"The global average temperature in such a case would in the long term settle between 4 to 5 degrees warmer compared to pre-industrial levels," according to the report. "Sea levels would rise 10 to 60 meters (33 to 197 feet), flooding numerous islands and coastal cities such as Venice, New York, Tokyo and Sydney. Such major population centers would have to be abandoned." Johan Rockström, executive director of the Stockholm Resilience Centre and one of the report's co-authors, is quoted as saying, "It may be very difficult or impossible to stop the whole row of dominoes from tumbling over. Places on Earth will become uninhabitable if 'hothouse Earth' becomes the reality. We still do not know if the climate system can be safely 'parked' at 2 degrees."
It all sounds very bad, very bad indeed. And the worst part, needless to say, is the caveat that—despite the science having been settled decades ago—"we still do not know."
Perhaps now is the time to invoke the precautionary principle so beloved by climate activists and concede that our only safe play here is to geo-engineer a stable global-mean-temperature for the Earth, just as professors David Keith (Harvard) and Edward Parson (UCLA) have suggested.
The eco-radicals won't like it, of course. But surely, after thirty years of terrifying everyone with their dying-Earth prophesies, they would not deny us the opportunity to deploy Keith & Parsons' "surprisingly promising" technological fix when the alternative is to drown in our seaboard cities and perish from heatstroke everywhere else.