In this section, we investigate the relationship between carcass weight of lambs and climate, in an attempt to estimate the variation in the carrying capacity of Icelandic rangelands. The necessary components of a rangeland model are discussed, but lack of suitable data at present prevents the construction of a model. Thus, it has not been possible to predict the effects of the climatic scenarios outlined in Section 1 of this report, but certain general assumptions are made regarding rangeland carrying capacity by considering extreme years and periods.