Hypothesis 1: Human influence on climate
variability and change is of minimal
importance, and natural causes dominate
climate variations and changes on all time
scales. In coming decades, the human influence
will continue to be minimal.
Hypothesis 2a: Although the natural
causes of climate variations and changes
are undoubtedly important, the human influences
are significant and involve a diverse
range of first- order climate forcings, including,
but not limited to, the human input of
carbon dioxide (CO2). Most, if not all, of
these human infl uences on regional and
global climate will continue to be of concern
during the coming decades.
Hypothesis 2b: Although the natural
causes of climate variations and changes are
undoubtedly important, the human influences
are significant and are dominated by the emissions
into the atmosphere of greenhouse
gases, the most important of which is CO2. The
adverse impact of these gases on regional and
global climate constitutes the primary climate
issue for the coming decades.
These hypotheses are mutually exclusive.The skeptical position is the first, the IPCC is 2b. The paper makes the case for 2a saying that it is best supported by the available evidence.
Thus, the accumulated evidence can only
provide support for one of these hypotheses.
The question is which one?
Unfortunately, the 2007 IntergovernmentalInstead, argues the paper, a borader analysis of factors is needed, which includes the regional level:
Panel on Climate Change (IPCC)
assessment did not sufficiently acknowledge
the importance of these other human climate
forcings in altering regional and global
climate and their effects on predictability at
the regional scale. It also placed too much
emphasis on average global forcing from a
limited set of human climate forcings. Further,
it devised a mitigation strategy based
on global model predictions.
Because global climate models do notRead the paper in full here. It raises important questions, not only on how to position yourself in the debate, but also what is the right way forward. Should there be models with regional prediction? Should these be taking into account many more variables? If so, should this be done through the IPCC?
accurately simulate (or even include) several
of these other first-order human climate
forcings, policy makers must be made
aware of the inability of the current generation
of models to accurately forecast
regional climate risks to resources on multidecadal
time scales. For example, how
the water cycle responds to the diversity of
climate forcings at the regional level will
be important information to policy makers
seeking to mitigate risks to water resources.