In 2014, the Intergovernmental Panel on Climate Change [IPCC] published the Synthesis of the 5th Assessment Report. The results of their investigations are stated very clearly. Warming of the climate system is unequivocal. The atmosphere and the ocean have warmed, the amounts of snow/ice have diminished, and the sea level has risen. In addition, the mean surface temperature in 2014, based on global measurements, is the highest in modern record (since 1880, from GISS/NASA). The main reason for this warming is extremely likely due to the human influence on the climate system, essentially caused by anthropogenic emissions of greenhouse gases. Continued emissions of these gases will lead to further warming and long-lasting changes in all components of the climate system. As a consequence, an international agreement leading to a global reduction of greenhouse gas emissions is urgently needed.
Up to now, so-called climate critics continuously question the additional greenhouse effect. Climate modelling is a difficult task and these models can only describe the Earth system in an approximate way. For example the consideration of the influence of clouds and aerosols in the atmosphere leads to relatively large variations in the calculated warming.
However, simulations with climate models have shown that, by taking into account the increase of atmospheric greenhouse gases, the warming of the Earth system can be well reproduced. When excluding the change in greenhouse gas concentrations, these climate models show virtually no warming of the Earth system for the last fifty years. The IPCC report presents many additional arguments why today´s climate models are more accurate.
Certainly some of the numerical descriptions of the physical processes in climate models can still be discussed for further improvement. But, it is frustrating that climate critics are sceptical about some parts of the climate models which are already proven in detail. Radiative transfer in the atmosphere is a good example of this.
This theory is well developed at an international level. All experts in this research field are convinced that we fully understand the radiative transfer in the atmosphere. The radiative forcing by greenhouse gases in the atmosphere is real. One proof of this is the fact that we are able to determine with high accuracy temperature and trace gas concentrations in the atmosphere from satellite remote sensing. Without knowing the radiative transfer in the atmosphere well this would be not possible.