Uncertainties in local and regional climate scenarios

A climate scenario is not the same as a “forecast”, but rather a possible climate development based on factors known to influence the climate. Several sources of uncertainty are influencing regional and local climate scenarios:

• Internal variations in the climate system lead to natural unpredictable variability. In our region there are large natural climate variations both from year-to-year, but also on larger time-scales.
• Uncertainties concerning changes in climate forcings:
  • Natural forcings: Solar radiation, volcanic activity
  • Anthropogenic emissions of greenhouse gases and aerosols
• Weaknesses in the global climate models
  • Imperfect knowledge on forcings and physical processes
  • Insufficient description of physical processes
  • Too low spatial resolution
• Weaknesses in the downscaling techniques (both concerning dynamical and empirical downscaling).

Different global climate models and different downscaling techniques give different projections, particularly for precipitation. The uncertainties in local and regional estimates are substantially larger than for the global mean given by the global climate models.