¥ Far less water vapor as in lower troposphere because temperatures
are much colder (SVP much less)
¥ Fractional changes in UT WV are
almost as important as in LT WV because temperatures
are much colder
¥ so IR emitted from upper troposphere is
small reducing
outgoing IR to space
¥Climate models generally predict UT WV should increase as climate warms
¥Very challenging to measure UT WV
¥At least indirect inferences that UT WV is increasing
¥Some doubt about the robustness of this
result and its generality