Critical Loads − Link between Science and Policy

Maximilian Posch, Coordination Centre for Effects (CCE), RIVM, PO Box 1, NL-3720 BA Bilthoven, the Netherlands

Presentation: Max Posch.pdf 

Critical loads (and levels) are based on the concept of an ecological threshold. This was discussed, mostly in Canada, in the mid-1970s; and in 1983 a ‘target load’ to aquatic ecosystems of 20 kg of wet sulphate per hectare per year was proposed.

It was in Europe, however, where the concept and basic calculation methods for critical loads have been developed, first under the Nordic Council of Ministers and then for the work under the 1979 LRTAP Convention. While earlier protocols to the Convention were stand-still agreements or required flat-rate emission reductions, the 1994 Sulphur Protocol was the first to consider ecosystem vulnerability in terms of critical loads for the formulation of emission reduction requirements.

The signing of this protocol was a first climax of the work of the (then) Task Force on Mapping Critical Levels/Loads, which was established in 1989 under the WGE of the LRTAP Convention. Under this Task Force, critical load data from individual countries are collected, collated and mapped by the CCE and provided to relevant Convention bodies (CIAM) as well as the European Commission to formulate emission reduction strategies in Europe, e.g. for the 1999 Gothenburg Protocol or the NEC Directive.

This presentation will give an outline of the historical development of the concept of a critical load and the methods and principles to estimate/calculate them. The focus is on sulphur (acidity) and nitrogen. Their past and potential future use in integrated assessment for the design of emission reduction policies will be illustrated.


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