Scientists working on climate on a daily basis must have been rather astonished by the recent interview with professor Fritz Vahrenholt published by European Energy Review (May 2, 2012). Vahrenholt, chief of RWE Innogy, self-proclaimed climate expert and co-author of the book Die Kalte Sonne (The Cold Sun), claims that “the contribution of CO2 to global warming is being exaggerated”. This claim, however, does not stand up to scientific scrutiny. We assess his ideas in the light of the scientific literature on the role of the sun versus other climate forcing factors. The dominant influence of greenhouse gases follows not only from their basic physical properties, but also from their “fingerprint” in the observed warming. The sun, in contrast, has not exhibited any warming trend over the past 50 years. The sun is thus not responsible for the warming seen during this period. Greenhouse gases in all likelihood are.