An enviro economist and Harvard econ prof write in the NYTimes:
What this will mean for future temperatures is hard to pinpoint with precision, but we estimate that without further action to reduce emissions, the planet is on track to see the eventual global average rise by at least 3 degrees Celsius (5.4 degrees Fahrenheit) above preindustrial levels. This is most likely past the point when we will see the melting of the ice sheets in Greenland and West Antarctica, raising sea levels by dozens of feet. But putting too much emphasis on one particular temperature figure is like zeroing in on the year 2047.
What is scarier still is the uncertainty about the truly extreme outcomes. Our own calculations estimate that there is a roughly 5 percent to 10 percent chance that the eventual average temperature could be 6 degrees Celsius higher, rather than 3. What this would mean is outside anyone’s imagination, perhaps even Dante’s. We can obsess about all of these scenarios. A rise of three degrees would be bad enough. But when you factor in the uncertainty, there is even more reason to put global warming on an even more sharply decreasing path.