Climate projections in the coming decades: uncertainty due to natural variability

Future climate change at local and regional scales will result from a combination of human and natural factors. In this talk we show that unpredictable internally-generated climate fluctuations make a substantial contribution to climate trends projected for the next 50 years over North America and Europe. Results are based on large ensembles of simulations with the Community Earth System Model. We will also show that the large-scale atmospheric circulation is responsible for much of the diversity in climate change projections across the individual ensemble members. We conclude by discussing implications for model validation, inter-model comparisons and interpretation of observed climate trends.