Climate variations and change evident in high-quality climate data for Australia's Antarctic and remote island weather stations

Abstract

High-quality homogeneous rainfall and temperature time series have been developed from observations taken by the Australian Bureau of Meteorology for remote island sites: the subantarctic Macquarie Island, Lord Howe Island in the Tasman Sea, Norfolk Island in the southwest Pacific Ocean, Willis Island in the Coral Sea and Cocos Island in the eastern Indian Ocean. In addition, high-quality monthly temperature time series have been developed for three east Antarctic stations operated by Australia (Davis, Mawson and Casey). The quality control process for developing the high-quality data involved two steps. Firstly, a thorough examination of historical station metadata was conducted, with the aim of reconstructing the history of measurements at all stations. An objective statistical test was then applied to detect possible break points in the data series. Where an inhomegeneity was detected by the statistical test and subsequently confirmed based on metadata (historical information about stations and recordings), adjustment was applied at the monthly timescale (as the size of adjustments generally vary from month to month and from season to season). While annual mean surface temperature at Australian Antarctic stations is characterised by high year-to-year variability, results for the homogenised series indicate an increase in mean annual temperatures at Mawson and Davis by 0.35 °C and 0.40 °C respectively in the period 1958–2009. At Casey the mean annual temperature has decreased by –0.2 °C since the beginning of 1970s. This decreasing trend is not statistically significant and is, most likely, related to the existence of the ozone hole. Annual mean surface temperature at the remote island stations is characterised by a relatively small year-to-year variability with all stations showing a warming trend. The annual mean total temperature increase ranges from 0.3 to 0.6 °C over the period 1950–2009 for Macquarie, Norfolk, Lord Howe and Willis Islands, while at Cocos Island temperature increased by 0.3 °C since 1960. Rainfall declined at most subtropical and tropical sites analysed in this study: 20 mm/decade at Norfolk Island (since 1915), 23 mm/decade at Lord Howe Island (since 1950), 17 mm/decade at Cocos Island (since 1916), while little change was found for Willis Island (an increase of 3 mm/decade since 1924). In percent of the annual mean for the indicated period of measurements, rainfall declined about 15 per cent at Norfolk Island, 9 per cent at Lord Howe Island and 8 per cent at Cocos Island, while it slightly increased (about 2.5 per cent) at Willis Island. In contrast, Macquarie island has experienced a sharp increase in rainfall of 30 mm/decade since 1949 (or about 20 per cent of the annual mean for the whole period of record), suggesting that areas south of Australia may have become wetter over recent decades. The patterns of change are broadly consistent with climate change simulations (Trenberth et al. 2007) under the enhanced greenhouse effect which show general warming and a tendency for rainfall declines in subtropical parts and rainfall increases in the subantarctic