"The economic and social cost of losing functionality of all coastal cities is practically incalculable. We suggest that a strategy relying on adaptation to such consequences will be unacceptable to most of humanity; so, it is important to understand this threat as soon as possible. Limiting global temperatures increase to 2 degrees Celsius above the preindustrial level is not enough. Because the last time the Earth warmed by this much - 120,000 years ago - the consequences were disastrous.

"First, our conclusions suggest that a target of limiting global warming to 2 C, which has sometimes been discussed, does not provide safety.

Second, our study suggests that global surface air temperature, although an important diagnostic, is a flawed metric of planetary 'health,' because faster ice melt has a cooling effect for a substantial period."

Third, not only do we see evidence of changes beginning to happen in the climate system, as discussed above, but we have also associated these changes with amplifying feedback processes. There is a possibility, a real danger, that we will hand young people and future generations a climate system that is practically out of their control. We conclude that the message our climate science delivers to society, policymakers, and the public alike is this: we have a global emergency."