to the Vienna Convention in 1985 (WMO, 1985) the situation had not changed very much although the use of full three-dimensional models for off-line tracer advection for use in chemical calculation was just becoming possible.

The Montreal Protocols, which limit the release of CFCs into the atmosphere, were signed in 1987, and the 1989 assessment (WMO, 1989) was input to these protocols. The state of modeling had advanced significantly with the availability of three-dimensional models of the stratosphere with the recognition that some stratospheric chemistry problems, such as the Antarctic ozone hole, were inherently three-dimensional. The Montreal Protocols required that the parties to the protocols to assess the control measures on the basis of available scientific, technical and economic information, at least every four years beginning in 1990. Notable in the first assessment (WMO, 1991) are chapters on the radiative forcing of climate, the role of ozone as a greenhouse gas and an evaluation of the effects of aircraft and rockets on the ozone layer. The expansion of interest of the assessment seems to have required rapid turnarounds so that mostly simplified models were used for the ozone chemistry which had since become extremely complex. Both the 1994 and 1998 Assessments (WMO, 1994; WMO, 1998) are dominated by two-dimensional models, but there were indications that fully three-dimensional models of the coupled climate and stratospheric chemistry were coming online.

The relationship between ozone and the climate problem, wherein ozone is affected by the climate of the atmosphere and in turn affects the climate, indicates the difficulty of the problem and points to the time when common tools will be used for both the Ozone Assessments and the Intergovernmental Panel on Climate Change (IPCC) assessments (below). As long as these remain separate, it appears that only two-dimensional models can, at present, address the full range of purely stratospheric chemistry concerns. As the problems are recognized to be intimately related and mutually dependent, it is expected that the demands on the modeling community for both assessments will converge.

4.2 IPCC

The IPCC was established in 1988 under the joint auspices of the WMO and the UNEP: “to assess the scientific, technical and socio-economic information relevant for the understanding of the risk of human-induced climate change. It does not carry out new research nor does it monitor climate-related data. It bases its assessment mainly on published and peer reviewed scientific technical literature” ( http://www.ipcc.ch/about/about.htm).

The IPCC is organized into three scientific working groups. Only Working Group 1, which is devoted to scientific aspects of the global



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