Abstract
The sensitivity of the climate system to increasing CO2 concentration and the
response at decadal time scales are still major factors of uncertainty for the
assessment of the long and short term effects of anthropogenic climate change.
Here we demonstrate that it is possible to use Ruelle's response theory to
predict the impact of an arbitrary CO2 forcing scenario on the global surface
temperature of a general circulation model. Response theory puts the concept of
climate sensitivity on firm theoretical grounds, and addresses rigorously the
problem of predictability at different time scales. Conceptually, our results
show that climate change assessment is a well defined problem from a physical
and mathematical point of view. Practically, our results show that considering
one single CO2 forcing scenario is enough to construct operators able to
predict the response of climatic observables to any other CO2 forcing scenario,
without the need to perform additional numerical simulations, thus paving the
way for redesigning climate change experiments from a radically new
perspective.
