Re: [asa] Level of certainty in science

From: PvM <>
Date: Thu Feb 08 2007 - 15:06:57 EST

Definition of climate (Edward Lorenz):
"Climate is what you expect, weather is what you get."

Updated for the 21st century (Myles Allen):
"Climate is what you affect, weather is what gets you."

Some relevant papers and there are many many relevant papers on this
and related topics available on the internet:

Realclimate commentary and fair warnings

and an overview of climate sensitivity issues

The IPCC says that climate sensitivity is likely to be in the range of
1.5-4.5C, an estimate which has not changed for many years. Originally
this was based on very limited evidence, but subsequent research
appears to confirm that this early estimate was a pretty good (if
lucky) one. However, there is still a 3 degree difference between the
high and low ends of this range (which are themselves not hard
limits), and moreover the use of a "likely range" is a rather woolly
description of the uncertainty. So it would be nice to have a better

And the AR4 draft chapters
contain much relevant information on this topic

On NERC a discussion between sceptics and NERC scientists provides
some powerful insights

<quote>Perhaps we can go back to thinking about climate science
itself. The issue is the cause of the recent warming and the prospects
for the near future. The greenhouse effect is the basic mechanism that
links the human input of greenhouse gases and the warming of the
planet. If this warming effect from these added gases is somehow not
operating, what is the reason? And if not what does explain the
observed warming when all the natural factors driving climate have
hardly changed over the last 40 years?</quote>

The Dutch KNMI (Royal Weather Institute) has excellent data and model
results which can be compared with actual data.

And the stern Review on the Economics of Climate Change

On 2/8/07, PvM <> wrote:
> These are excellent points and I believe many of your concerns can be
> addressed by the following realization
> 1. These models are based on well known laws of physics to model the
> circulation as well as the thermodynamics
> 2. These models may miss relevant processes, such as in the past aerosols
> Models have been used for hindcasts, and the suggestion that such
> hindcasts can be made to fit by 'endless fiddling' misses the point
> that there is not that much to fiddle with.
> A good example of the relevance of models was when models were run
> including natural forcings only versus natural and anthropogenic only
> when running with both did the models show a close match with the
> actual observations.
> Now predictions over time mean that uncertainties will grow, which
> helps understand why the range of predictions grows significantly. By
> running a multitude of models with a multitude of scenarios,
> scientists can test these scenarios. One of the larger unknowns in the
> future is the amount of forcings.
> These models are based on the same models used for predictions of the
> weather, although climate models, because of their coarse modeling
> grids, are often unable to accurately resolve climate details for
> small regions.
> To understand the effort on both hindcast as well as forecast, it may
> be helpful to read the AR4 draft or the TAR chapters which address
> these issues. Much effort is spent on model validation as so much
> depends on their accuracies.
> On 2/7/07, Don Winterstein <> wrote:
> >
> > On the face of it one of the more disturbing things about trust in climate
> > scientists' predictions is their record or lack thereof on forecasts. We
> > know how to do hindcasts, and after fiddling endlessly with them they can
> > look impressive. But forecasts--if accurate--are where the payoff will be.
> > How good are climate scientists at forecasting anything? To my knowledge
> > they have no record.
> >
> > If so, by taking the forecast capabilities of their models seriously we'd be
> > sticking our necks out for people who have essentially no record of either
> > success or failure. That would make me nervous if I were betting a lot on
> > their being correct.
> >
> > Don
> >
> >
> >
> > ----- Original Message -----
> > From: PvM
> > To: Don Winterstein
> > Cc: asa
> > Sent: Tuesday, February 06, 2007 8:48 PM
> > Subject: Re: [asa] Level of certainty in science
> >
> > You are correct that skepticism about models is good. However, models
> > do not exist in a vacuum but rather take existing data from the past
> > and use hindcasts as well as forecasts to validate the performance. In
> > addition, climate models are based on laws of physics and while they
> > may miss relevant processes, climate models are well founded in
> > science.
> > Sure, all these models may be wrong and the earth may end up cooling
> > and the scientists may look foolish, on the other hand the earth may
> > actually follow the predictions and who would look foolish then?
> > Science is never certain and global warming is no exception but there
> > are good or even strong reasons to believe that these predictions are
> > quite valid.
> >
> > <quote>For example, the Program for Climate Model Diagnosis and
> > Intercomparison at Lawrence Livermore National Laboratory has been
> > conducting model comparison and validation tests since 1989 (including
> > the climate models used by the IPCC), and published a publicly
> > available report of its research in the summer of 2004. [see
> > ]</quote>
> >
> > IPCC is also involved in validation of models and I believe that most
> > scientists understand that models are supplementary to other
> > scientific data and cannot stand alone.
> >
> >
> >
> > AR4 draft also shows the hard work done here:
> >
> > * Executive Summary
> > * Advances in Modeling
> > * Evaluation of Contemporary Climate as Simulated by Coupled Global
> > Models
> > * Evaluation of Large Scale Climate Variability as Simulated by
> > Coupled Global Models
> > * Evaluation of the Key Relevant Processes as Simulated by Coupled
> > Global Models
> > * Model Simulations of Extremes
> > * Climate Sensitivity
> > * Evaluation of Model Simulations of Thresholds and Abrupt Events
> > * Representing the Global System With Simpler Models
> >
> > <quote>There is considerable confidence that climate models provide
> > plausible quantitative estimates of future climate change,
> > particularly at continental scales and above. Confidence in these
> > estimates is higher for some climate variables (e.g. temperature)
> > than for others (e.g. precipitation). This confidence comes from the
> > foundation of the models in accepted physical principles and from
> > their ability to reproduce observed features of recent climate (see
> > Chapters 8, 9) and past climate changes (see Chapter 6). In this
> > summary we highlight areas of progress since the TAR:
> > </quote>
> >
> >
> >
> >
> > On 2/6/07, Don Winterstein <> wrote:
> > >
> > >
> > >
> > > Pim Van Meurs wrote: "What is so scary about science being correct once
> > > again? If one
> > > believes this to be scary, imagine how scary it could be when
> > > Christians, as Augustine pointed out, are observed spouting scientific
> > > nonsense?"
> > >
> > > Who's got more to lose here? The climate data may be fairly firm, but the
> > > models, from which scientists make predictions, are likely much less
> > > trustworthy. They're Earth science models, after all. If Earth starts
> > > cooling within a few decades--as it's been known to do, climate scientists
> > > and other scientists by association will lose credibility for a long time
> > to
> > > come.
> >

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Received on Thu Feb 8 15:08:29 2007

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