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The summer of 2018 was an extraordinary season in climatological terms for northern and central Europe, bringing simultaneous, widespread, and concurrent heat and drought extremes in large parts of the continent with extensive impacts on agriculture, forests, water supply, and the socio-economic sector. Here, we present a comprehensive, multi-faceted analysis of the 2018 extreme summer in terms of heat and drought in central and northern Europe, with a particular focus on Germany. The heatwave first affected Scandinavia in mid-July and shifted towards central Europe in late July, while Iberia was primarily affected in early August. The atmospheric circulation was characterized by strongly positive blocking anomalies over Europe, in combination with a positive summer North Atlantic Oscillation and a double jet stream configuration before the initiation of the heatwave. In terms of possible precursors common to previous European heatwaves, the Eurasian double-jet structure and a tripolar sea surface temperature anomaly over the North Atlantic were already identified in spring. While in the early stages over Scandinavia the air masses at mid and upper levels were often of a remote, maritime origin, at later stages over Iberia the air masses primarily had a local-to-regional origin. The drought affected Germany the most, starting with warmer than average conditions in spring, associated with enhanced latent heat release that initiated a severe depletion of soil moisture. During summer, a continued precipitation deficit exacerbated the problem, leading to hydrological and agricultural drought. A probabilistic attribution assessment of the heatwave in Germany showed that such events of prolonged heat have become more likely due to anthropogenic global warming. Regarding future projections, an extreme summer such as that of 2018 is expected to occur every 2 out of 3 years in Europe in a + 1.5 ∘ C warmer world and virtually every single year in a + 2 ∘ C warmer world. With such large-scale and impactful extreme events becoming more frequent and intense under anthropogenic climate change, comprehensive and multi-faceted studies like the one presented here quantify the multitude of their effects and provide valuable information as a basis for adaptation and mitigation strategies. [ABSTRACT FROM AUTHOR]

The summer of 2018 was an extraordinary season in climatological terms for northern and central Europe, bringing simultaneous, widespread, and concurrent heat and drought extremes in large parts of the continent with extensive impacts on agriculture, forests, water supply, and socio-economic sector. We present a comprehensive, multi-faceted analysis of the 2018 extreme summer in terms of heat and drought in central and northern Europe with a particular focus on Germany. The heatwave first affected Scandinavia by mid-July, shifted towards central Europe in late July, while Iberia was primarily affected in early August. The atmospheric circulation was characterized by strongly positive blocking anomalies over Europe, in combination with a positive summer North Atlantic Oscillation and a double jet stream configuration before the initiation of the heatwave. In terms of possible precursors common to previous European heatwaves, the Eurasian double jet structure and a tripolar sea-surface temperature anomaly over the North Atlantic were identified already in spring. While in the early stages over Scandinavia the air masses at mid- and upper-levels were often of remote, maritime origin, at later stages over Iberia the air masses had primarily a local to regional origin. The drought affected Germany the most, starting with warmer than average conditions in spring, associated with enhanced latent heat release that initiated a severe depletion of soil moisture. During summer, a continued precipitation deficit exacerbated the problem, leading to hydrological and agricultural drought. A probabilistic attribution assessment of the heatwave in Germany showed that the prolonged heat has become more likely due to global warming. Regarding future projections, an extreme summer such as this of 2018 is expected to occur every two out of three years in Europe under a 1.5 °C warmer world and virtually every single year under 2 °C of global warming. With such large-scale and impactful extreme events becoming more frequent and intense under anthropogenic climate change, comprehensive and multi-faceted studies like the one presented here quantify the multitude of effects and provide valuable information as basis for adaptation and mitigation strategies. [ABSTRACT FROM AUTHOR]

North Atlantic oceanic and atmospheric variability is central in determining the behavior of surface climate and hence the occurrence of extremes over the Northern Hemisphere, which in turn have huge impacts on societies, economies and environment. The aim of this study is to gain further insight on the evolution of SST and atmospheric circulation patterns in the context of a changing climate.We use the CM2.6 model, which is the latest version of a series of high-resolution global coupled climate models developed by the NOAA Geophysical Fluid Dynamics Laboratory, with a horizontal resolution of 0.1° (roughly equal to 10km) in the ocean, and a coarser resolution of 0.5°in the atmosphere (50km). Two 80-year long experiments are used, a control simulation with constant pre-industrial atmospheric CO2 concentrations (CR) and a run with CO2 increasing 1% per year until doubling in year 70 and held constant thereafter (2xCO2). We apply Self-Organizing Maps (SOMs), a topology preserving clustering algorithm, to obtain SST and geopotential height (gph500) patterns and we evaluate the model against observations and reanalysis data. We find that the model reproduces the observed patterns very well, even with the use of an objective clustering technique.We then look at changes in frequency and persistence of the patterns in the 2xCO2 run. As expected, the SST response to the CO2 doubling is much more straightforward than the atmospheric response. However, there are patterns in both fields that differ in frequency and amplitude under a changing climate, along with some emerging patterns, which cannot be ordered in any of the CR clusters. Among the latter, a wave-like atmospheric pattern is found in summer months that resembles the one associated with severe heatwaves in Europe during the last decades. There are different possible causes behind those emergent atmospheric patterns under increasing CO2, among which the role of the Arctic Amplification and the slowdown of the Atlantic Meridional Overturning Circulation, that are both prominent in recent years and are common features in future scenarios. Both processes are linked to weakening westerlies in summer over the Atlantic sector, favoring quasi-stationary wave-trains and persistent hot-dry extremes over Europe. Those emerging atmospheric patterns will be further examined regarding their SST precursors and their composites of different climate parameters over Europe. [ABSTRACT FROM AUTHOR]