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OT: Moorabal/Lal Lal wind farm 15-Jul-2009 At 10:30:19 AM R James

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anthonyk - thanks for a good sensible response.

If we look only at a cherry picked 100 years, there was an increase from 1910 to 1940, then flat until an almost identical increase from 1970 to 2000. The problem is that the increase from 1910 to 1940 was before all the fossil fuel activity started, therefore couldn't have been caused by anthropogenic CO2 - there wasn't a significant quantity. It therefore had to be natural causes. Why, then, would we assume that the second period of increase was caused by CO2, rather than the same cause as the first period?

Next, go to a longer period - say 4,000 years. We find that the recent temperature rise is very normal, as we come out of the "little ice age". Why, then are we trying to find something to blame? The CO2 hypothesis was a reasonable possibility, but it doesn't fit the data - no signature above the tropics, current cooling, evidence that CO2 lags temperature (and so it should - as the ocean warms, CO2 comes out of solution)

Even the greenhouse theory for increased CO2 doesn't fit. The effect of CO2 in the atmosphere is logarithmic. We've already seen most of the effect - doubling CO2 doesn't double the effect. It's like painting a window black, stopping all the light. Paint it again makes next to no difference.

Now to your point about what else could cause the increase? Perhaps the same circumstances that caused the 1910 - 1940 increase, and all the others in the past when it was hotter than now eg medieval warm period (800 - 1,000), Roman warm period (200 - 100BC) etc. We're coming out of the little ice age, and warming is expected.

You mention other effects (cosmic rays). Little is known about this. In fact preliminary tests have shown that cosmic rays do influence cloud formation, but the magnitude is not well understood (IPCC also state this). The European Organisation for Nuclear Research, supported by 9 countries, is setting up an experiment to test this. Unfortunately it's a couple of years from being ready. There's no doubt that cloud cover has a huge effect on the energy reaching us - just standing in the sun when a cloud comes over tells us this. Considering that we're talking about 0.6 - 0.7 degC over 160 years, it wouldn't take much change in cloud cover. Also, water vapour is the main greenhouse gas, and its concentration varies all over the place.

Throw in the Pacific Decadal Oscillation, sunspot activity, orbital changes, underwater active volcanos (,5,000 known). We just don't know enough all about these.

Then there's the problem of feedback. There's no question of increased CO2 causing direct significant temperature increase. The scientists agree the magnitude is small. What isn't agreed is whether we then experience negative or positive feedback. For example, higher temperature means melting of ice caps, therefore more heat absorbed. But it also means more cloud formation, and therefore more cooling, making it self regulating. We've never experienced thermal runaway in the past when CO2 and temperature has been higher, so why should we expect it now?

This is the problem with the IPCC models - they assume positive feedback will dominate, even though history tells us otherwise.

I'm not happy blindly accepting the CO2 hypothesis while all these questions are unanswered. If the models match some real data, I'd feel a lot more confident about the hypothesis. To me, it remains nothing more than an hypothesis, with little to support it.