I think the argument can be illustrated in this way -

1. I smoke cigarettes
2. I suspect that cigarettes are likely to do me harm.
3. However, I feel I am as likely to suffer the same damage from passive smoking.
4. Therefore I don't need to stop smoking until everyone else stops.
5. Despite overwhelming evidence of smoking-related harm, I can always find somebody who can cast doubt on the official view.
6. Any illness I suffer may also be part of a "natural cycle" and co-incidental.
7. There are other environmental factors that could make me ill.

Therefore, why stop?

Phlogiston theory, vitalism, caloric theory of heat, miasma theory of infectious disease, Lamarck’s theory of inheritance of acquired characteristics and so on, all part of the history of science ("mhar" please note).

Yes climate like weather is not a constant. Some of the questions that this unbeliever worries about are as follows:

1. How much of the atmospheric CO2 is man made? How much is due to natural events such as volcanic activity?
2. What about other so called greenhouse gasses for instance water vapour? How are you going to control water vapour?
3. A physical chemist should be able to inform us in quantitative terms of the relative effectiveness of the variously named greenhouse atmospheric gases?
4. Another question for physical chemists is the heat trapping effect of the gases linear with concentration?
5. How about other effects such as solar radiation and solar activity (sun spots), the earths wobble about its axis; cosmic rays, and no doubt atmospheric scientists are aware of other confounding effects?
6. How important are negative feed back mechanisms such as the reflection of suns rays from clouds? Or the threatened golf stream block?
7. How important is statistical variation and unpredictability in a non linear climate system?

As for the various doomsday scenarios this is great material for Hollywood film makers etc. Is it really in the national interest to spend billions in preparation for speculative events? This could be a great waste of money? Surely there are more practical ways of using money?

The contrarian/sceptic argument seems to run something like this:

Global warming isn't happening........but even if it is -
It isn't a man made phenomenon........but even if it is -
We can't do anything about it..........but even if we can -
The Asia Pacific group is superior to Kyoto.

That's too many "buts" for this particular fella to take seriously.

To answer Anti-green's question about the relationship between increasing atmospheric carbon dioxide and increasing temperature.

The relationship is logarithmic, meaning that every additional increment of CO2 results in a lesser increment in temperature. Most of the temperature effect of increasing CO2 comes from the first incremental 50 ppm.

Assuming that the surface thermometer temperature record is accurate (and many scientists believe that, despite being corrected, the record may still include an urban heat island effect), then we had about a 0.6 deg. C increase in surface temperature in the 20th century.

Dick Lindzen, amongst others, has estimated that the increase in forcing from greenhouse gases over the same time period represents 2.7 W/m2 which is about 75% of the full 3.7 W/m2 that will be caused by doubling CO2 from pre-industrial levels.

In other words, as we proceed to full doubling we have about 0.2 deg. C of CO2-forced warming to go. Because that figure likely includes an urban heat island effect that is embedded in the "0.6 deg C warming" estimate, the real increase will be less than 0.2 deg, and trivial.

The only way that you can make further CO2 increases alarming is to adopt the IPCC technique of assuming that additional small increments of CO2 will causes a strong water vapour feedback loop.

As Lindzen concluded:

"what is known points to the conclusion that a doubling of CO2 would lead to about 0.5C warming or less, and a quadrupling (should it ever occur) to no more than about 1C. Neither would constitute a particular societal challenge. Nor would such (or even greater) warming likely be associated with discernibly more storminess, a greater range of extremes, etc."

Cathy

Hello anti-green. I'll give it a shot.
1. Around 24,000 million tonnes are man-made. Volcanic sources release approximatly 1% of what humans release (from wikipedia)

2. There are about 30 green-house gases in the atmosphere. After CO2, the next most important is methane (which is 60 times more potent than CO2, and has doubled in concentration in the last 200 hundred years, although lasts fewer years in the atmosphere). NO2 (laughing gas) is 270 times more potent than C02, and the concentration has increased by 20% since the industrial revolution. Water is difficult because high cloud traps heat, where as low cloud reflects it. (from the Wheather Makers).

3. In general (most potent to least): N02, methane, CO2, water
Longest lasting: CO2, NO2, methane, water

4. Thought to be logarithmic, but this does not factor in positive feed-back loops, such as the release of methane from peat bogs, melting of ice etc... This is currently subject to debate, and the exact parameters are still not known.

5. It is thought that solar activity may contribute to between 10%-30% of currently observed warming. However, in a literature review, Foukal et al. (2006), concluded that the variations in solar output were too small to have contributed appreciably to global warming since the mid-1970s. They also found that there was no evidence of a net increase in brightness during this period. More research is needed.

6. Very important. So important that they are generally included in most computer models. In particular, the gulf stream block is though to have been caused by a warming effect, which pushed Europe into an Ice Age (from the Weather Makers )

7. This question doesn't make alot of sense. Do you mean how important are statistical variations in climate reconstruction? Please rephrase.

" Is it really in the national interest to spend billions in preparation for speculative events?"
The days of spectulation are over. The time to act is now.

Sorry about the berevity. Best I can do given the word limit

I write to thank all who have taken the trouble to respond to my post with useful and pertinent information. For this I am most appreciative.

I understand that my question 7 on statistical variation is not clear. A good starting point would always be to quote 95% confidence intervals for estimates. A wide confidence interval would suggest a lack of precision in the estimate. However, a wide interval also has greater accuracy in the sense that the estimate is contained within the interval. By the same token a narrow interval has greater precision, but less accuracy. In other words there is a trade-off between accuracy and precision.

In a similar way in diagnostic testing there is a trade-off between a false negative and/or a false positive result. By altering the threshold of a test one can plot a “receiver operating curve.” That is the plot of true positive rate (sensitivity) against false positive rate (1-true negative rate or specificity).

For those that find this confusing I am reminded of a quip by professor Richard Dawkins. A type 3 represents the confusion between the definition of type 1 and type 2 errors