Impact of a Warmer Climate on the Global Wave Field

Changes in global wave climate and its impacts received only minimal attention in the IPCC Fourth Assessment Report (AR4). Discussions provided are mostly restricted to the long-term variability of the significant wave height based on visual estimates from voluntary observing ships while other components of the wave climate are mostly ignored. Despite some attempts in studying the impact of a warmer climate on the global wave field based on statistical projections, and some recent regional dynamical projections using regional climate models to force wave models, a coherent global modelling study of the future changes in the global wave climate is still lacking.

Tropical and extra-tropical cyclones are the main generating forces behind the global wave field. Recent studies, based on runs with the high resolution (T213; 63 km) version of the ECHAM5 global climate model revealed that in a warmer climate extra-tropical storms will not necessarily get more intense. On the other hand a poleward shift of the extra-tropical storm tracks is expected in both hemispheres. The effects of these changes on the future global wave climate are investigated in the present study. The high-resolution ECHAM5 near-surface wind fields are used to force the wave model WAM and to simulate the global wave climate of two 32-yr periods that are representative for the end of the twentieth (1959-1990) and twenty-first (2069-2100) centuries. The twentieth century period is referred to as the control period. Comparison of control period wave climate with that obtained from the corrected ECMWF reanalysis shows a good agreement and comparison of climate change signals (future-present) reveals changes consistent with poleward shift of extra tropical storm tracks. Further studies using different model/emission scenario combinations are needed to fully assess robustness and uncertainty of these changes.