The existence or non-existence of the so-called atmospheric greenhouse effect continuously dominates the extremely emotional discussion about a human impact on global warming. Most scientists agree with the fundamental greenhouse theory, but like their opponents they are missing a reliable experimental verification of this effect.
Measurements at the open atmosphere are too strongly affected by perturbations to quantify the relatively small contribution of greenhouse gases to local heating of the air or the Earth’s surface. Therefore, we have developed an advanced laboratory set-up, which allows to largely eliminate convection or heat conduction and to reproducibly study the direct influence of greenhouse gases under similar conditions as in the lower troposphere. We measure the additional warming of a pre-heated plate due to back-radiation of the greenhouse gases carbon dioxide, methane and nitrous oxide as a function of the gas concentration, and we derive from the observed warming the radiative forcing of these gases. The measurements are well confirmed by radiation transfer calculations and underline that there exists no