Limiting global warming to 1.5C rather than 2C would likely be the difference between the survival of some Great Barrier Reef coral and its complete decline, according to the latest United Nations assessment of climate change science.

The Intergovernmental Panel on Climate Change special report on the impact of global warming of 1.5C above pre-industrial levels, released in South Korea on Monday, found coral reefs were likely to decline between 70% and 90% if the temperature increased to that level. If global warming reaches 2C, more than 99% of coral reefs were projected to decline.

Scientists said it underlined the need for urgent global action to cut greenhouse gas emissions – including a rapid withdrawal of coal-fired electricity, a shift that would have major implications not only for Australia’s power grid, but one of its largest export industries.

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Professor Ove Hoegh-Guldberg, a coordinating lead author on the report and a coral reefs expert with the University of Queensland, said there was a distinct difference in the amount of coral that would remain under the two warming scenarios.

“Going to 2C and above gets to a point where corals can no longer grow back, or you have annual bleaching events. On the other hand, at 1.5C there’s still significant areas which are not heating up or not exposed to the same levels of stress such that they would lose coral, and so we’re fairly confident that we would have parts of those ecosystems remaining,” he said in a briefing to journalists before the report was made public.

While the report does not break down the impact of warming by regions, Australian scientists highlighted several areas where there were clear differences between 1.5 and 2C. Others included the relative risk of drought in the south, river flows, the retreat of snow and ice in alpine areas and the scale of disruption in fisheries as marine species moved south to cooler waters.

It found it not too late to avoid 1.5C, but time was limited. Global emissions rose 1.6% in 2017 after three years of flatlining. The world is considered on track for between 3 and 4C by 2100.

Reaching the goal would likely involve the use of coal for electricity across the globe being cut by between 59% and 78% by 2030 and 73% and 97% by 2050, compared with 2010 levels.

Professor Peter Newman, from the Curtin University Sustainability Policy Institute and a lead author of a chapter of the report on the global response to the climate change threat, said he expected coal would rapidly phase out of the Australian power grid but the country was yet to appreciate what was in store for exports.

“The kind of exports that we’re having will be phased out. We need to get that in our perceptions of the future – that coal cannot be a major part of our export future. It’s not going to have anything like the ability to compete with solar and wind particularly, and we need to adapt out economy accordingly,” he said. “It is going to happen in India, it’s already happening in China.”

The report is likely to increase pressure on the Australian government to explain how it will meet its pledge of a 26-28% cut in national emissions below 2005 levels by 2030. It has been accused of having no policies to meet the target since walking away from a pledge to introduce a policy to cut emissions from the electricity sector. National emissions have risen each year since former prime minister Tony Abbott abolished the carbon price introduced under Julia Gillard.

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The prime minister, Scott Morrison, has said he was focused on reducing power prices, and would not increase Australia’s emissions target. Labor has pledged to make a 45% cut by 2030, in part by boosting the share of renewable energy to 50%. On Sunday, the Labor leader, Bill Shorten, said: “If you don’t care about doing the right thing by the environment, then you actually have no right to be the government of Australia.”

The IPCC spent two years on the report following a request by the world’s governments at the 2015 climate conference in Paris, where 195 countries signed up to an historic agreement to keep the global temperature rise this century well below 2C and – following urging by low-lying island nations and vulnerable developing countries - to pursue efforts to limit the increase to 1.5C.

Citing more than 6,000 scientific references, the panel found limiting warming to 1.5C would require rapid, far-reaching and unprecedented changes in all aspects of society. It says achieving it would have clear benefits for human health and nature and, compared with 2C, help ensure a more sustainable and equitable society.

It is estimated there has already been 1C of warming, overwhelmingly due to human activities that produce greenhouse gases. The world is already seeing and feeling the consequences, including increased extreme weather, rising sea levels and reducing sea ice cover in the Arctic. At the current rate of warming, the world is considered likely to reach 1.5C warming between 2030 and 2052.

Professor Mark Howden, a review editor for the report and the director of the Australian National University’s Climate Change Institute, said: “We need new technologies, energy efficiency, clean energy sources, less deforestation, better land management, sustainable agriculture and many other things. The good news is there’s actually movement in the right direction in many of those areas, but we need to do more and faster if we are to keep to 1.5C or even 2C.”

Howden said 2C warming would mean significantly increased risk of drought, particularly in Australia’s southern half. Expected reduced rainfall would reduce soil moisture while the higher temperature would increase evaporation, depleting the soil more quickly and more rapidly triggering droughts that would tend to be more intense and last longer. He said river flows in south-east and south-west Australia tended to fall linearly as temperatures increased.

Hoegh-Guldberg said corals on the reef faced not only warming waters but ocean acidification, which slowed the pace at which they could form skeletons, affecting the ability to recover from extreme events. There has been a 26% increase in acidity since the pre-industrial period. “It is a really major change in the way ocean systems are working,” he said. “The problem with ocean codification is it takes about 10,000 years to correct in terms of the ocean receiving alkaline material from the continents … so it is here to stay.”

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Newman gave Australia a varying scorecard in its efforts in responding to the issue compared with other countries. On energy transformation, he said Australia was showing quite rapid progress comparable with the rest of the world due to the disruptive effect of solar and wind energy. On urban systems, there were examples of how to do zero carbon development in place, such as the White Gum Valley in Perth where renewable energy was shared to make housing cheaper, though the approach was yet to be mainstreamed. On the land, there were good signs of reforesting to capture emissions. But on industry and transport, Australia’s performance on emissions was poor.

To reach 1.5C, the report found global emissions would need to fall by about 45% below 2010 levels by and be “net zero” by about 2050. Any remaining emissions would need to be balanced by removing carbon dioxide from the atmosphere.

Going past 1.5C warming – described as “overshooting” – would mean a greater reliance on techniques that remove carbon dioxide from the air. The effectiveness of these techniques is unproven at large scale and may carry significant risks. The IPCC found it meant the decisions made today were critical.





