Canberra – Australia experienced its third hottest year on record in 2017, when surrounding high sea temperatures delivered a second consecutive summer of devastating coral bleaching on the Great Barrier Reef, officials said on Wednesday.Much of the World heritage-listed Great Barrier Reef off Australia's northeast coast has been left a white graveyard due to unusually high ocean temperatures causing mass bleaching of coral expanses in 1998, 2002, 2016 and 2017.The Australian Bureau of Meteorology said in its annual climate statement on Wednesday the unprecedented bleaching episodes in consecutive summers came as sea surface temperatures around Australia in 2017 were the eighth highest since records began in 1900.The bureau found 2017 was Australia's third hottest year since records began in 1910. The mean temperature of 22.76°C was 0.95°C hotter than the 1961-to-1990 average.But the northeast states of Queensland and New South Wales had their hottest year on record in 2017.Seven of Australia's 10 hottest years have been experienced since 2005, the bureau said.'Extraordinarily hot weather'Australian National University climate change expert Will Steffen said Australia should be concerned about its rising temperature and do more to reduce greenhouse gas emissions."Certainly I'm concerned about this because we've seen two mass bleaching events in a row in 2016 and 2017 on the Great Barrier Reef which has damaged or destroyed significant percentages of one of the world's great eco-systems," Steffen told Australian Broadcasting Corp.Extraordinarily hot weather has persisted in parts of Australia into 2018. Australia's largest city, Sydney, on Sunday experienced its hottest day since 1939, peaking at 47.3°C at Penrith in the western suburbs. In 1939, Sydney's temperature soared to 47.8°C.English cricket captain Joe Root spent Sunday night in a Sydney hospital being treated for dehydration and a stomach illness after playing against Australia that day in oppressive heat at the Sydney Cricket Ground.