Authors

• Hermann Harde, Helmut-Schmidt-University, Hamburg, Germany
• Michael Schnell, Ex Academy of Science of GDR, Berlin, Germany

Summary

Fossil fuel emissions are made responsible for a climate emergency with catastrophic consequences for our planet, when worldwide anthropogenic emissions are not rapidly stopped. The basis of these forecasts is the atmospheric Greenhouse Effect (GHE). However, particularly the impact of the different greenhouse gases (GH-gases) on our climate is not really well understood, and even serious scientists question the existence or the size of this effect.

The main reason of these doubts is a missing retraceable verification, although there were continuous trials over the last 120 years to confirm or to refute this effect by more or less simple laboratory experiments. Unfortunately there exist some fake experiments with ostensibly measured temperature increases by CO2 of 10°C or more, on the other hand other experiments cannot confirm any warming by GH-gases, or they explain an observed temperature increase by other effects like convection, conduction or pressure induced effects in a gas column. Direct measurements at the atmosphere are too strongly affected by convection, turbulence or scattering effects to quantify the relatively small contribution of greenhouse molecules to any warming of the air or the Earth’s surface, which is dominated by day-night and seasonal cycles with local variations of 60°C or more.

It is high time to stop the endless speculations about the non-existence or disastrous implications of an atmospheric GHE, and to concentrate on reliable investigations, which allow a serious quantification of this effect.

This article presents first quantitative measurements of the atmospheric greenhouse effect with an advanced experimental set-up, which to a large extent allows to eliminate convection or heat conduction and to reproducibly study the direct influence of greenhouse gases under similar conditions as in the lower troposphere. Different to other experiments we use two plates in a closed housing, a heated plate in an upper position and a cooled plate at the bottom. With the sample gas in the tank the heated plate acts simultaneously as radiation source and as sensitive detector for the back-radiation from GH-gases. In this way, the pure radiation effect of the gases is measured as a direct temperature increase of the upper plate or, alternatively at stabilized temperature, as energy saving of the plate heating.

We have investigated the GH-gases CO2, CH4 and N2O over a wide range of concentration changes up to a factor of 16. Any noticeable impact due to heat conduction can be excluded by control experiments with noble gases. Our measurements show clear response to the GH-gases but also a strong saturation in the temperature rise with increasing concentration, and they are in excellent agreement with detailed radiation transfer calculations.

Our studies also demonstrate that contrary to the often misinterpreted 2nd law of thermodynamics a warmer body can further be heated by absorbing the radiation from a colder body, here the radiation from the cooled plate and a GH-gas. At the same time reveal our theoretical studies the principal difficulties to measure the GH-effect only as increasing temperature of the gas, which in classical set-ups is mainly dominated by indirect effects like heat exchange with the compartment walls, while an important prerequisite for its observation is missing: the GHE is mainly the result of a temperature difference over the propagation path of the radiation and thus the lapse rate in the atmosphere.

From our measurements and their comparison with the calculations we derive the radiative forcing of the gases when doubling their concentrations. This is an important measure for their impact on global warming, when stronger saturation on the absorption bands is observed, but it also serves as a relative measure at lower concentrations. The found forcings are in good agreement with literature values, which to some degree is also the result of calibrating the set-up to the spectral calculations, but which independently reproduce their variation with the concentration of a GH-gas.

The presented measurements and calculations clearly confirm the existence of an atmospheric GHE, but they also demonstrate the only small impact on global warming with increasing GH-gas concentrations, which in any way are apparently dominated by natural emissions. So, there is no reason for panic and climate emergency, instead it is high time to come back to a consolidated climate discussion, which concentrates on facts and also includes the benefits of GH-gases.

Link to the paper: Verification of the Greenhouse Effect in the Laboratory – Hermann Harde