Nature's tolerance of higher temperatures clearly has its limits. The worst bleaching event on record has left 22 per cent of the Great Barrier Reef's corals dead, with the government agency overseeing the area predicting "there will probably be some further mortality". Species under threat Nature is under siege on other fronts. The number of nationally threatened species and ecological communities has risen more than one-quarter since 2000, according to the Australian Conservation Foundation, citing official data. There's been a near-quadrupling of threatened ecological communities to 78 just in the past 16 years, while the number of threatened fauna has risen more than half. A worse fate has befallen the Bramble Cay melomys, which was the only mammal species endemic to the Great Barrier Reef. University of Queensland researchers blame the rodent-like animal's extinction on rising sea levels affecting its Torres Strait island home, making it the first known mammal extinction from human-induced climate change.

Emissions impossible? The Turnbull government has made much of Australia being on track to "easily meet and beat" the country's goal of cutting 2000-level carbon emissions by 5-25 per cent by 2020. Less appreciated is the fact that by the end of the decade, annual emissions are headed for 577 million tonnes of carbon-dioxide equivalent - or about 6 per cent above 2000 levels. As the Grattan Institute notes in its recent report, Australia is within reach of the lower end of the 2020 target thanks in large part to 128 MT in credits for beating its first target under the Kyoto Protocol in 2008-2012 during the Rudd-Gillard government. But because emissions are rising - from rising coal-fired power emissions and lately more land-clearing - the challenge of hitting 2030 targets will require a sharper cutback than from today's starting point. Turnbull's 2030 target is an emissions cut of 26-28 per cent on 2005 levels, while Labor's election pledge is 45 per cent and the Greens' 63-82 per cent.

Crunch time According to the Turnbull government, Australia's target will require 900 million tonnes of reduced carbon emissions between 2020 and 2030. Environment Minister Greg Hunt has said existing and planned policies can get there. However, the bulk of the emissions cuts are merely aspirational. The Emissions Reduction Fund has $816 million left in its coffers and no new funding.The Safeguard Mechanism has the architecture to become an emissions trading scheme, but will a re-elected Turnbull have the clout to win over climate sceptics within his ranks to make it effective? Energy productivity plans are without funding or bureaucratic back-up. Hopes for technological gains are harder now the government has stripped $1.3 billion from Australian Renewable Energy Agency and wants the Clean Energy Finance Corp to also fund Great Barrier Reef projects and save South Australia's steel industry. Can clean energy rise fast enough? Carbon emissions from the electricity sector are Australia's biggest source - accounting for about one-third - and they have been rising since the Abbott government scrapped the carbon price in mid-2014. Falling costs of clean energy, though, should squeeze fossil fuels' share of the power sector from 85 per cent last year to 41 per cent by 2040, Bloomberg New Energy Finance estimates. Solar panel costs have dived 80 per cent since 2008 and each doubling of production cuts them another 26 per cent. Wind power costs have halved since 2009 and shrink by 19 per cent at each output doubling.

Kobad Bhavnagri, Bloomberg NEF's Australian head, says the electricity industry will need to be much closer to zero emissions by 2040 if Australia is to be within reach of carbon neutrality by a decade later: "It's much harder to do that for the rest of the economy so the power sector has to punch above its weight." Follow Peter Hannam on Twitter and Facebook.