Where We Are, Where We Go: Uncertainties on the Future of the Impact of Energy Systems on Climate

During past years, the attention of scientists, technologists and policymakers has been focused on carbon dioxide as the first actor in the drama of climate change. As a result, attention has been paid to reducing CO2emissions: cutting fossil carbon as a source of energy has been agreed upon as the solution. More recently, water vapor is rising in rank as a GreenHouse Gas (GHG) responsible for the impact on the climate. As a matter of fact, the atmospheric water-vapor concentration is growing at a much higher rate than that of CO2. Also, water vapor is a stronger GHG than CO2, even if its lifetime is much shorter, as it falls as rain on our planet. On the other hand, extreme events are becoming more frequent, especially in some areas of the planet where the atmospheric concentration of water vapor is growing faster. This suggests that both local and global scenarios should be taken under strict control in order to avoid wrong practices, the effect of incorrect decisions, which may worsen the impact of the global system of energy production on climate. An extended use of hydrogen as an energy vector would increase the emission of water vapor: the potential impact on the climate should, thus, be verified. New scenarios must be developed and new models must be used, which link together the atmospheric concentration of CO2and water vapor, so to estimate their combined impact on the climate.