(cr) What role does the sun play for the climate on earth? This can best be answered based on the past when humanity did not yet influence the climate. The large climatic swings between ice ages and the warm periods such as the last 10'000 years are largely due to the position of the sun with respect to the earth. In addition, the sun by itself is not a constant source of energy and many climatic variations were caused by small fluctuations in the solar activity.
Despite the natural variability of the sun it is highly likely that the global warming of the last 50 years is substantially influenced by human activities. This is the conclusion that Dr. Jürg Beer from the EAWAG drew during the parliamentary meeting in December 2002. At the same meeting Dr. Stefan Nowak, the program director of the photovoltaic project of the Federal Department of Energy BFE discussed the potential and limitations of producing electricity by photovoltaic technology. Studies show, that a diversity of renewable energy sources may replace about 20% of the conventional energies at comparable cost. Photovoltaic is most suitable for already built surfaces such as roofs with favorable orientation. More than 15% of the current Swiss electricity consumption may be produced in this way.