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

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

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

Temperature increase in Central Europe versus Northern Hemisphere [P. Jones Tave ( ) minus Tave ( ) Tave ( ) minus Tave ( )

Temperature CE and NH versus Alps

ASRB - Network Alpine Surface Radiation Budget in Switzerland ANETZ Stations

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

ASRB-Station Gornergrat

ASRB - Station VSF Weissfluhjoch

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

Decreasing shortwave downward radiation SDR Rather decreasing SDR trend since 1981, except if Summer 2003 is included

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

Longwave Cloud Effect Shortwave Downward Rad. Longwave Downward Rad. Total Heating Rad. Longwave Upward Rad. (or Temperature) Total Net Radiation Radiation Budget

Very high correlation between cloud-free LDR cfr and Temperature and Humidity Cloud-free Longwave Downward Rad. Longwave Upward Rad. (or Temperature) 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]

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]

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]

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

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 ]

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

 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 and it is therefore not the cause for the temperature increase Summary