Many fluorinated gases have
very high global warming potentials (GWPs) relative to other greenhouse gases, so small atmospheric concentrations can have proportionately large effects on global temperatures.
In
very short form (recognizing that I will write somewhat loosely for purposes of brevity in this setting), Weitzman's central claim is that the probability distribution of
potential losses from
global warming is «fat - tailed», or includes
high enough odds of
very large amounts of
warming (200C or more) to justify taking expensive action now to avoid these low probability /
high severity risks.