Environmental Engineering Reference
In-Depth Information
ents. It is becoming increasingly probable that the often-stated desire to restrict warming to
less than 2°C is not going to be achieved.
To put the significance of this into context, a global mean temperature decrease of
about 3.5 to 5.0°C is all that separates us from the last glaciation and we will be moving in-
to territory that has not been encountered during the evolution of the world's civilizations.
The uncertainties that show up as the ranges of projected temperature increase are not
just a product of us being unable to guess how the world's energy-driven economies will
develop over the next 100 years. For example, another important element of uncertainty
is the behaviour of the various positive and negative feedback mechanisms that influence
Earth's radiation budget and their resulting potential impact on climate sensitivity (roughly
how much the climate will change for a doubling of carbon dioxide concentration).
Theprojectedwarmingisalsonotgloballyuniform.Itwillcontinuetobemostintense
in the Arctic. Under the more moderate B1 SRES scenario, half the Arctic summer sea ice
would be lost by 2100. However, we appear on track to probably having a summer ice-free
Arctic Ocean by or before 2050.
One practical point needs heavy emphasis: If our governments have any true aspira-
tion to restrict global warming to a level that is below 2°C, you will already have noticed
that it will not suffice to simply stabilize emissions. Total emissions must be very con-
siderably reduced to the point where atmospheric concentrations substantially decline in
the first part of this century. This will not be easy, but we no longer have time to rely on
the actions of others in the future. When politicians congratulate themselves that national
emissions have plateaued, even though gross domestic product has risen, you know this is
exactly what they are doing: relying with the faith of Micawber that someone somewhere
will come up with an easy solution. Meanwhile, our children and grandchildren are looking
towards a future that is very different from that which was bequeathed to us by our fore-
bears. Past and future anthropogenic carbon dioxide emissions will continue to contribute
to warming, sea level rise and acidifying oceans for more than a millennium even if emis-
sions could be immediately stabilized today.
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