Volkmar Wirth is Professor of Theoretical Meteorology and Atmospheric Physics at the Johannes Gutenberg University Mainz and head of the Institute of Atmospheric Physics at that same university. His main interest is dynamic meteorology, which is concerned with understanding the circulation of the atmosphere. His recent publications deal with the impact of the jet stream on extreme weather and how this might change in a future climate. Prof. Wirth is co-speaker of the collaborative research centre 'Waves to Weather', which deals with the prediction and predictability of weather. He also served as chair of the advisory board of the German Weather Service for several years.

Key messages

(1) It is beyond any reasonable scientific doubt that humans have changed the climate on earth through greenhouse gas emission. This climate change is practically irreversible and will become much more severe in the future if the emission of greenhouse gases is not phased out very quickly.

(2) Anthropogenic climate change materialises through, among other things, a strongly enhanced frequency of extreme events (such as heat waves and heavy precipitation). Such weather extremes will be an increasing problem for human society, health, and the economy. The cost incurred by these man-made problems may soon outweigh the cost of decarbonizing the world economy.

(3) The climate system contains so-called tipping points, which means that passing a certain threshold in global warming will irreversibly push a number of climate subsystems into a new state that human society has not yet experienced. The likelihood of passing such thresholds increases with rising temperatures, and this, again, calls for fast decarbonization.

(4) There are open questions regarding the change of the atmospheric circulation that need to be settled. However, these remaining uncertainties do not detract at all from the urgent need for fast action motivated by the well-established facts formulated in items (1)-(3).