Environmental Engineering Reference
In-Depth Information
same sort of approval process as the climate change
reports to assure the UNFCCC signatories that the scen-
arios are reasonable. The scenarios do not assume the
existence of any mechanisms for greenhouse gas reduc-
tion; the IPCC is not allowed to make such assumptions.
The scenarios are simply alternative economic growth
models that make different assumptions on economic
growth, energy ef
ciency, population, fuel mix, etc. For
example, all the scenarios assume a world economic
growth rate of between
% per year. This does
not seem to be much of a difference in economic growth
in the short term, but over a period of
% and
%
extra economic growth makes world economic output,
energy use, and greenhouse gas emissions more than
twice what they would be with a growth rate of only
years that
%.
Thecalculationsmoveaheadonetimestepatatime.The
model adds a year
s worth of greenhouse gases to the atmos-
phere and calculates what happens to the atmosphere, the
oceans, the clouds, the snow and ice, etc. This answer is the
input for the next time step and so forth on into the future.
'
.
Results
The IPCC cannot yet predict a speci
c number for the
temperature increase by the year
for each of its
scenarios. What they can do is to predict for each scenario
a rough upper and lower limit or range of the temperature
increase, and an average value. The actual increase for
each scenario can lie anywhere in its range with about a
.
The range of outcomes comes from the use of many
climate models that are produced by independent groups.
% probability in AR
and a
% probability in AR
