Radiative forcing - measured at Earth's surface - corroborate the increasing greenhouse effect
Article first published online: 6 FEB 2004
Copyright 2004 by the American Geophysical Union.
Geophysical Research Letters
Volume 31, Issue 3, February 2004
How to Cite
2004), Radiative forcing - measured at Earth's surface - corroborate the increasing greenhouse effect, Geophys. Res. Lett., 31, L03202, doi:10.1029/2003GL018765., , , , and (
- Issue published online: 6 FEB 2004
- Article first published online: 6 FEB 2004
- Manuscript Accepted: 23 DEC 2003
- Manuscript Revised: 3 DEC 2003
- Manuscript Received: 3 OCT 2003
 The Intergovernmental Panel of Climate Change (IPCC) confirmed concentrations of atmospheric greenhouse gases and radiative forcing to increase as a result of human activities. Nevertheless, changes in radiative forcing related to increasing greenhouse gas concentrations could not be experimentally detected at Earth's surface so far. Here we show that atmospheric longwave downward radiation significantly increased (+5.2(2.2) Wm−2) partly due to increased cloud amount (+1.0(2.8) Wm−2) over eight years of measurements at eight radiation stations distributed over the central Alps. Model calculations show the cloud-free longwave flux increase (+4.2(1.9) Wm−2) to be in due proportion with temperature (+0.82(0.41) °C) and absolute humidity (+0.21(0.10) g m−3) increases, but three times larger than expected from anthropogenic greenhouse gases. However, after subtracting for two thirds of temperature and humidity rises, the increase of cloud-free longwave downward radiation (+1.8(0.8) Wm−2) remains statistically significant and demonstrates radiative forcing due to an enhanced greenhouse effect.