Australia's landmass of 7,617,930 square kilometres (2,941,300 sq mi) is on the Indo-Australian Plate. Surrounded by the Indian and Pacific oceans, it is separated from Asia by the Arafura and Timor seas, with the Coral Sea lying off the Queensland coast, and the Tasman Sea lying between Australia and New Zealand. The world's smallest continent and sixth largest country by total area, Australia—owing to its size and isolation—is often dubbed the "island continent", and is sometimes considered the world's largest island. Australia has 34,218 kilometres (21,262 mi) of coastline (excluding all offshore islands), and claims an extensive Exclusive Economic Zone of 8,148,250 square kilometres (3,146,060 sq mi). This exclusive economic zone does not include the Australian Antarctic Territory. Apart from Macquarie Island, Australia lies between latitudes 9° and 44°S, and longitudes 112° and 154°E.
The Great Barrier Reef, the world's largest coral reef, lies a short distance off the north-east coast and extends for over 2,000 kilometres (1,240 mi). Mount Augustus, claimed to be the world's largest monolith, is located in Western Australia. At 2,228 metres (7,310 ft), Mount Kosciuszko on the Great Dividing Range is the highest mountain on the Australian mainland. Even taller are Mawson Peak (at 2,745 metres or 9,006 feet), on the remote Australian territory of Heard Island, and, in the Australian Antarctic Territory, Mount McClintock and Mount Menzies, at 3,492 metres (11,457 ft) and 3,355 metres (11,007 ft) respectively.
Australia's size gives it a wide variety of landscapes, with tropical rainforests in the north-east, mountain ranges in the south-east, south-west and east, and dry desert in the centre. It is the flattest continent, with the oldest and least fertile soils; desert or semi-arid land commonly known as the outback makes up by far the largest portion of land. Australia is the driest inhabited continent; its annual rainfall averaged over continental area is less than 500 mm. The population density, 2.8 inhabitants per square kilometre, is among the lowest in the world, although a large proportion of the population lives along the temperate south-eastern coastline.
Eastern Australia is marked by the Great Dividing Range, which runs parallel to the coast of Queensland, New South Wales and much of Victoria. The name is not strictly accurate, because parts of the range consist of low hills, and the highlands are typically no more than 1,600 metres (5,249 ft) in height. The coastal uplands and a belt of Brigalow grasslands lie between the coast and the mountains, while inland of the dividing range are large areas of grassland. These include the western plains of New South Wales, and the Einasleigh Uplands, Barkly Tableland, and Mulga Lands of inland Queensland. The northernmost point of the east coast is the tropical-rainforested Cape York Peninsula.
The landscapes of the Top End and the Gulf Country—with their tropical climate—include forest, woodland, wetland, grassland, rainforest and desert. At the north-west corner of the continent are the sandstone cliffs and gorges of The Kimberley, and below that the Pilbara. To the south of these and inland, lie more areas of grassland: the Ord Victoria Plain and the Western Australian Mulga shrublands. At the heart of the country are the uplands of central Australia. Prominent features of the centre and south include Uluru (also known as Ayers Rock), the famous sandstone monolith, and the inland Simpson, Tirari and Sturt Stony, Gibson, Great Sandy, Tanami, and Great Victoria deserts, with the famous Nullarbor Plain on the southern coast.
The climate of Australia is significantly influenced by ocean currents, including the Indian Ocean Dipole and the El Niño–Southern Oscillation, which is correlated with periodic drought, and the seasonal tropical low-pressure system that produces cyclones in northern Australia. These factors cause rainfall to vary markedly from year to year. Much of the northern part of the country has a tropical, predominantly summer-rainfall (monsoon). The south-west corner of the country has a Mediterranean climate. The south-east ranges from oceanic (Tasmania and coastal Victoria) to humid subtropical (upper half of New South Wales). The interior is arid to semi-arid.
According to the Bureau of Meteorology's 2011 Australian Climate Statement, Australia had lower than average temperatures in 2011 as a consequence of a La Niña weather pattern; however, "the country's 10-year average continues to demonstrate the rising trend in temperatures, with 2002–2011 likely to rank in the top two warmest 10-year periods on record for Australia, at 0.52 °C (0.94 °F) above the long-term average". Furthermore, 2014 was Australia's third warmest year since national temperature observations commenced in 1910. Water restrictions are frequently in place in many regions and cities of Australia in response to chronic shortages due to urban population increases and localised drought. Throughout much of the continent, major flooding regularly follows extended periods of drought, flushing out inland river systems, overflowing dams and inundating large inland flood plains, as occurred throughout Eastern Australia in 2010, 2011 and 2012 after the 2000s Australian drought.
Australia's carbon dioxide emissions per capita are among the highest in the world, lower than those of only a few other industrialised nations. A carbon tax was introduced in 2012 and helped to reduce Australia's emissions but was scrapped in 2014 under the Liberal Government. Since the carbon tax was repealed, emissions have again continued to rise.
Although most of Australia is semi-arid or desert, it includes a diverse range of habitats from alpine heaths to tropical rainforests, and is recognised as a megadiverse country. Fungi typify that diversity; an estimated 250,000 species—of which only 5% have been described—occur in Australia. Because of the continent's great age, extremely variable weather patterns, and long-term geographic isolation, much of Australia's biota is unique. About 85% of flowering plants, 84% of mammals, more than 45% of birds, and 89% of in-shore, temperate-zone fish are endemic. Australia has the greatest number of reptiles of any country, with 755 species. Besides Antarctica, Australia is the only continent that developed without feline species. Feral cats may have been introduced in the 17th century by Dutch shipwrecks, and later in the 18th century by European settlers. They are now considered a major factor in the decline and extinction of many vulnerable and endangered native species.
Australian forests are mostly made up of evergreen species, particularly eucalyptus trees in the less arid regions; wattles replace them as the dominant species in drier regions and deserts. Among well-known Australian animals are the monotremes (the platypus and echidna); a host of marsupials, including the kangaroo, koala, and wombat, and birds such as the emu and the kookaburra. Australia is home to many dangerous animals including some of the most venomous snakes in the world. The dingo was introduced by Austronesian people who traded with Indigenous Australians around 3000 BCE. Many animal and plant species became extinct soon after first human settlement, including the Australian megafauna; others have disappeared since European settlement, among them the thylacine.
Many of Australia's ecoregions, and the species within those regions, are threatened by human activities and introduced animal, chromistan, fungal and plant species. All these factors have led to Australia's having the highest mammal extinction rate of any country in the world. The federal Environment Protection and Biodiversity Conservation Act 1999 is the legal framework for the protection of threatened species. Numerous protected areas have been created under the National Strategy for the Conservation of Australia's Biological Diversity to protect and preserve unique ecosystems; 65 wetlands are listed under the Ramsar Convention, and 16 natural World Heritage Sites have been established. Australia was ranked 3rd out of 178 countries in the world on the 2014 Environmental Performance Index.