The more severe the emission cuts to be made, the
more it will usually cost. There is wide agreement that
in 2050 global average costs for GHG mitigation to-
wards stabilization between 710 and 445ppm of CO
2
-
eq are between a 1 per cent gain and a 5.5 per cent
decrease in global GDP. This corresponds to slowing
average annual global GDP growth by less than 0.12
percentage points, a rate that is much smaller than
the annual fluctuation of GDP. GDP losses by 2030
are estimated at a cumulated 3 per cent since 2000
for the ambitious stabilization level of atmospheric
GHGs between 445 and 535 ppm CO
2
-eq. This corre-
sponds to the estimated annual growth rate. If these
predictions are correct, climate change mitigation
would slow down global economic growth by one
year by 2030.
For increases in global average temperature of less
than 1–3°C above 1980–1999 levels, some impacts
are projected to produce market benefits in some
places and sectors while, at the same time, imposing
costs in others. Global mean losses from impacts of
climate change could be 1–5 per cent of GDP for 4°C
of warming, but regional losses could be substantially
higher. The social cost of carbon dioxide is the price
of damages from climate change aggregated world-
wide. This cost was estimated at 12 USD per tonne of
CO
2
for 2005 and it is projected to increase over time.
As these estimates do not include non-quantifiable
impacts, they might underestimate real net costs.
Weighing the costs of mitigation against its benefits
(that is, against the avoided impacts) does not as yet
allow us to determine a stabilization level where ben-
efits exceed costs.
Adaptation and mitigation 53
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