Federal Departement of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Revisiting Swiss temperature trends * Paulo Ceppi, Simon C. Scherrer, Andreas M. Fischer, Christof Appenzeller Federal of Office of Meteorology and Climatology MeteoSwiss 16 July th International Meeting on Statistical Climatology, Edinburgh UK * submitted to the International Journal of Climatology
2 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Motivation Temperature trends: The hallmark of climate change IPCC 2007, WG1 seasonal differences different processes on different spatial scales local climate change = large scale + local processes new Swiss grid
3 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Outline Geographical setting, input data and gridding What are the linear temperature trends (yearly / seasonal)? Can regional climate models explain the observed trends? What is the trend contribution of … large scale circulation? … local factors? Conclusions
4 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Geographical setting and input data 91 homogeneous station series, station altitude range: 203 to 3580 m asl ~2 km x 2 km gridded data set Edinburgh Switzerland
5 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Monthly anomaly gridding climatological distance λ spatial interpolation of altitude corrected residuals influence of topography determined independently every month C. Frei, MeteoSwiss valley setting λ = 0.01 λ = 0.05λ = 0.1 summit setting
6 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Gridded temperature anomalies Example December 2009 good representation of local/altitude effects! C. Frei, MeteoSwiss topography
7 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Yearly temperature trends (°C/10yrs) average OLS trend: +0.35°C/10yrs stronger trends than in global mean (+0.13°C/10yrs) highly significant trends everywhere (p < ) small spatial variability no altitude dependence
8 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Seasonal temperature trends (°C/10yrs) °C/10yrs trends positive, (almost) everywhere significant large seasonal differences of the trends [°C/10yrs] autumn weak ( ), summer strong ( ) clearly larger than NH-land (exception autumn) altitude depences in autumn (stronger for low altitudes) NH-land trend [°C/10yrs] density SON JJA MAM DJF
9 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Can climate models reproduce warming? Northern Switzerland ENSEMBLES models (smoothed) observed change (smoothed) anomaly [°C] wrt yr Gaussian smoothing but: models are NOT forced with observed circulation! Can observed circulation changes explain the differences?
10 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Different warming by circulation changes? Linear regression model Quantify effect of circulation on T via regression model: principal components (PCs) of geopotential height at 500 hPa over N-Atlantic/Europe model calibration: / validation: choice of PCs by „stepwise selection“ observed temperatures “modell error” other effects atmospheric circulation
11 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Circulation effects on temperature Swiss mean trend lines observed / modelled trend (°C/10yrs) observed / modelled temperatures bright: calibrationdark: validation
12 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Summary temperature trend analysis Switzerland [°C/10yrs] DJFMAMJJASONYEAR observed circulation 0.21 (54%) 0.08 (21%) 0.07 (15%) 0.02 (12%) 0.13 (37%) residual Can regional climate models account for the residual (circulation corrected) trends?
13 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Summary temperature trend analysis Switzerland [°C/10yrs] DJFMAMJJASONYEAR observed circulation 0.21 (54%) 0.08 (21%) 0.07 (15%) 0.02 (12%) 0.13 (37%) residual RCM
14 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh trend (°C/10yrs) Altitude dependence gridded temperature trends negative anomaly °C/10yrs altitude [m asl] positive anomaly
15 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Swiss temperature trend anomalies [°C/10yrs] month-to-month evolution altitude [m asl] month of the year more trend than all altitude average less trend than all altitude average DecJanFebMarAprMayJunJulAugSepOctNovDec changes in fog/visibility?
16 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Swiss temperature trend anomalies [°C/10yrs] incl. mean temperature evolution [°C] altitude [m asl] month of the year more trend than all altitude average less trend than all altitude average DecJanFebMarAprMayJunJulAugSepOctNovDec
17 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh altitude [m asl] month of the year Swiss temperature trend anomalies [°C/10yrs] … and mean snow pack [cm] more trend than all altitude average less trend than all altitude average snow-albedo effect? DecJanFebMarAprMayJunJulAugSepOctNovDec
18 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Conclusions Swiss temperature trends stronger than NH-land trend ( 1.6) Large seasonal differences, altitude dependence in autumn ~50% of the trend in winter due to changes in circulation – much less in other seasons Regional climate models underestimate circulation corrected trends in spring & summer Local processes important for local trends, especially in autumn (fog), spring (snow-albedo effect) and summer
19 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh 21 RCM-GCM-chains from the ENSEMBLES project mean of 21 ENSEMBLES runs Altitude dependences observed, circulation-corrected, regional climate models (RCMs) trend (°C/10yrs) observed trends circulation corrected (residual) trend altitude [m asl]
20 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Circulation corrected series Signal of global forcing & local effects (e.g. visibility, snow-albedo, soil-atm.) Can climate models account for these circulation corrected trends?
21 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Observed time series Swiss mean Can changes in circulation explain these differences?
22 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Northern Switzerland temperature changes Observation and models (ENSEMBLES RCM) IA range ENSEMBLES models smoothed ENSEMBLES models IA observed changes 20yr smoothed observed change anomaly [°C] wrt
23 Revisiting Swiss temperature trends | 11th IMSC, 16 July 2010, Edinburgh Altitude dependences of circulation effect observed vs. circulation contribution trend (°C/10yrs) altitude [m asl] observed trend circulation trend