Multiple perspectives on the attribution of the extreme European summer of 2012 to climate change

Summer (June–August, JJA) 2012 was anomalously wet in northern Europe, and anomalously dry in southern Europe. Characterised by a strong negative summer North Atlantic Oscillation (SNAO) pattern, there was a southward and eastward displacement of the jet over Europe, with most storms tracking along the northern flank and across the British Isles (Dong et al. 2013). The wet northern European summer of 2012 presents a stark contrast to the preceding two years of drought in the UK, and is a rare example of groundwater recovery following drought occurring in the summer months (Kendon et al. 2013). 2012 was the wettest summer in the UK since 1912, and the second wettest year overall since 1910. The UK also experienced widespread fluvial flooding (Parry et al. 2013) (note that England is more vulnerable to flooding than other countries, e.g., Crichton 2005). While northern Europe experienced a wet summer in 2012, the season was anomalously dry in Southern Europe. 2012 saw the lowest summer rainfall in Spain since 1928, which, following on from a winter drought, exacerbated summer drought. Such unusual events naturally raise the question of whether the extremes were influenced by climate change. Event attribution provides a number of approaches to quantify whether climate change has made the occurrence of an extreme event more likely. Studies on event attribution are necessarily influenced by the way the event is selected and framed, and the suitability Abstract Summer 2012 was very wet in northern Europe, and unusually dry and hot in southern Europe. We use multiple approaches to determine whether anthropogenic forcing made the extreme European summer of 2012 more likely. Using a number of observationand model-based methods, we find that there was an anthropogenic contribution to the extremes in southern Europe, with a qualitative consensus across all methodologies. There was a consensus across the methodologies that there has been a significant increase in the risk of hot summers in southern Europe with climate change. Most approaches also suggested a slight drying, but none of the results were statistically significant. The unusually wet summer in northern Europe was made more likely by the observed atmospheric circulation pattern