Future and Past Solar Influence on the Terrestrial Climate

Global warming is one of the main threats to mankind. There is growing evidence that anthropogenic greenhouse gases have become the dominant factor of climate change since about 1970, however the natural factors such as solar variability and volcanic eruptions cannot be neglected on longer time scales. In the previous IPCC assessment (IPCC, 2007) the understanding level of the solar influence on climate was graded as very low. During the last six years a major progress in both, observations and modeling advanced the scientific understanding of solar influence on climate, but still there remain open questions, which should be resolved in the nearest future. The results of the previous FUPSOL project (FUPSOL-I) made a substantial contribution to this process. In the framework of FUPSOL-I we proposed new reconstructions of the solar activity and solar spectral irradiance (SSI) covering 500 years (1600-2100) based on the analysis of the improved 10Be data set and the comprehensive solar radiation code COSI. We developed a fully coupled atmosphere-ocean-chemistry-climate model (AOCCM) and simulated the climate and ozone layer behavior from 1600 up to 2100 by applying spectral solar forcing and all other known forcing data compiled by the project team. The results suggest that the predicted decline of the solar activity in the second half of 21st century might compensate up to 20 % of the greenhouse warming and delay the recovery of the ozone layer. The extensive set of the sensitivity studies improves considerably the discrimination between the contributions of different forcing factors to ozone and climate change. However, based on the analysis of our results and based on recently appeared new observational data and theoretical studies, we conclude that further analyses are needed, in particular with regard to the following issues:

  1. the simulated period (1600-2100) is too short to properly define solar contribution to the future climate;
  2. the climate sensitivity of the applied model to the greenhouse gas increase seems too high;
  3. our AOCCM model has deficiencies in reproducing the observed European winter time climate response to solar forcing;
  4. the analysis of the data representing weather time scale variability was not planned in FUSPOL-I;
  5. there is observational evidence that the solar UV forcing should be stronger than applied in our experiments.

These problems should be addressed to corroborate and refine the conclusions of FUPSOL-I. Therefore, the proposed main goals of FUPSOL-II project are:

  • Analyze the data obtained during FUPSOL-I, concentrating on weather time scale events and their connection to the solar activity;
  • Improve the reconstructions of solar spectral irradiance taking into account new observational data and the results of the climate simulations;
  • Perform a set of sensitivity studies to better understand climate response to greenhouse gases and the response of the European winter time climate to solar forcing;
  • Predict solar forcing factors until 2200 AD and simulate the global climate system behavior from 2000 to 2200 with the improved version of the model.

The proposal is timely because of growing evidence that the Sun is about to enter a new and less active phase of magnetic activity. The present solar maximum will provide new and unprecedented instrumental data, which in combination with long-term reconstructions based on solar activity proxies will form the basis for more reliable model runs of future solar influence on the terrestrial climate. The project is expected to significantly increase our knowledge of the solar influence on the climate system on time scales from short-term weather related to centennial and to elucidate the role of the Sun in future climate change.

Mikhaël Schwander's PhD Thesis takes place in the frame of the FUPSOL-II project. The goal is generate a new weather types time series that will be used to analyze the influence of solar activity on weather patterns in Europe. In the Climatology group, Abdul Malik is also associated to the project by using the climate simulations to investigate the link between solar activity and the Indian Monsoon.

Project team:

Prof. Dr. Werner Schmutz, Dr. Eugener Rozanov, Dr. Alexander Shapiro, Wilnelia Adams (PMOD/WRC Davos)
Prof. Dr. Thomas Peter, Pavle Arsenovic (ETH)
Prof. Dr. Jürg Beer (eawag)
Dr. Christoph Raible, Dr. Stefan Muthers (KUP Bern)
Mikhaël Schwander, Prof. Dr. Stefan Brönnimann (GIUB Bern)



Project duration:

01.01.2014 - 31.12.2016