Geoscience Reference
In-Depth Information
determinants of emissions growth and involve differing estimates about
economic growth, technology, and energy use in the coming years.
Can we pin down the sources of the differences more precisely? A
careful analysis fi nds that the biggest unknown arises from uncer-
tainty about future growth of the world economy: Will the world enjoy
robust economic growth like that from 1950 to 2005? Or will it stag-
nate, with slow technological change, recurrent fi nancial crises and
depressions, spreading pandemics, and occasional widespread wars?
These are the most important questions behind the divergent estimates
of CO
2
emissions.
The answers to these deep questions are at this point essentially
unknowable—like the roll of the wheel in the Climate Casino. No one
can reliably predict roulette wheels, the stock market, or future tech-
nologies. Remember that the recent deep recession was a complete sur-
prise for virtually every professional forecaster. Because of the deep
uncertainty about future economic growth, the divergence in emissions
projections shown in Figure 5 is unlikely to narrow signifi cantly in the
next few years.
People will naturally wonder how to respond to these vast uncer-
tainties when making climate-change policy. Isn't 100 years a long way
off? One reaction is to postpone action—to assume that because life is
uncertain, we should wait until we know more. Sometimes, if the stakes
are low and we will soon learn the right answer, waiting until the wheel
stops spinning is a reasonable approach.
But for climate change, waiting for the right answer is a perilous
course. It is like driving 100 miles an hour with your headlights off
on a foggy night and hoping there are no curves. We are unlikely to
resolve the uncertainties soon. Waiting for many years to act is costly
because of the delayed responsiveness of the economy and the climate
system to our actions. It is less costly to spread our investments over
time than to cram them all into a short time when the fog lifts and we
see disaster right in our path.
Economic research on dealing with uncertainties leads to the fol-
lowing conclusion: Start with a best-guess scenario for output, popula-
tion, emissions, and climate change. Take policies that will best deal
