I thought it might be worthwhile to put forward some other opinions on the issues raised.
Solar luminosity:
'There are observed changes in solar luminosity which account for something like 0.12[-0.4 to 00.0] watts per meter squared which is small compared to the 2.3 watts per meter squared estimated for Greenhouse gases. These changes are related to changes in sunspot activity, solar diameter, umbral penumbral ratio.
Nonetheless there are many statistical studies which suggest a correlation with temperature and other weather parameters that is far stronger than the measured changes in luminosity imply. Is this just statistics fooling us or is there some unknown amplifier?
Some studies find that these parameters correlate with cloud cover which would provide such an amplifier. But convincing physical arguments have not been made.'[1]
Weather versus climate:
'[Roger Pielke Sr]...I often hear scientists say “weather is unpredictable, but climate you can predict because it is the average weather”. How can they prove such a statement?
They claim it’s a boundary force problem since they look at it from an atmospheric perspective. They are assuming that the land surface doesn’t change much, the ocean doesn’t change much and that the atmosphere will come in some kind of statistical equilibrium. But the problem is the ocean is not static, the land surface is not static.
In fact I recently posted a blog on a paper by Filippo Giorgi... What he is doing is a transition in thinking. He concludes there are components of a boundary problem and components of an initial value problem with respect to 30 year predictions. If it’s a combination of the two, it therefore is an initial value problem and therefore has to be treated just like weather prediction!
[interviewer] What’s the difference between a boundary value and initial value problem?
[Roger Pielke Sr] Initial value means it matters what you start your model with, what your temperature is in the atmosphere, temperature in ocean, how vegetation is distributed, etc. They say it doesn’t matter what this initial distribution is; the results will equilibrate after some time, the averages will become the same.
The problem is that the boundaries also change with time. These are not real boundaries; these are interfaces between the atmosphere and ocean, atmosphere and land, and land and ocean. These are all interactive and coupled.
There are two definitions of climate: 1) long term weather statistics or 2) climate is made up of the ocean, land ice sheets and the atmosphere. The latter definition is adopted by a 2005 NRC report on radiative climate forcings (see). This second definition indicates that it depends what you start your model with, e.g. if you start in the year 1950 with a different ocean distribution, you will get different weather statistics 50 years from then.
The question is why should we expect the climate system to behave in such a linear well behaved fashion when we know weather doesn’t? In the Rial et al. paper (see), we show from the observations that, on a variety of time scales, climate has these jumps, these transitions, and these are not predicted by models. These are clearly non-linear and are clearly related to what you start your climate system with.
Most climate scientists, if you present this information to them, agree that climate is an initial value problem. There are some that still argue it’s a boundary problem. That makes it easier for them to say “if we put in CO2 from anthropogenic activities you get this very well behaved response for the next 100 years”. However, this perspective is not supported at all by the observational record. What that means is that when we perturb the climate system we could be pushing ourselves towards or away from threshold changes we don’t understand. There is a risk in perturbing the climate system, certainly, but I don’t think we can predict it.'[2]
The precautionary principle:
'Q272 Lord Lawson of Blaby: ...Another thing in the [UK Government] White Paper which the government subscribed to was the precautionary principle. All of us in our daily lives take precautions but how do you interpret this in practical terms? How useful is it in terms of deciding which of the number of policy options to take?
Dr Helm: It is like sustainability and sustainable development. They sound very good in practice but one has to work out what exactly people mean when they are applied in particular circumstances. What do you want to be precautionary about? Do you want to be precautionary about the costs and changing current behaviour, reducing people's current standard of living in order to achieve a possible outcome, or do you want to be precautionary about how much climate change you get, even if that means higher costs to individuals? That is not normally specified. You can make just as good an argument about being precautionary on the cost side as you can about being precautionary on the climate change side. Normally, what people mean by this is some form of risk aversion. You can only be risk averse about things over which you have probabilities about. If you are genuinely uncertain, you do not have a probability as to what the outcomes are going to be. It does not mandate any particular action whatsoever. The final thing to say on the precautionary principle is there tends to be an important sub-part of this which relates to the question of things that are irreversible. This is important in the climate change debate and in the environment debate more generally. If, for example, a policy is quite likely to lead to the extinction of species, this is in any reasonable time irreversible. Therefore, we should put special weight and concern to things that are going to have that kind of effect. In the climate change area, in one sense, it is pretty obvious that the process of climate warming is irreversible in any reasonable human time span. Whether the consequences are irreversible is less obvious. I do not claim to understand the science, long distance, of how these effects play out, but that point illustrates the general one that one should be very precautionary about how one uses the precautionary principle. One should not think that it mandates a particular outcome which says we must do a great deal about this problem now.'[3]
[1] 'Global Climate Change: A Skeptic’s Perspective', Prof. William R. Cotton of the Department of Atmospheric Science, Colorado State University.
http://climatesci.colorado.edu/wp-content/uploads/2007/05/cotton-climate.pdf
[2] Roger A. Pielke Sr, Emeritus Professor of the Department of Atmospheric Science, Colorado State University. Interview by Marcel Crok, January 2007.
http://climatesci.colorado.edu/2007/04/30/interview-by-marcel-crok-of-roger-a-pielke-sr-jan-2007/
[3] Prof. Dieter Helm, Official Fellow in Economics, New College, Oxford. Evidence to the UK House of Lords Economic Affairs Select Committee.
http://www.publications.parliament.uk/pa/ld200506/ldselect/ldeconaf/12/5022206.htm