1. Radiative Forcing - Measured at Earth‘s Surface - Explains how Temperature Increases in Europe Rolf Philipona, Bruno Dürr, Christoph Marty, Atsumu Ohmura* and Martin Wild* Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center, Davos Dorf, Switzerland * Institut for Atmospheric and Climate Science, Swiss Federal Institute of Technology (ETH), Zürich, Switzerland

2. Outline Rapid temperature increase in central Europe in the context of - Shortwave radiative forcing - Longwave radiative forcings - Full radiation budget - Cloud radiative forcing Water vapor and the increasing greenhouse effect

3. Alpine Surface Radiation Budget Measurements -5° -10° 50° 45° Central Europe Temperature records by Phil Jones et al.

4. Temperature increase in Central Europe versus Northern Hemisphere [P. Jones http://www.cru.uea.ac.uk/cru/climon/data/] Tave (1978-1987) minus Tave (1900-1909) Tave (1994-2003) minus Tave (1978-1987) 1900 - 2003

5. Temperature CE and NH versus Alps 1900 - 2003 1980 - 20021980 - 2003

6. ASRB - Network Alpine Surface Radiation Budget in Switzerland ANETZ Stations

7. Parallel shortwave downward radiation measurements at 6 collocated ANETZ / ASRB stations By MeteoSwiss with CM5 at ANETZ since 1981 By PMOD/WRC with CM21 at ASRB since 1995 Stations: Locarno-Monti, Payerne, Davos, Cimetta, Weissfluhjoch and Jungfraujoch

8. ASRB-Station Gornergrat

9. ASRB - Station VSF Weissfluhjoch

10. Increase of Temperature and Humidity in the Alps 1980-2002 Temperature [ °C ] Year Absolute Humidity [ g m -3 ] Year

11. Decreasing shortwave downward radiation SDR 1995 - 2003 1981 - 2003 Rather decreasing SDR trend since 1981, except if Summer 2003 is included 1995 - 20021981 - 2002

12. The Earth‘s annual and global mean energy budget Solar (shortwave) Radiation Thermal infrared (longwave) Radiation 31% 49% 20% [ Kiehl and Trenberth, 1997 ] LOR LUR LDR = LDR cfr +LCE SNR SUR TNR = THR – LUR SNR = SDR - SUR THR = SNR + LDR SDR Radiation budget at Earth’s surface

13. 1995 - 2003 Longwave Cloud Effect Shortwave Downward Rad. Longwave Downward Rad. Total Heating Rad. Longwave Upward Rad. (or Temperature) Total Net Radiation 1995 - 2002 Radiation Budget

14. Very high correlation between cloud-free LDR cfr and Temperature and Humidity Cloud-free Longwave Downward Rad. Longwave Upward Rad. (or Temperature) 1995 - 2002 1995 - 2003 LDR cf highly correlated with temperature Cloud-free Longwave Downward Rad. (no Temp. incr.) LDR cf,ts well correlated with absolute humidity [Philipona et al., GRL, 31, 2004][Philipona and Dürr, GRL, accepted]

15. Conclusions Shortwave downward radiation at the surface rather decreases Clouds are increasing during the winter half year producing a longwave warming and decrease during summer half year producing a shortwave warming The surface temperatur rise in central Europe is driven by strongly increasing cloud-free longwave downward radiation caused by a rapid increase of the greenhouse effect over land [Philipona et al., GRL, 31, 2004][Philipona and Dürr, GRL, accepted]

16. Estimates of global annual-mean radiative forcings for the period from pre-industrial (1750) to present Can radiative forcings be measured at Earth’s surface ? [IPCC, 2001]

17. Changes of Radiative Fluxes and Cloud Effect in the Alps 1995-2002 Longwave cloud effect LCE [Wm -2 ] Year Longwave Downward Rad. LDR [Wm -2 ] Year Shortwave Downward Rad. SDR [Wm -2 ] Year

18. Cloud free Longwave Downward Radiation, Temperature and Humidity t [°C] Temperature Year Absolute Humidity Year u [g m -3 ] Longwave Downward Rad. cloud free Year LDR cf [Wm -2 ]

19. Measurements and GCM model Estimates ECHAM-4 GCM Calculation for 10 % CO 2 Increase LDR + 4.2 Wm -2 + 4.6 Wm -2 SDR - 1.0 Wm -2 - 1.4 Wm -2 Temperature + 0.82 °C + 0.74 °C Abs Humidity + 0.21 g m -3 + 0.20 g m -3 However, the CO 2 increase from 1995 – 2002 is only 12 ppm or 3.3 % ASRB Measurements 1995-2002 The CO 2 Increase from 1980 – 2002 is 35 ppm or 10 %

20.  Clouds strongly modulate shortwave and longwave radiation but they compensate each other on the annual mean  The temperature increase is primarily driven by increasing cloud-free longwave radiation (very high correlation between T and LDR cf )  The total heating radiation is well correlated with temperature and drives the temperature increase  Solar shortwave radiation decreases from 1981-2002 and it is therefore not the cause for the temperature increase Summary