Geoscience Reference
In-Depth Information
What is dangerous climate change?
One of the most important questions for policy makers is what is dangerous climate
change? Of course, this does depend on where you live. For example, if you are in one of
the small island nations, any sea-level rise could be considered dangerous because it direc-
tly results in loss of land. However, looking at the bigger picture, if we are to cut global
GHG emissions we need a realistic target concerning the degree of climate change with
which we can cope. In February 2005, the British government convened an international
science meeting at Exeter, UK, to discuss this very topic. This was a very political science
meeting, as the UK government was looking for a recommendation to take to the G8 meet-
ing in Gleneagles. At that time Britain held both the chair of the G8 and presidency of the
EU, and the then prime minister Tony Blair wished to push forward internationally his joint
agenda of climate change reduction and poverty alleviation in Africa. The meeting did
come up with a 'magic number' of 2°C above pre-industrial average temperature: below
this threshold, there seem to be both winners and losers due to regional climate change, but
above this figure everyone seems to lose. It wasn't just this particular meeting that has
come up with the magic 2°C limit; many other researchers, including at the IPCC, have ar-
rived at similar conclusions from very different backgrounds and starting assumptions. But
it should always be remembered that this is a
political
number, as the definition of what is
dangerous climate change is a societal rather than scientific decision.
Figure 20
shows the
numbers of people that potentially could be at risk from water shortages, hunger, malaria,
and flooding by 2080. In
Figure 20
it seems 2°C is where the numbers increase radically,
particularly for water shortages, so 2°C has become a powerful and important symbol of
the challenges facing human society. The major problem is that it is unlikely we can keep
global temperature increases down to 2°C, as we have seen that temperature have already
increase by 0.8°C, and because of the inertia in the climate system by 2035 we already ex-
pect a rise of between 0.3°C and 0.7°C. So without doing anything, we will be up to
1.1‒1.5°C by 2035.
