Australia experienced its third-warmest year on record in 2017, and the first-ever recorded instance of two back-to-back bleaching events on the Great Barrier Reef.
The Bureau of Meteorology released the startling data in the Bureau’s annual climate statement. Speaking at the event, Dr. Karl Braganza, Head of Climate Monitoring at the Bureau of Meteorology, said that 2017’s national mean temperature was 0.95 °C warmer than the 1961–1990 average.
“Despite the lack of an El Niño—which is normally associated with our hottest years—2017 was still characterised by very warm temperatures. Both day and night-time temperatures were warmer than average; particularly maximum temperatures, which were the second-warmest on record,” he said.
“Seven of Australia’s ten warmest years have occurred since 2005 and Australia has experienced just one cooler than average year—2011—in the past decade.”
The warmest months of 2017 were March, July, August, October and December — which all ranked in top ten mean temperatures for those month, meaning they were recorded across the average of day and night time temperatures. The daytime temperatures over the year were the second warmest on record, at 1.27 degrees above the 1961-1990 average. All capital cities recorded warmer than average temperatures, with the exception of Perth, posting close to average data.
2017 was a year of mixed results for rainfall, consistent with the neutral El Niño — La Niña conditions, meaning that Australia’s climate was not being influenced by either an El Niño or La Niña event for the majority of the year, but a minor El Niño effect was present in the final three months.
Dr. Braganza said the rainfall data was reflective of these circumstances, with fairly dry conditions were felt throughout the middle of the year, but above average rainfall recorded in many areas for the final three months of the year, associated with a minor El Niño effect during this period.
Sea surface temperatures for the oceans around Australia were well above average in 2017, however.
Prolonged high temperatures around the Great Barrier Reef over Summer and early Autumn caused mass coral bleaching during March, forming the second consecutive year of bleaching following the 2016 event, and the only recorded instance of two back-to-back bleaching events on record. The Bureau noted that no mass bleaching events were ever recorded until the 1980s, neither in empirical records or testimony from oral histories of traditional owners.
Dr. Braganza said that the signal of climate change was discernible in the 2017 temperature data, and that the year’s records were very close to global trends, which is not always the case –Australia’s unique circumstance as an island continent precipitates a larger range of weather extremes than many other countries.
“For the extreme heat events, Australia is one country where you really can see the signal of global warming on heatwaves,” he said.
“Australia has warmed by around a degree, close to the anomaly or the departure from average. 2017 [‘s data] is actually consistent with how much Australia has warmed. So we saw that across the land surface temperatures and in the ocean surrounding Australia, they have both warmed by a similar amount — and this is consistent with global warming as well,” he said.
“This means that odds favour warmer-than-average temperatures more than in the past, and that’s what we’ve seen when you look at temperatures since the late 1980s and 90s. It also means that when conditions are favourable — such as when you have an El Niño, or when rainfall is lower over the Australian continent –we won’t just get warmer than average conditions, we actually start to push into record breaking events. So that change in frequency, or the probability of how warm temperatures are going to be from one year to the next — is certainly evident in the data that we have.”
The Bureau expects reasonable rainfall conditions over the next three months, consistent with light La Niña conditions in Pacific, with a 60-70 percent likelihood of wetter than average conditions for parts of the east coast, and Western Australia. Odds favour cooler than average conditions for parts of the continent, higher rainfall along the east coast and Western Australia, but warmer than average temperatures likely for the southern coastal region, including Perth, Adelaide, Melbourne and Tasmania.