Water vapor and climate change
The amount of water vapor in the atmosphere responds sensitively to changes in
temperature. The amount of water vapor
increases by over 20% for a 3K rise in temperature if
the relative humidity remains approximately constant.
Climate model simulations do predict changes in the distribution of
relative humidity, but the overall change is relatively small.
This has implications for many aspects of
atmospheric dynamics when considering global warming or very warm past climates.
An outstanding challenge involves fully incorporating the effect of
water vapor and latent heat release into theories of how, for example, the
extent of the Hadley cell, the extratropical storm track position, or the
strength of extratropical storms change as climate changes.
Precipitation and its extremes
Given the large increase in atmospheric water vapor with increasing
temperature, it is natural to ask how precipitation changes.
Climate models suggest that both global mean precipitation and the
intensity of precipitation extremes will increase in a warmer climate.
Local decreases in precipitation are also expected in already dry
parts of the world. Quantifying the expected changes in precipitation
and in intense precipitation events is a major challenge
for climate modeling. We are endeavoring to understand the
physical basis for changes in precipitation and its
extremes using extensive simulations of idealized atmospheres, together
with scaling analyses of the underlying equations.
Global warming is expected to cause a poleward shift in extratropical
storm tracks. The change in the intensities of extratropical storms
is less clear, and likely depends on the season or hemisphere under
consideration. The kinetic energy of transient eddies is found to
scale with the dry available potential energy of the mean state in
simulations with an idealized model of the atmosphere. Increased latent heating
in warmer climates does not seem to alter this relation for reasons that
remain unclear. We will attempt to further quantify the changes in the
energy of extratropical storms from very cold to warm climates, and understand if abrupt
changes in the behavior of storm tracks can occur.