The extremely warm summer of 2018 in Sweden – set in a historical context

Abstract

Abstract. Two long-lasting high-pressure systems in summer 2018 led to persisting heatwaves over Scandinavia and other parts of Europe and an extended summer period with devastating impacts on agriculture, infrastructure, and human life. We use five climate model ensembles and the unique 263-year-long Stockholm temperature time series along with a composite 150-year-long time series for the whole of Sweden to set the latest heatwave in the summer of 2018 into historical perspective. With 263 years of data, we are able to grasp the pre-industrial period well and see a clear upward trend in temperature as well as upward trends in five heatwave indicators. With five climate model ensembles providing 20 580 simulated summers representing the latest 70 years, we analyse the likelihood of such a heat event and how unusual the 2018 Swedish summer actually was. We find that conditions such as those observed in summer 2018 are present in all climate model ensembles. An exception is the monthly mean temperature for May for which 2018 was warmer than any member in one of the five climate model ensembles. However, even if the ensembles generally contain individual years like 2018, the comparison shows that such conditions are rare. For the indices assessed here, anomalies such as those observed in 2018 occur in a maximum of 5 % of the ensemble members, sometimes even in less than 1 %. For all of the indices evaluated, we find that the probability of a summer such as that in 2018 has increased from relatively low values in the pre-industrial era (1861–1890, one ensemble) and the recent past (1951–1980, all five ensembles) to higher values in the most recent decades (1989–2018). An implication of this is that anthropogenic climate change has strongly increased the probability of a warm summer, such as the one observed 2018, occurring in Sweden. Despite this, we still find such summers in the pre-industrial climate in our simulations, albeit with a lower probability.

Future changes of circulation types and their effects on surface air temperature and precipitation in the SMHI large ensemble

“…For example, heatwaves over Scandinavia are often associated with persistent blocking situations which correspond to the CT1 in our study. In fact, the extreme heatwave in summer 2018 which had devastating impacts on different sectors of society (Wilcke et al 2020) had one third of all days between May and July assigned to the CT1 equivalent in a set of 10 CTs obtained from ERA5 reanalysis (Hersbach et al 2020) using SANDRA (not shown). Our analysis revealed a significant increase in CT1 frequency during summer and hence indicates that heatwaves will become more frequent over Scandinavia.…”

“…The first one involves changes in frequency of the individual CTs; having, e.g., more or less westerly circulation situations or more or less blockings over a specific domain can have strong implications for regional and local weather and climate conditions. This includes consequences for extremes like cold winters (Cattiaux et al 2010) or warm summers (Wilcke et al 2020). The second aspect includes changes in the link between circulation and local climate, or the "effect" that the individual CTs have on dependent variables like surface temperature or precipitation rates.…”

Natural hazards and extreme events in the Baltic Sea region

“…The Baltic Sea area is generally less exposed to severe heat spells compared with regions such as the southern parts of Europe. During the last decade, however, record-breaking heat waves have hit the region, namely, those in 2010, 2014(Sinclair et al, 2019Liu et al, 2020;Baker-Austin et al, 2016;Wilcke et al, 2020). Because people living in the Baltic Sea region are adapted to a relatively cool climate, high summertime temperatures pose a significant risk to health in the current climate (e.g.…”

Green and renewable resources: an assessment of sustainable energy solution for Far North Queensland, Australia

“…In addition, the continual ocean acidification because of carbon uptake (the ocean surface water pH level has been falling at a range of 0.017–0.027 pH units per decade since the 1980s) including oxygen vanished with a loss of 0.5–3.3% between 1970 and 2010 from the ocean surface to 1000 m [ 20 ]. Numerous peer-reviewed literature has already been reported about the weather extremes around the world, such as droughts in South Africa [ 21 ], extreme heatwaves in Sweden [ 22 ], excessive 6-day rainfall in Bangladesh [ 23 ] and hurricanes in the Caribbean [ 24 ]. These extreme weather events are due to the global surface temperature increment which are likely to be the results of the accumulation of GHG (carbon di-oxide, nitrous oxide, methane, halocarbons) in the atmosphere [ 25 ].…”