes do not drive systematic changes
in the NH large-scale circulation nor the Eurasian winter blocking frequency
in 1998-2012.
The dramatic change in Arctic sea ice and SSTs enhances the variability of
Eurasian winter climate and thus increases the probability of an extreme
Eurasian winter cooling trend.
Monthly GMST trend
Warming trend in all
seasons.
Cooling trend in NH Winter
(DJF), which compensates
warming in other seasons.
Large-scale atmospheric circulation change
Arctic sea-ice change does not
drive systematical changes of NH
large-scale atmospheric circulation
in the past decades.
ECHAM6 can reasonably simulate
the variations of NH large-scale
atmospheric circulation changes.
NH mid-latitude DJF temperature trend
and NH blocking frequency
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