The previous CH2018 climate scenarios already showed clear climate trends: more extreme heat, more frequent heavy precipitation, drier summers and winters with less snow. While the qualitative statements have not changed, the quantitative assessments have been updated.
Over Western and Central Europe, the temperature has risen more sharply since 1980 than projected in the regional climate models that form the basis for CH2018. There are two main explanations for this: On the one hand, air quality - worldwide, but also in Europe - has improved significantly since the 1980s, meaning that the concentration of aerosols in the air has decreased. As a result, less sunlight is scattered back, causing the atmosphere to heat up more (brightening effect). This was not directly taken into account in previous models (e.g. Wild, 2012). On the other hand, natural fluctuations in the climate may play a significant role.
In the Climate CH2025 scenarios, observations and models are now better integrated and the modelled temperature trend has been adjusted to reflect actual developments. As a result, the Climate CH2025 scenarios show higher warming than previous projections. In a 3-degree world, this corresponds to approximately 10 to 15 percent more warming than in CH2018.
Climate CH2025 is based on CH2018 and expands on it with longer measurement series, improved process understanding and information from new, high-resolution climate simulations that allow for convection. The current MeteoSwiss reference period 1991–2020 was also used. In addition, detailed information on heavy precipitation and heat in urban areas, among other things, was compiled. With the introduction of global warming levels, it is now possible to link political climate targets directly to climatic impacts.
References:
Schumacher, D.L., Singh, J., Hauser, M. et al. Exacerbated summer European warming not captured by climate models neglecting long-term aerosol changes. Commun Earth Environ 5, 182 (2024). https://doi.org/10.1038/s43247-024-01332-8
Wild, M. (2012). Enlightening global dimming and brightening. Bulletin of the American Meteorological Society, 93(1), 27-37.
