evidence: 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. [...] "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." [...] 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.