Zwei Studien mit überraschendem Ergebnis: Immer weniger Hitzetote, trotz Klimaerwärmung

Im Februar 2018 erschien im Fachblatt Environment International eine wichtige Studie zu den Auswirkungen des Klimawandels auf Todesfälle. Ein 22-köpfiges Autorenteam um Ana Vicedo-Cabrera untersuchte Trends bei Todesfällen im Zusammenhang mit Hitzewellen und Kältephasen an 305 Orten in insgesamt 10 Ländern. Das Resultat war überraschend: In fast allen Ländern gab es weniger Hitzetote. Bei den Kältetoten war das Ergebnis uneinheitlich: In einigen Ländern gab es mehr, in anderen weniger, in wiederum anderen blieb der Anteil konstant. Auszug aus dem Abstract:

Heat-related AFs [attributable mortality fractions] decreased in all countries (ranging from 0.45–1.66% to 0.15–0.93%, in the first and last 5-year periods, respectively) except in Australia, Ireland and UK. Different patterns were found for cold (where AFs ranged from 5.57–15.43% to 2.16–8.91%), showing either decreasing (Brazil, Japan, Spain, Australia and Ireland), increasing (USA), or stable trends (Canada, South Korea and UK). Heat-AF trends were mostly driven by changes in exposure-response associations due to modified susceptibility to temperature, whereas no clear patterns were observed for cold. […]

Our findings suggest a decrease in heat-mortality impacts over the past decades, well beyond those expected from a pure adaptation to changes in temperature due to the observed warming. This indicates that there is scope for the development of public health strategies to mitigate heat-related climate change impacts. In contrast, no clear conclusions were found for cold. Further investigations should focus on identification of factors defining these changes in susceptibility.

Im Mai 2018 folgte dann noch eine Studie einer Gruppe um Daniel Oudin Åström im International Journal of Biometeorology. Die Forscher werteten Daten aus Stockholm für die letzten 100 Jahre aus und fanden ebenfalls trotz Klimaerwärmung einen Rückgang von Hitzetoten. Der Anteil der Kältetoten blieb jedoch über die Zeit stabil – trotz Temperaturanstieg im letzten Jahrhundert. Abstract:

Investigating changes in mortality attributable to heat and cold in Stockholm, Sweden
Projections of temperature-related mortality rely upon exposure-response relationships using recent data. Analyzing long historical data and trends may extend knowledge of past and present impacts that may provide additional insight and improve future scenarios. We collected daily mean temperatures and daily all-cause mortality for the period 1901–2013 for Stockholm County, Sweden, and calculated the total attributable fraction of mortality due to non-optimal temperatures and quantified the contribution of cold and heat. Total mortality attributable to non-optimal temperatures varied between periods and cold consistently had a larger impact on mortality than heat. Cold-related attributable fraction (AF) remained stable over time whereas heat-related AF decreased. AF on cold days remained stable over time, which may indicate that mortality during colder months may not decline as temperatures increase in the future. More research is needed to enhance estimates of burdens related to cold and heat in the future.