The Global energy system transition from fossil fuel to hydrogen utilization is described. Environmental benefits of the combustion of hydrogen are reported. World carbon emissions from fossil fuel are schematized in connection with the opportunities of using hydrogen. The atomic hydrogen/carbon ratio and chemical properties of hydrogen are described. Pollutants of the energy system in our planet and hydrogen production technologies are presented. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.