¥ 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