Potential impacts of major nineteenth century volcanic eruptions on temperature over Cape Town, South Africa: 1834–1899

Improving scientific knowledge of volcanic eruptions and their impact on climate is important for testing and improving climate projection models. Despite substantive work on the impacts of major volcanic eruptions on global to regional scale climate, most studies have focussed on the northern hemisphere, with little information available for the southern hemisphere. Nevertheless, there is emerging evidence suggesting that major volcanic eruptions significantly influence weather patterns and climates of the southern hemisphere. Here we examine the climatic impact of major nineteenth century volcanic eruptions at various temporal scales for southernmost Africa (i.e. Cape Town). The oldest and longest available daily instrumental weather record for southern Africa (the South African Astronomical Observatory record) is used to test possible temperature responses following seven major volcanic eruptions (Cosiguina, 1835; Amargura, 1846; Cotopaxi, 1855; Makian, 1861; Cotopaxi, 1877; Krakatau, 1883; Tarawera, 1886) during the period 1834–1899. Following all the eruptions (for which data are available), a mean negative temperature departure is recorded in Cape Town in the second year post-eruption. The most immediate (first ten months) negative temperature response is noted following the four strongest eruptions. Tarawera, the only SH eruption, recorded the strongest and most immediate (months 1–10) mean negative temperature departure (− 0.54 °C). The importance of investigating post-eruption climatic responses at a seasonal temporal scale is demonstrated; for instance by the identification of cooler than ‘normal’ but extreme unidirectional temperature departures during austral autumn. Similarly, investigations at the monthly temporal scale enabled the identification of an increase in extreme opposing month-to-month temperature variability following such eruptions.