Environmental Engineering Reference
In-Depth Information
on the NCAR Community Climate Model radiation code, but employing
an idealized vertical profile of temperature and humidity. The general ap-
proach is the same as that outlined in Chapter 4 of Pierrehumbert (2010).
The temperature profile consists of a moist adiabat patched on to an isother-
mal stratosphere. The stratospheric water vapor mixing ratio was assumed
vertically uniform, at a value equal to the mixing ratio at the tropopause.
For the case of fixed water vapor content (no water vapor feedback) the tro-
pospheric water vapor mixing ratio was held fixed at a value corresponding
to 50% relative humidity
computed for the unperturbed temperature
. For
the case including water vapor feedback, the mixing ratio was allowed to
increase with temperature so as to hold the tropospheric relative humidity
fixed at 50%. In both cases, the radiation calculation was done for clear-
sky conditions.
4.5 TEMPERATURE EXTREMES
The steps of the analysis, which we applied to the grid point scale,
are:
1. From the 22 CMIP3 models' runs available for 20C3M we
extract annual values of average TAS in June-July-August and
December-January-February.
2. We then form anomalies from the 1971-2000 mean and compute
their distribution (i.e., a set of quantiles).
3. We choose a high quantile (95%, 100%) as benchmark against
which to evaluate the change in likelihood of exceedances in a
warmer climate.
4. We then superimpose spatial patterns of change in seasonal
average temperature derived through pattern scaling for a
series of representative changes in global average temperature.
(Pattern scaling gives us a robust geographical pattern of
seasonal temperature changes that scales linearly with values of
global average temperature.) For each choice of global average
temperature change, this will shift uniformly the quantiles of the
distribution to the right. In our example below we choose additive
patterns corresponding to 1°C, 2°C, and 3°C global average
warming.
5. We finally compute what fraction of the newly derived distribution
lays to the right of the chosen threshold/benchmark.
