Environmental Engineering Reference
In-Depth Information
per year) although
there is year-to-year
variability in growth
rates.” The IPCC
forecasted that, on
present trends, this
century would see a
rise in global aver-
age temperature of
between 1.8˚C and
4˚C by 2100.
The
stabilization
challenge
The global average
temperature rise has
already risen by near-
ly one degree centi-
grade above the pre-
industrial level. And,
even if from today
onwards no further
GHGs were emit-
ted, the momentum
of emission increases
in the recent past is
bound to carry us on to a two-degree increase. The aim, however, is to
stop the warming there - to keep the temperature increase to no more
than two degrees. Recognition of the need to confine the temperature
rise to this point was almost the only element of agreement at the oth-
erwise dismal United Nations climate-change summit in Copenhagen in
December 2009. The pressing issue of how to achieve this, however, was
not something that the 190 countries were able to agree there.
To keep within range of the two-degree limitation target, the general
scientific consensus is that GHG levels ought to be stabilized at 450-
550ppm of CO
2
e. The major review of the economics of climate change,
led by UK economist Sir Nicholas Stern (see p.41), took as its starting
Professor James Hansen: one of several scientists
who have criticized the IPCC's reports for not taking
sufficient account of the extent to which climate
change precipitates further climate change.
