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We have 12 years to limit climate change catastrophe, warns UNJonathan Watts1. The world's leading climate scientists have warned there is only a dozen years for globalwarming to be kept to a maximum of 1.50 C, beyond which even half a degree willsignificantly worsen the risks of drought, floods, extreme heat and poverty for hundreds ofmillions of people.2. The authors of the landmark report by the UN Intergovernmental Panel on ClimateChange (IPCC) released on Monday say urgent and unprecedented changes are needed toreach the target, which they say is affordable and feasible, although it lies at the mostambitious end of the Paris agreement pledge to keep temperatures between 1.50 C and 20C.What difference would restricting warming to 1.5C make?3. "It's a line in the sand and what it says to our species is that this is the moment and wemust act now," said Debra Roberts, a co-chair of the working group on impacts. "This is thelargest alarm bell from the science community and I hope people understand itsimportance."4. The world is currently 10C warmer than preindustrial . levels. Followingdevastating hurricanes in the US, record droughts in Cape Town and forest fires in the Arctic,it is clear that climate change is already happening, and that any additional warming wouldworsen the impact.5. According to the report, at 1.50 C, the proportion of the global population exposed towater stress could be 50% lower than at 20C. Particularly in poor countries, food scarcitywould be less of a problem and hundreds of millions fewer people would be at risk ofclimate-related poverty. But the greatest difference would be to nature. Insects, which arevital for pollination of crops, and plants are almost twice as likely to lose half their habitat at20C compared with 1.50 C. 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 risewould affect 10 million more people by 2100 with the half-degree extra warming.Oceans are already suffering from elevated acidity and lower levels of oxygen as a result ofclimate change. The loss of fisheries will double if the temperature increases by 20C.6. The IPCC maps out some pathways to achieve 1.50 C, with different combinations of landuse and technological change. Reforestation is essential to all of them as are shifts to electrictransport system. In addition, carbon pollution would have to be cut by 45% by 2030.