Climate change and its potential impact on mechanical, hydraulic and chemical conditions

The strategy for managing climate related conditions in SKB ' s safety assessments are based on the notion that it is not possible to predict climate in a 100 000-year time perspective. Instead, the approach in the SR-Can safety assessment was to identify and analyse both moderate climate evolutions as well as extremes within which the climate in Scandinavia may vary. To this end, knowledge on general climate variations in Scandinavia was used to identify characteristic climate domains which in turn were used to build a number of selected climate scenarios. The relevant climate domains for the Forsmark and Laxemar sites in the 100 000-year time perspective are; 1) a temperate climate domain, 2) a peri-glacial climate domain, and 3) a glacial climate domain. Also submerged/non-submerged conditions at the sites are of importance. In the SR-Can safety assessment several climate scenarios were investigated, including a reference evolution based on a repetition of reconstructed conditions for last glacial cycle (the Weichselian glaciation and the Holocene interglacial). For this reconstruction, extensive numerical simulations of ice sheets, isostatic changes, and permafrost were conducted. The resulting scenario showed site-specific timing and duration of the three climate domains and submerged periods for the full glacial cycle. This scenario is not a prediction of a future climate evolution. Instead it is one example of a future evolution that in a realistic and consistent way covers all relevant climate related changes that can be expected in a 100 000-year time perspective. Subsequently, this scenario formed the basis for the construction of additional climate scenarios that were used to analyse the effects of more extreme climate evolutions than during the last glacial cycle. Examples of complementary scenarios are a warmer and wetter climate scenario caused by an increased greenhouse effect, and colder scenarios with deeper permafrost or thicker ice sheets than in the reference case. As expected, the largest impact on the geosphere and a KBS-3 repository at the suggested Swedish sites occur during climate conditions supporting glacial conditions. The peak of impact on the geosphere, in terms of stress changes and increased groundwater flow, occurs when the ice sheet margin passes the sites. During peri-glacial periods, the geosphere and hydrosphere may also be heavily affected by frozen permafrost conditions, which change groundwater flow and composition. Periods of temperate climate conditions, including a suggested future anthropogenically induced warmer and wetter climate in Sweden, are mainly beneficial for geosphere stability and KBS-3 repository safety. (author)