Backcasting of Climate Models
http://www.applet-magic.com/backcastingpod.htm
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Thayer Watkins
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& Tornado Alley
USA
The Backcasting of Climate Models
Meteorological weather forecasting models are tested and refined on the
basis of the stringent criterion of the usefulness of their forecasts. As a
result weatherforecasting models are of high quality and meteorology is a
hard science, as least as hard of a science as the subject matter allows.
Weather systems are subject to near infinite sensitivity to initial
conditions so it is physically impossible to make useful weather forecasts
beyond a week or so.
Climate models are not generally subjected to as stringent criteria of
validity as weather models. By an act of faith the model builders run
them to obtain projections decades, even centuries, into the future. It is
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felt that the climate models cannot be tested because it would take too
long to wait for a verification of their projections. Their projections are
not even in principle forecasts because the modelers have no way of
knowing what exogenous events such as major volcanic eruptions might
occur.
The Intergovernmental Panel on Climate Change (IPCC) considers
validation of its 15 climate models to consist of reproducing the current
climate characteristics. The models do alright on some climate
characteristics such as the latitudinal profile of zonal temperature means
but fail miserably on the climate characteristic of cloudiness. For more
on these validity tests see IPCC model validation.
The IPCC does not consider the more appropriate validation criterion of
projection the recent rates of increase of climate characteristics. For an
analysis of how well the climate models do at computing the rate of
change of temperature by latitude for the period from 1970 to 2001 see
Polar versus Equatorial Warming. The results show that the climate
models have some success in explaining the qualitative characterics of
the data but they also have failures in the quantitative characteristics.
On a quantitative level the errors are so large as to make the projections
over a century period useless. The errors in the projection models are
cumulative so that if there is 200 percent error over a thirty year period
the error over a hundred year period will on the order of 600 percent.
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However it is not true that the accuracy of the climate models cannot be
tested without waiting 50 years or so. The climate models can be run
backwards just as well as forward. Instead of a forecast they would give a
backcast of the climate characteristics of the past. Patrick J. Michaels in
his book, Meltdown, gives the backcasting of two climate models from
about 1993 back to 1905. One is the first Coupled Global Climate
Model(CGCM1) from the Canadian Centre for Climate Modeling and
Analysis and the other is British, the second Hadley Centre for Climate
Prediction and Research. The data were scaled from the Michaels' graph.
Here is the comparison of the backcasts of global temperature from the
Canadian model in comparison with the observations.
Although the model gets the shape generally right the timing is off and
that shape had to have come from inputting the sulfate aerosol estimates
which may not have been independent estimates but values chosen on the
basis of the known observations of global temperature. Nevertheless the
backcast change in temperature was 96 percent higher than the
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observational change of the eighty eight year period. That is nearly a 100
percent error per century.
There is an anomaly in the graph. The CGCM1 should start at the same
level at the end of the period as the observations. If the CGCM1 figures
are shifted down to coincide with the 1993 observations here is what the
graph looks like.
The performance of the CGCM1 climate model looks even less
impressive in this corrected version. This shift however does not alter the
performance of the model in terms of the errors in computing the
temperature changes. Generally the CGCM1 drastically overestimates
the temperature change. On the basis of this performance it is clear that
the CGCM1 can be tossed out. One of the exasperating aspects of the
IPCC, and there are many, is that it pretends that climatology is a hard
science but it, the IPCC, cannot differentiate among 15 different climate
models as to which ones are best.
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Now for the British model.
The general shape of the model value line is "sort of" the same as the
observation line, but it misses the global warming which occurred from
about 1915 to about 1938 and the global cooling from 1940 to 1960. In
terms of the temperature change over the entire period the model is
pretty good, being only 12 percent too small. However looking at the
graph the two curves cross at six points and it appears to be just a
coincidence that one of the crossings was close to the end of the
backcasting interval. At about 1955 the error would have been about 200
percent. This indicates that the measure of performance should be some
average error over the backcasting period. However clearly the Hadley
Centre model is superior the model of the Canadian Centre for Climate
Modeling and Analysis. However it is not certain whether even the
Hadley Centre model is sufficiently accurate to have any relevance in
economic policy decisions. In particular, it does not seem accurate
enough to be the basis for the developed countries imposing a trillion
dollar a year cost to their economies. And that trillion dollar a year cost
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may end up being a trillion dollar a year transfer to the governments of
developing countries for the purchase of their carbon emissions quotas.
The global temperature change over the past century has been about
0.7°C, some of which has been due to increases in solar intensity. No
climatic disasters have occurred as a result of that temperature change.
The projected increase in global temperatures over the next century is on
the order of 1.2°C. There is no basis for climatic difficulties stemming
from that increase other than from non-validated and invalidated
computer climate models. That is not to say there will not be serious
weather. There will be serious weather problems just as there will be
earthquakes and tsunamis, but no amount of government regulation will
change that. It used to be that tribal leaders; i.e., governments; would
throw a few virgins into the volcanoes to placate the gods and prevent
eruptions. Now governments in developed countries want to throw their
economies into the cauldron in repentence for their prosperity. It all
stems from some cultural notion that if one makes a sacrifice then surely
one will get something in return. For millenia religions have been
organizing sacrifices to placate the gods and everyone of those sacrifices
has been a complete and total waste. The names have changed by the
game is the same.
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