[ExI] Forecasting experts’ simple model leaves expensive climate models cold

[Alfio Puglisi]

On Fri, Dec 11, 2009 at 6:58 PM, Max More <max at maxmore.com> wrote:

> Another interesting piece from Armstrong and Green:
>
> Forecasting experts’ simple model leaves expensive climate models cold
>
> A simple model was found to be produce forecasts that are over seven times
> more accurate than forecasts from the procedures used by the United Nations
> Intergovernmental Panel on Climate Change (IPCC).
>


> This important finding is reported in an article titled “Validity of
> climate change forecasting for public policy decision making” (
> http://kestencgreen.com/gas-2009-validity.pdf) in the latest issue of the
> International Journal of Forecasting. It is the result of a collaboration
> among forecasters J. Scott Armstrong of the Wharton School, Kesten C. Green
> of Monish University, and climate scientist Willie Soon of the
> Harvard-Smithsonian Center for Astrophysics.
>

I don't understand this paper. They first develop a simple "temperature
constant" model and compare it with observations. Well, they show right in
the second graph, and also in the text, that their model has an average
error of 0.4C when "forecasting" from 1850 to a time horizon of one hundred
years, and, surprise, the error grows larger with the time horizon. That
means that a temperature trend is at work. Eyeballing the GISS temperature
graph, I derived an observed rate of 0.6 degrees from 1900 to 2000, so it's
in the ballpark. The observed warming is thus compatible with the error in
their model at the right timescales. In other words, temperature is not
constant.

They go on comparing an hypothetical IPCC-like prediction (linear warming of
0.03C/year) from 1850 on, but changing the metric (which is sufficiently
obscure that I didn't understand in the few minutes I dedicated to the
subject). They find little agreement between prediction and observations,
conveniently forgetting that IPCC predictions are for the next century, when
CO2 forcing will be substantially higher than in the 1800s.

And look at their conclusion:

"The benchmark forecast is that the global mean temperature for each year
for the rest of this century will be within 0.5 ◦ C of the 2008 figure."

I could say so just looking at the GISTEMP graph and extrapolating a line
for the next century! And this is already a more complex model then their,
which is a flat line from 2008 on. What they show is simply that last
century worth's of global warming was on the order of 0.5C. Well, we already
know that. So I don't understand what they are trying to demonstrate.

Alfio
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