denmor, are you saying you don't know if it's Fahrenheit or Celsius - you just assume it's Celsius? Looks as if you're wrong.
In scientific papers scientists generally use SI units, but if you read about science in popular literature you'll know that US writers generally cater for US audiences and refer to temperature in degrees Fahrenheit.
Anyway, I've checked for myself and in the Prologue (which you can read here by clicking on the book on the Amazon website) it states on page 6 (my bold):
Unless otherwise specified, numbers refer to estimated increases above today's global mean temperature (in degrees Fahrenheit).
Note that the book was first published in 1990 so 'today' would be expected to refer to 1990 global mean temperature temperatures.
Also interesting to read, twenty years on, what they wrote back in the late 1980s. This is the relevant segment from the book:
Seems to be pretty close to what's been happening. Although governments are discussing the issue and making agreements, emissions are still rising world-wide and most scientists these days would agree that we have locked in at least two degrees Celsius of warming.
