Pete Clarke Wrote:
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> But correlation is evidence of causation when
> there is a testable mechanism involved.
>
> Go back to the birds. The correlation exists but
> is meaningless because there is no connection
> between the two events.

Exactly, and that is what the fallacy that Anthony is trying to invoke here says: you cannot prove causation from a correlation. (implied: a correlation alone). As in the examples given there may be no connection between the two events, i.e., the NFL wins the superbowl and the stock market goes up. There is statistical evidence that shows a fairly high positive correlation between these two; however, in the years the "superbowl effect" was popular, the NFL tended to win more often and the market tended to be up more years rather than down. There is no connection, no causation, no superbowl effect.

> However, if, for example,
> we discovered that birds were attracted to green
> grass, and the greener the grass the more likely
> it is that birds will be nearby, we have a
> physical, testable mechanism - correlation becomes
> evidence of causation (green grass causes there to
> be more birds) and evidence against causation
> (birds make grass green).

The birds are certainly attracted to growing grass; they eat grass seeds and they eat insects that eat growing grasses. So the grass could "cause" the birds to appear. In addition, since some seeds are excreted by the birds along with fresh fertilizer in the form of droppings, the birds could potentially cause more grass to grow. But both grass and birds are "caused" to appear in the spring because it's spring...the earth's movement is the ultimate cause.

> The analogies fail because the link between global
> warming and man-made greenhouse gasses is not
> simply one of correlation. There is also the
> knowledge that those gasses, when formed
> "naturally", act as greenhouse gasses. It is a
> known physical process. The only real argument is
> whether man made gasses are having a significant
> effect on an already-existing warming trend and
> how the word "significant" is interpreted. There
> is no doubt that CO2, whether from animal
> respiration, volcanoes or power stations, has a
> warming effect. This is based on the physical
> properties of the gas in the atmosphere, not on
> correlations.

It is not the analogy that fails here. My analogy is meant simply to illustrates the fallacy. Anthony's analogy did not do that. I believe what you mean to say here is that the fallacy invoked by Anthony, that fallacy itself, fails here.

> The only real unknown is whether the 2% (or
> whatever) of CO2 added by humanity to the
> atmosphere has a negligible effect or is putting
> enough energy into the atmosphere to disrupt
> climate patterns (which is the real issue, not a
> couple of degrees mean global temperature
> increase). To claim that it is just a correlation
> is to ignore the physics.

I have not claimed any such thing, so I'll leave you to work things out with Anthony.