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It is shown in this comment that considering the Mauna Loa observation of the atmospheric carbon dioxide concentration and the mean near surface temperature anomalies for the period from the beginning of the seventies to recent years only is, clearly, a source of misinterpretation. If we consider the whole period of available data (1958 - 2004), we obtain results which differ from those presented by Rahmstorf et al. It is also shown that in 1988 when the Intergovernmental Panel of Climate Change (IPCC) of the United Nations and the World Meteorological Organization (WMO) was established there was certainly no correlation between the atmospheric carbon dioxide concentration and the mean near surface temperature anomalies, neither on the annual time scale nor on the monthly time scale.
We present recent observed climate trends for carbon dioxide concentration, global mean air temperature, and global sea level, and we compare these trends to previous model projections as summarized in the 2001 assessment report of the Intergovernmental Panel on Climate Change (IPCC). The IPCC scenarios and projections start in the year 1990, which is also the base year of the Kyoto protocol, in which almost all industrialized nations accepted a binding commitment to reduce their greenhouse gas emissions. The data available for the period since 1990 raise concerns that the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates.