Long-term measurements of the atmospheric carbon dioxide concentration measured at Jubany station indicate a relationship with 'El Niño'

The role of the atmospheric CO2 concentration for the radiative budget of the Earth and its atmosphere was discovered in the 19th century by J. Tyndall, S.A. Arrhenius and, later on, by G.S. Callendar. But only in the second half of the 20th century some systematic and coordinated programmes began to monitor this parameter. The basic criteria of such programmes carried out on a planetary scale are as follows: the measure in the sampling site must be representative for a geographic area as large as possible, scarcely influenced by anthropogenic or natural factors such as large sources and sinks of CO2 in the surroundings, i.e. densely inhabited areas or areas with a very pronounced vegetative cycle, and finally must not be subject to substantial changes in the land use during the investigation period. A second aspect of great importance is tied up to the procedures used in the routine measurements and the precision obtained in the field. The results obtained by sites conveniently placed over the whole planet need to be comparable in order to study sources and sinks, fluxes of greenhouse gases, which are absorbed and released by the biosphere, seas etc. Data collected around the whole planet form the bases for the inverse modelling technique for constraining global and regional budgets of atmospheric trace gases (Mikaloff et al. 2004, Wouter et al. 2004). WMO launched an international program in the seventies last century named GAW (Global Atmospheric Watch), which is the atmospheric module of the Global Climate Observing System (GCOS). The precision requested to participants is at least 0.1 ?mole/moles CO2 (dry air) and this is checked by periodical round robin test coordinated by WMO. Previously the unit ppm by volume has been used. The Data Center is presently the WDCGG (World Data Center for Greenhouse Gases) operated in Tokyo by the Japan Meteorological Agency. Further initiatives by USA led to the establishing of CDIAC (Carbon Dioxide Information Analysis Center) by the Department of Energy of USA at Oak Ridge (Tn) and of the GLOBALVIEW-CO2 by NOAA-GMD at Boulder (Co). The NOAA-GMD at Boulder also acts as a reference Laboratory (CCL, Central CO2 Laboratory) for standards (CO2 in air cylinders ) used for calibrating the scale of the instruments, usually Non-Dispersive-Infra-Red (NDIR) analyzers. The CCL at Boulder uses a very accurate manometric calibration system (Zhao et al. 1997).