qThere are significant differences in trends btw the surface and lower troposphere, particularly
in the tropics and
subtropics.
qGlobal trends since 1979 are most positive at the surface,
near zero for
levels between 850 to 300
hPa (1.5 to 8 km) (i.e., troposphere) and negative at 200 hPa (11 km) and above (mostly the stratosphere).
qThe large, negative trends in the stratosphere are attributed to
the combined
effects of ozone depletion
and increased concentrations
of infrared radiating
gases, mainly water vapor
and carbon dioxide.