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Flawed Climate Models

A Skeptical View of Climate Models
By Hendrik Tennekes


A Skeptical View of Climate Models
By Hendrik Tennekes, retired Director of Research, Royal Netherlands
Meteorological Institute,

Here in the Netherlands, many people have ranked me as a climate
skeptic. It did not help much that I called myself a protestant
recently. I protest against overwhelming pressure to adhere to the
climate change dogma promoted by the adherents of IPCC. I was brought
up in a fundamentalist protestant environment, and have become very
sensitive to everything that smells like an orthodox belief system.
The advantages of accepting a dogma or paradigm are only too clear.
One no longer has to query the foundations of one's convictions, one
enjoys the many advantages of belonging to a group that enjoys
political power, one can participate in the benefits that the group
provides, and one can delegate questions of responsibility and
accountability to the leadership. In brief, the moment one accepts a
dogma, one stops being an independent scientist.


A skeptic, on the other hand, accepts both the burdens and the
pleasures of standing on his own feet. One of the disadvantages a
skeptic has to cope with is the problem of finding adequate research
support. The other side of that coin is that an independent scientist
has a great opportunity to think better and delve deeper than most of
his or her colleagues. Let me take an example in which I have been
involved for thirty years, the problem of a finite prediction horizon
for complex deterministic systems. This, the very problem first
defined by Edward Lorenz, still is not properly accounted for by the
majority of climate scientists. In a meeting at ECMWF in 1986, I gave
a speech entitled "No Forecast Is Complete Without A Forecast of
Forecast Skill." This slogan gave impetus to the now common procedure
of Ensemble Forecasting, which in fact is a poor man's version of
producing a guess at the probability density function of a
deterministic forecast. The ever-expanding powers of supercomputers
permit such simplistic research strategies.


Since then, ensemble forecasting and multi-model forecasting have
become common in climate research, too. But fundamental questions
concerning the prediction horizon are being avoided like the plague.
There exists no sound theoretical framework for climate predictability
studies. As a turbulence specialist, I am aware that such a framework
would require the development of a statistical-dynamic theory of the
general circulation, a theory that deals with eddy fluxes and the
like. But the very thought is anathema to the mainstream of dynamical
meteorology.


Climate models are quasi-deterministic and have to simulate daily
circulation patterns for tens of years on end before average values
can be found. The much more challenging problem of producing a theory
of climate forecast skill is left by the wayside. In IPCC-documents
one finds phrases like "climate surprises", showing that the
IPCC-staff is unaware of the ignorance it reveals by that choice of
words, or unwilling to state forcefully that climate predictability
research deserves much more attention than it has received so far.


This is no minor matter. A few years after launching my slogan on
forecast skill I chanced upon a copy of Karl Popper's "Open Universe"
and discovered that Popper had anticipated the problems caused by the
Lorenz paradigm. His claim that scientists should be held accountable
for the accuracy of their predictions boils down to the requirement
that they have to compute in advance the reliability of their
computations. For complex models, Popper wrote, this demand leads to
"infinite regress": computations of forecast skill are much harder
than the forecasts themselves, and the next level, forecasting the
skill of the skill forecast, is insurmountable when a complex system
such as the climate is involved. Popper concluded that the positivist
claims of science are in general unwarranted. In 1992 I wrote an essay
for Weather to explain the issue in detail.


Climate skeptics also face a sociological problem. They agree only in
their protest against the prevailing dogma. Some base their protest on
various versions of the neoconservative paradigm. Bjorn Lomborg, for
example, ignores the many efforts of the environmental movement that
have contributed to improving conditions in the industrialized world.
Speaking scientifically, I submit he has overlooked a crucial social
feedback mechanism. Other skeptics use other paradigms. Roger Pielke
Jr. bases his work on the vulnerability paradigm, a choice very
appealing to me. Lots of outsiders in the climate business employ a
supremacy of physics paradigm, attacking one or more of the physical
details of the climate problem, and hoping that they can prevail by
proving the climate orthodoxy wrong.


In my view, their conceptual mistake is that the physics of complex
systems does not provide opportunities for settling the climate debate
that way. In 1987, I gave a speech in London entitled "Illusions of
Security, Tales of Imperfection". I dealt with the shortcomings of
numerical weather forecasting there, but similar arguments apply to
climate forecasting. The climate orthodoxy perpetrates the
misconceptions involved by speaking, as IPCC does, about the
Scientific Basis of Climate Change. Since then, I have responded to
that ideology by stating that there is no chance at all that the
physical sciences can produce a universally accepted scientific basis
for policy measures concerning climate change. In my column in the
magazine Weather in February of 1990, I wrote:
"The constraints imposed by the planetary ecosystem require continuous
adjustment and permanent adaptation. Predictive skills are of
secondary importance."


Today I still feel that way. I cannot bring myself to accept any type
of prediction paradigm, and choose a adaptation paradigm instead. This
brings me in the vicinity of Roger Pielke Sr.'s emphasis on land-use
changes and Ronald Brunner's modest bottom-up alternatives. It goes
without saying that I abhor such dogmas as various claims to Manage
The Planet or Greenpeace's belief in Saving the Earth. These
ideologies presuppose that the intelligence of Homo sapiens is capable
of such feats. However, I know of no evidence to support such claims.


Back to Lorenz. Complex deterministic systems suffer not only from
sensitive dependence on initial conditions but also from possible
sensitive dependence on the differences between Nature and the models
employed in representing it. The apparent linear response of the
current generation of climate models to radiative forcing is likely
caused by inadvertent shortcomings in the parameterization schemes
employed. Karl Popper wrote (see my essay on his views):
"The method of science depends on our attempts to describe the world
with simple models. Theories that are complex may become untestable,
even if they happen to be true.
Science may be described as the art of systematic oversimplification,
the art of discerning what we may with advantage omit."


If Popper had known of the predictability problems caused by the
Lorenz paradigm, he could easily have expanded on this statement. He
might have added that simple models are unlikely to represent
adequately the nonlinear details of the response of the system, and
are therefore unlikely to show a realistic response to threshold
crossings hidden in its microstructure. Popper knew, of course, that
complex models (such as General Circulation Models) face another
dilemma.


I quote him again: "The question arises: how good does the model have
to be in order to allow us to calculate the approximation required by
accountability? (…) The complexity of the system can be assessed only
if an approximate model is at hand."

From this perspective, those that advocate the idea that the response
of the real climate to radiative forcing is adequately represented in
climate models have an obligation to prove that they have not
overlooked a single nonlinear, possibly chaotic feedback mechanism
that Nature itself employs.


Popper would have been sympathetic. He repeatedly warns about the
dangers of "infinite regress." As a staunch defender of the Lorenz
paradigm, I add that the task of finding all nonlinear feedback
mechanisms in the microstructure of the radiation balance probably is
at least as daunting as the task of finding the proverbial needle in
the haystack. The blind adherence to the harebrained idea that climate
models can generate "realistic" simulations of climate is the
principal reason why I remain a climate skeptic. From my background in
turbulence I look forward with grim anticipation to the day that
climate models will run with a horizontal resolution of less than a
kilometer. The horrible predictability problems of turbulent flows
then will descend on climate science with a vengeance.

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