Detection of Climate Change and Attribution of Causes

When the first full assessment report of the Intergovernmental Panel on Climate Change (IPCC) was presented at the Second World Climate Conference (SWCC) in Geneva, Switzerland, in late October 1990, the Ministerial Conference at the end of SWCC in early November 1990 asked for a United Nations Framework Convention on Climate Change (UNFCCC) to be ready for the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro, Brazil, in June 1992. At this time the urgency for action was not based on the detection of anthropogenic climate change in observations of climate parameters but merely on the following three pillars of argumentation:

1. Rise of long-lived greenhouse gas concentrations: nearly 0.5 percent per year for carbon dioxide (CO2), about 1.0 percent per year for methane (CH4) and 0.25 percent per year for nitrous oxide (N2O) for the 1980s.

2. High correlation between CO2 and CH4 concentrations on one side and temperature at precipitation formation on the other, detected in Antarctic ice cores, dating back until about 160,000 years. CO2 and CH4 concentrations were derived from air bubbles within the ice core at station Vostok on the West Antarctic Plateau.

3. Projections of climate change in general circulation models of the atmosphere, which were run under conditions of enhanced CO2 concentration with a shallow ocean mixed layer as lower boundary. The sensitivity to CO2 concentration increases was judged to lie between 1.5 and 4.5°C mean global warming at the surface for a doubling of pre-industrial CO2-concentration from 280 to 560 ppmv.

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