The world’s leading climate scientists have warned there is only a dozen years for global warming to be kept to a maximum of 1.5C, beyond which even half a degree will significantly worsen the risks of drought, floods, extreme heat and poverty for hundreds of millions of people. 
 
 The authors of the landmark report by the UN Intergovernmental Panel on Climate Change (IPCC) released on Monday say urgent and unprecedented changes are needed to reach the target, which they say is affordable and feasible although it lies at the most ambitious end of the Paris agreement pledge to keep temperatures between 1.5C and 2C. 
 
 The half-degree difference could also prevent corals from being completely eradicated and ease pressure on the Arctic, according to the 1.5C study, which was launched after approval at a final plenary of all 195 countries in Incheon in South Korea that saw delegates hugging one another, with some in tears. 
 
 Quick guide What difference would restricting warming to 1.5C make? Show Hide A key finding of the new IPCC report is the dramatic difference that restricting warming to 1.5C above pre industrial levels would have on the global environment. The scientists found: • By 2100, global sea level rise would be 10cm lower with global warming of 1.5C compared with 2C. • Extreme heatwaves will be experienced by 14% of the world's population at least once every five years at 1.5C. But that figure rises to more than a third of the planet if temperatures rise to 2C • Arctic sea ice would remain during most summers if warming is kept to 1.5C. But at 2C, ice free summers are 10 times more likely, leading to greater habitat losses for polar bears, whales, seals and sea birds. 
 
 • If warming is kept to 1.5C, coral reefs will still decline by 70-90% but if temperatures rise to 2C virtually all of the world's reefs would be lost 
 
 
 
 We must reduce greenhouse gas emissions to net zero or face more floods Read more 
 
 “It’s a line in the sand and what it says to our species is that this is the moment and we must act now,” said Debra Roberts, a co-chair of the working group on impacts. “This is the largest clarion bell from the science community and I hope it mobilises people and dents the mood of complacency.” 
 
 Policymakers commissioned the report at the Paris climate talks in 2016, but since then the gap between science and politics has widened. Donald Trump has promised to withdraw the US – the world’s biggest source of historical emissions – from the accord. The first round of Brazil’s presidential election on Sunday put Jair Bolsonaro into a strong position to carry out his threat to do the same and also open the Amazon rainforest to agribusiness. 
 
 The world is currently 1C warmer than preindustrial levels. Following devastating hurricanes in the US, record droughts in Cape Town and forest fires in the Arctic, the IPCC makes clear that climate change is already happening, upgraded its risk warning from previous reports, and warned that every fraction of additional warming would worsen the impact. 
 
 Scientists who reviewed the 6,000 works referenced in the report, said the change caused by just half a degree came as a revelation. “We can see there is a difference and it’s substantial,” Roberts said. 
 
 At 1.5C the proportion of the global population exposed to water stress could be 50% lower than at 2C, it notes. Food scarcity would be less of a problem and hundreds of millions fewer people, particularly in poor countries, would be at risk of climate-related poverty. 
 
 Facebook Twitter Pinterest Attendees take a photo before the opening of the 48th session of the IPCC in Incheon. Photograph: Jung Yeon-Je/AFP/Getty Images 
 
 At 2C extremely hot days, such as those experienced in the northern hemisphere this summer, would become more severe and common, increasing heat-related deaths and causing more forest fires. 
 
 But the greatest difference would be to nature. Insects, which are vital for pollination of crops, and plants are almost twice as likely to lose half their habitat at 2C compared with 1.5C. Corals would be 99% lost at the higher of the two temperatures, but more than 10% have a chance of surviving if the lower target is reached. 
 
 Sea-level rise would affect 10 million more people by 2100 if the half-degree extra warming brought a forecast 10cm additional pressure on coastlines. The number affected would increase substantially in the following centuries due to locked-in ice melt. 
 
 Oceans are already suffering from elevated acidity and lower levels of oxygen as a result of climate change. One model shows marine fisheries would lose 3m tonnes at 2C, twice the decline at 1.5C. 
 
 Sea ice-free summers in the Arctic, which is warming two to three times faster than the world average, would come once every 100 years at 1.5C, but every 10 years with half a degree more of global warming. 
 
 The final tick box is political will Jim Skea 
 
 Time and carbon budgets are running out. By mid-century, a shift to the lower goal would require a supercharged roll-back of emissions sources that have built up over the past 250 years. 
 
 The IPCC maps out four pathways to achieve 1.5C, with different combinations of land use and technological change. Reforestation is essential to all of them as are shifts to electric transport systems and greater adoption of carbon capture technology. 
 
 Carbon pollution would have to be cut by 45% by 2030 – compared with a 20% cut under the 2C pathway – and come down to zero by 2050, compared with 2075 for 2C. This would require carbon prices that are three to four times higher than for a 2C target. But the costs of doing nothing would be far higher. 
 
 “We have presented governments with pretty hard choices. We have pointed out the enormous benefits of keeping to 1.5C, and also the unprecedented shift in energy systems and transport that would be needed to achieve that,” said Jim Skea, a co-chair of the working group on mitigation. “We show it can be done within laws of physics and chemistry. Then the final tick box is political will. We cannot answer that. Only our audience can – and that is the governments that receive it.” 
 
 He said the main finding of his group was the need for urgency. Although unexpectedly good progress has been made in the adoption of renewable energy, deforestation for agriculture was turning a natural carbon sink into a source of emissions. Carbon capture and storage projects, which are essential for reducing emissions in the concrete and waste disposal industries, have also ground to a halt. 
 
 Reversing these trends is essential if the world has any chance of reaching 1.5C without relying on the untried technology of solar radiation modification and other forms of geo-engineering, which could have negative consequences. 
 
 Facebook Twitter Pinterest A nearly ice-free Northwest Passage in the Arctic in August 2016. Photograph: VIIRS/Suomi NPP/Nasa 
 
 In the run-up to the final week of negotiations, there were fears the text of the report would be watered down by the US, Saudi Arabia and other oil-rich countries that are reluctant to consider more ambitious cuts. The authors said nothing of substance was cut from a text. 
 
 Bob Ward, of the Grantham Research Institute on Climate Change, said the final document was “incredibly conservative” because it did not mention the likely rise in climate-driven refugees or the danger of tipping points that could push the world on to an irreversible path of extreme warming. 
 
 The report will be presented to governments at the UN climate conference in Poland at the end of this year. But analysts say there is much work to be done, with even pro-Paris deal nations involved in fossil fuel extraction that runs against the spirit of their commitments. Britain is pushing ahead with gas fracking, Norway with oil exploration in the Arctic, and the German government wants to tear down Hambach forest to dig for coal. 
 
 At the current level of commitments, the world is on course for a disastrous 3C of warming. The report authors are refusing to accept defeat, believing the increasingly visible damage caused by climate change will shift opinion their way. 
 
 “I hope this can change the world,” said Jiang Kejun of China’s semi-governmental Energy Research Institute, who is one of the authors. “Two years ago, even I didn’t believe 1.5C was possible but when I look at the options I have confidence it can be done. I want to use this report to do something big in China.” 
 
 The IPCC global warming report spares politicians the worst details | Bob Ward Read more 
 
 The timing was good, he said, because the Chinese government was drawing up a long-term plan for 2050 and there was more awareness among the population about the problem of rising temperatures. “People in Beijing have never experienced so many hot days as this summer. It’s made them talk more about climate change.” 
 
 Regardless of the US and Brazil, he said, China, Europe and major cities could push ahead. “We can set an example and show what can be done. This is more about technology than politics.” 
 
 James Hansen, the former Nasa scientist who helped raised the alarm about climate change, said both 1.5C and 2C would take humanity into uncharted and dangerous territory because they were both well above the Holocene-era range in which human civilisation developed. But he said there was a huge difference between the two: “1.5C gives young people and the next generation a fighting chance of getting back to the Holocene or close to it. That is probably necessary if we want to keep shorelines where they are and preserve our coastal cities.” 
 
 Johan Rockström, a co-author of the recent Hothouse Earth report, said scientists never previously discussed 1.5C, which was initially seen as a political concession to small island states. But he said opinion had shifted in the past few years along with growing evidence of climate instability and the approach of tipping points that might push the world off a course that could be controlled by emissions reductions. 
 
 “Climate change is occurring earlier and more rapidly than expected. Even at the current level of 1C warming, it is painful,” he told the Guardian. “This report is really important. It has a scientific robustness that shows 1.5C is not just a political concession. There is a growing recognition that 2C is dangerous.” 
 
 ||||| FILE - In this Oct. 26, 2015 file photo, fish swim over a patch of bleached coral in Hawaii's Kaneohe Bay off the island of Oahu. Warmer water is repeatedly causing mass global bleaching events to Earth's... (Associated Press) 
 
 WASHINGTON (AP) — Preventing an extra single degree of heat could make a life-or-death difference in the next few decades for multitudes of people and ecosystems on this fast-warming planet, an international panel of scientists reported Sunday. But they provide little hope the world will rise to the challenge. 
 
 The Nobel Prize-winning Intergovernmental Panel on Climate Change issued its gloomy report at a meeting in Incheon, South Korea. 
 
 In the 728-page document, the U.N. organization detailed how Earth's weather, health and ecosystems would be in better shape if the world's leaders could somehow limit future human-caused warming to just 0.9 degrees Fahrenheit (a half degree Celsius) from now, instead of the globally agreed-upon goal of 1.8 degrees F (1 degree C). Among other things: 
 
 — Half as many people would suffer from lack of water. 
 
 — There would be fewer deaths and illnesses from heat, smog and infectious diseases. 
 
 — Seas would rise nearly 4 inches (0.1 meters) less. 
 
 — Half as many animals with back bones and plants would lose the majority of their habitats. 
 
 — There would be substantially fewer heat waves, downpours and droughts. 
 
 — The West Antarctic ice sheet might not kick into irreversible melting. 
 
 — And it just may be enough to save most of the world's coral reefs from dying. 
 
 "For some people this is a life-or-death situation without a doubt," said Cornell University climate scientist Natalie Mahowald, a lead author on the report. 
 
 Limiting warming to 0.9 degrees from now means the world can keep "a semblance" of the ecosystems we have. Adding another 0.9 degrees on top of that — the looser global goal — essentially means a different and more challenging Earth for people and species, said another of the report's lead authors, Ove Hoegh-Guldberg, director of the Global Change Institute at the University of Queensland, Australia. 
 
 But meeting the more ambitious goal of slightly less warming would require immediate, draconian cuts in emissions of heat-trapping gases and dramatic changes in the energy field. While the U.N. panel says technically that's possible, it saw little chance of the needed adjustments happening. 
 
 In 2010, international negotiators adopted a goal of limiting warming to 2 degrees C (3.6 degrees F) since pre-industrial times. It's called the 2-degree goal. In 2015, when the nations of the world agreed to the historic Paris climate agreement, they set dual goals: 2 degrees C and a more demanding target of 1.5 degrees C from pre-industrial times. The 1.5 was at the urging of vulnerable countries that called 2 degrees a death sentence. 
 
 The world has already warmed 1 degree C since pre-industrial times, so the talk is really about the difference of another half-degree C or 0.9 degrees F from now. 
 
 "There is no definitive way to limit global temperature rise to 1.5 above pre-industrial levels," the U.N.-requested report said. More than 90 scientists wrote the report, which is based on more than 6,000 peer reviews. 
 
 "Global warming is likely to reach 1.5 degrees C between 2030 and 2052 if it continues to increase at the current rate," the report states. 
 
 Deep in the report, scientists say less than 2 percent of 529 of their calculated possible future scenarios kept warming below the 1.5 goal without the temperature going above that and somehow coming back down in the future. 
 
 The pledges nations made in the Paris agreement in 2015 are "clearly insufficient to limit warming to 1.5 in any way," one of the study's lead authors, Joerj Roeglj of the Imperial College in London, said. 
 
 "I just don't see the possibility of doing the one and a half" and even 2 degrees looks unlikely, said Appalachian State University environmental scientist Gregg Marland, who isn't part of the U.N. panel but has tracked global emissions for decades for the U.S. Energy Department. He likened the report to an academic exercise wondering what would happen if a frog had wings. 
 
 Yet report authors said they remain optimistic. 
 
 Limiting warming to the lower goal is "not impossible but will require unprecedented changes," U.N. panel chief Hoesung Lee said in a news conference in which scientists repeatedly declined to spell out just how feasible that goal is. They said it is up to governments to decide whether those unprecedented changes are acted upon. 
 
 "We have a monumental task in front of us, but it is not impossible," Mahowald said earlier. "This is our chance to decide what the world is going to look like." 
 
 To limit warming to the lower temperature goal, the world needs "rapid and far-reaching" changes in energy systems, land use, city and industrial design, transportation and building use, the report said. Annual carbon dioxide pollution levels that are still rising now would have to drop by about half by 2030 and then be near zero by 2050. Emissions of other greenhouse gases, such as methane, also will have to drop. Switching away rapidly from fossil fuels like coal, oil and gas to do this could be more expensive than the less ambitious goal, but it would clean the air of other pollutants. And that would have the side benefit of avoiding more than 100 million premature deaths through this century, the report said. 
 
 "Climate-related risks to health, livelihoods, food security, water supply, human security and economic growth are projected to increase with global warming" the report said, adding that the world's poor are more likely to get hit hardest. 
 
 Princeton University climate scientist Michael Oppenheimer said extreme weather, especially heat waves, will be deadlier if the lower goal is passed. 
 
 Meeting the tougher-to-reach goal "could result in around 420 million fewer people being frequently exposed to extreme heat waves, and about 65 million fewer people being exposed to exceptional heat waves," the report said. The deadly heat waves that hit India and Pakistan in 2015 will become practically yearly events if the world reaches the hotter of the two goals, the report said. 
 
 Coral and other ecosystems are also at risk. The report said warmer water coral reefs "will largely disappear." 
 
 The outcome will determine whether "my grandchildren would get to see beautiful coral reefs," Princeton's Oppenheimer said. 
 
 For scientists there is a bit of "wishful thinking" that the report will spur governments and people to act quickly and strongly, one of the panel's leaders, German biologist Hans-Otto Portner, said. "If action is not taken it will take the planet into an unprecedented climate future." 
 
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 Follow Seth Borenstein on Twitter: @borenbears . His work can be found here . 
 
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 The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute's Department of Science Education. The AP is solely responsible for all content.
– The latest United Nations report on climate change doesn't sugarcoat its findings: Climate change is here, with catastrophic effects, and it is going to get worse. But that doesn't mean it's time to give up: The report from the UN Intergovernmental Panel on Climate Change stresses that the planet will be a much better place both for wildlife and humans if future warming can be limited to a half-degree Celsius—0.9 degrees Fahrenheit—instead of the 1.8 degrees F, or 1 degree C, that governments have agreed to work toward, the AP reports. The world is already 1 degree Celsius warmer than it was in pre-industrial times, and the report warns that there will have to be a massive decrease in carbon emissions by 2030 to have a chance of keeping total warming below 1.5 degrees C. The report, prepared by the world's leading climate scientists, warns that there are only around 12 years left to keep the warming to the lower figure—but if it can be achieved, far fewer people will suffer from food scarcity and water shortages, the Guardian reports. The lower figure also leaves hope that the West Antarctic ice sheet will not enter irreversible melting and at least some of reefs like the Great Barrier Reef will survive. "For some people this is a life-or-death situation without a doubt," says lead author Natalie Mahowald, a Cornell University climate scientist. The panel warns, however, that limiting warming to the lower figure will require a "rapid and far-reaching" transformation of civilization, for which there is "no documented historic precedent," the Washington Post reports.