How much assertion becomes too much

Claim: "There are many possible reasons for the current global warming"

There are a number of reasons why it is very likely that current global warming (i.e. over the past 50 years) is primarily due to man-made emissions of greenhouse gases:

  • All known natural factors that influence the climate either act over much longer periods of time (e.g. the shifting of the continents over millions of years or irregularities in the earth's orbit in tens of thousands of year cycles), or they have changed within the past Not significantly changed for decades (radiation intensity of the sun, cosmic radiation, volcanic activities). In any case, no natural climate factor is known so far, the development of which in the recent past could explain the currently observed global warming with known processes.
  • Climate models of the more recent climatic past can only reproduce the current warming if the anthropogenic greenhouse effect is included in the calculation. The natural factors alone would have led to a slight global cooling over the last few decades (Ammann 2007).
  • The observed temperature changes in the atmosphere are similar to those that would be expected in the event of an increased greenhouse effect: For example, the lowest layer of the atmosphere (up to approx. Ten kilometers in altitude) is currently warming while the upper atmospheric layers (over ten kilometers in height) cool down at the same time. Increased solar radiation, on the other hand, would cause all layers of the atmosphere to warm up. In the last few decades, the warming during the night has been stronger than during the day, while increased solar radiation should logically lead to warming during the day (e.g. Meehl 2003).
  • Direct radiation measurements show an increase in the long-wave heat radiation emanating from the earth (Harries 2001) and an increase in the long-wave radiation that hits the earth from the atmosphere when the sky is clear and can only come from greenhouse gases, since solar radiation is short-wave (Stephens et al . 2012) - both can only be explained by the greenhouse effect.

In addition, no reason has ever been given for a significant increase in greenhouse gas concentration Not should lead to warming in the lower atmosphere - which, by the way, would also contradict the generally known physical knowledge and countless scientific experiments.

Accordingly, in its Fifth Assessment Report from 2013/14 (WG I, SPM, Section D.3), the IPCC summarized the current state of research in very clear terms:

"It is extremely likely [i.e. 95-100 percent certain] that human influence has been the main cause of observed warming since the mid-20th century."

Urs Neu / klimafakten.de, October 2011;
last updated: September 2014