[en] After intense negotiations, the industrialized countries with the exception of the U.S.A. reached an agreement on the reduction of greenhouse gases. One of the reasons that the U.S.A. would not sign the agreement was that there is no commitments on the part of the developing countries. It is important to increase the engagement of the developing countries in climate issues since otherwise the increase in the emission of greenhouse gases from these countries may be very large. One contribution can be to elucidate the fact that many measures to reduce the emission of greenhouse gases will also help to solve local and regional environmental problems. This is the so-called Clean Development Mechanism, which is also favourable for the industrialized countries, and which is further discussed in this article. The article discusses two studies in which so-called ancillary benefits were calculated for the reduction of CO₂ emissions in Hungary and the Shanxi province of China