To mitigate climate change a renewable energy transition is needed. Existing power systems will need to be redesigned to balance variable renewable energy production with variable energy demand. We investigate the meteorological sensitivity of a highly-renewable European energy system using large ensemble simulations from two global climate models. Based on 3×2000 years of simulated weather conditions, daily wind and solar energy yields, and energy demand are calculated. From this data, 1-, 7- and 14-days events of extreme low renewable energy production and extreme high energy shortfall are selected. Energy shortfall is defined as the residual load, i.e. demand minus renewable production. 1-day low energy production days are characterised by large-scale high pressure systems over central Europe, with lower than normal wind speeds. These events typically occur in winter when solar energy is limited due to short day lengths. Situations of atmospheric blocking lead to long lasting periods of low energy production, such 7- and 14-days low production events peak late summer. High energy shortfall events occur due to comparable high pressure systems though now combined with below normal temperatures, driving up energy demand. In contrast to the low energy production events, 1-, 7- and 14-days high shortfall events all occur mid-winter, locked to the coldest months of the year. A spatial redistribution of wind turbines and solar panels cannot prevent these high-impact events, options to import renewable energy from remote locations during these events are limited. Projected changes due to climate change are substantially smaller than interannual variability. Future power systems with large penetration of variable renewable energy must be designed with these events in mind.@en

Climate model projections of future climate change exhibit a robust increase in Arctic precipitation, which invokes an array of climate effects. Idealized climate model simulations with artificially increased Arctic precipitation rates exhibit cooling of near-surface atmospheric temperatures and sea ice expansion. We show here that this cooling cannot be attributed to increased surface albedo from fresh snow and less absorption of solar radiation by sea ice, but rather to a reduction in upward oceanic heat flux. This reduction in heat flux is due to increased precipitation that leads to fresher ocean surface waters and, hence, to more stable stratification of the upper Arctic Ocean. This stratification results in cooling of the ocean surface and warming of deeper ocean layers. The simulations show that sea ice expansion and surface cooling peak in the Barents Sea, a region that is very sensitive to changes in mixed layer depth, which decreases considerably there. In the context of a warming Arctic, with concurrent 50% increases in precipitation in 2100, this negative feedback is estimated to slow down projected RCP8.5 Arctic warming by up to 2.0°C in winter and sea ice retreat by a maximum of 11% in autumn, although seasonal variations are considerable. @en

Evaporation that becomes precipitation again - over the same area or over land in general - is water that recycles in the atmosphere. Hence, this process is often called moisture recycling. But, exactly how important is land evaporation for land precipitation? For some reason this has always been a rather controversial field of study. Different methods, but especially different definitions of moisture recycling are probably at the base of this problem. Here, I would like to present an overview of about eight years of my own research (including contributions from many co-authors), in which I describe the moisture recycling process from different angles. This presentation will guide you to several new concepts and metrics developed to describe and understand the local to global scale moisture recycling process. Topics that will be discussed include: evaporation vs. precipitation recycling, continental moisture recycling, length scales of moisture recycling vs. regional moisture recycling ratios, oceanic and terrestrial sources, the precipitationshed and the evaporationshed concept, the age of atmospheric water, time scales and residence times, the role of interception and transpiration in moisture recycling. These concepts are appealing and useful to a wide range of applications, for example: estimating consequences of land-use change, understanding of past climates, calculating net water footprints, understanding of extremes (rainfall and droughts), climate model evaluation, and management and governance of the role of ecosystems in the water cycle. However, the concepts and metrics developed in moisture recycling studies can only be useful when correctly applied and carefully interpreted. For example, they do not always necessarily describe causal relations. I hope the work presented here serves as a reference for anyone wanting to make use of moisture recycling concepts in their research. @en