Environmental Engineering Reference
In-Depth Information
any given increase in the level of greenhouse gases in our
atmosphere.
Figure
.
showed that it will take
to
years to learn which end of the range of predictions
we are heading for. We should not wait but instead plan
to start with the average prediction of the temperature
increase and adjust our program over the next
to
years as we learn more and reduce the uncertainties
in the predictions.
I would try for stabilization at no more than double
the preindustrial level which would be about
ppm
of CO
ecomparedwiththe
ppm of the eighteenth
century. That gives a central value prediction of a tem-
perature rise of
F. Many, particularly
in Europe, claim that anything above a temperature
rise of
C or about
C or about
F, which would correspond to
ppm of CO
e, is dangerous. However, there is no
sharp threshold to a danger zone and we are already at
nearly
ppm CO
.Idon
'
t think we can hold things
much below
. As technology
improves, we may be able to do better.
Figure
ppm by the year
.
shows
whathastobedonetomeetdifferentgoals.
I have a second reason for wanting to limit green-
house gases to
ppm. The climate record from both
the Greenland and Antarctic ice cores has examples of
sudden temperature changes of many degrees. The tem-
perature stays high for a while and then goes back down.
Some of these instabilities last for centuries. We do not
understand them and should be careful in our choice of
allowed greenhouse gas concentration. My choice of a
limit of doubling eighteenth-century concentrations is a
personal guess at how high we can go without greatly
increasing the risk of a sudden large change, and
