There is considerable debate over the fidelity and utility of global climate models
(GCMs). This debate occurs within the community of climate scientists, who disagree
about the amount of weight to give to climate models relative to observational analyses.
GCM outputs are also used by economists, regulatory agencies and policy makers,
so GCMs have received considerable scrutiny from a broader community of scientists,
engineers, software experts, and philosophers of science. This report attempts
to describe the debate surrounding GCMs to an educated but nontechnical audience.
Key summary points
- GCMs have not been subject to the rigorous verification and validation that is
the norm for engineering and regulatory science.
- There are valid concerns about a fundamental lack of predictability in the complex
nonlinear climate system.
- There are numerous arguments supporting the conclusion that climate models
are not fit for the purpose of identifying with high confidence the proportion
of the 20th century warming that was human-caused as opposed to natural.
- There is growing evidence that climate models predict too much warming from
increased atmospheric carbon dioxide.
- The climate model simulation results for the 21st century reported by the Intergovernmental
Panel on Climate Change (IPCC) do not include key elements
of climate variability, and hence are not useful as projections for how the 21st
century climate will actually evolve.
Climate models are useful tools for conducting scientific research to understand the
climate system. However, the above points support the conclusion that current GCMs
are not fit for the purpose of attributing the causes of 20th century warming or for
predicting global or regional climate change on timescales of decades to centuries,
with any high level of confidence. By extension, GCMs are not fit for the purpose of
justifying political policies to fundamentally alter world social, economic and energy
systems. It is this application of climate model results that fuels the vociferousness of
the debate surrounding climate models.
Judith Curry –Â Global Warming Policy Foundation – 2017