As near as I can tell from his writing, his key objection is the inaccuracy of climate models and their predictive failure. While it's a truism that any model with enough free variables can "fit" a data set, this does not render the exercise useless.
Nor are models the only reason we think people are driving the global temperature change. There are still large numbers of plausible biological/chemical explanations for man-made global warming, and fewer that involve random fluctuations.
In the end, though, I think the best argument is simply caution. There's no backup planet if people like you are wrong, so it's best to proceed as if we're tiptoeing on the edge of a cliff. If 99% of scientists are wrong, then all we'll have wasted are funding dollars as effort. If you're wrong, we might see the coasts become uninhabitable, and wars break out over things like water and land.
Nor are models the only reason we think people are driving the global temperature change. There are still large numbers of plausible biological/chemical explanations for man-made global warming, and fewer that involve random fluctuations.
In the end, though, I think the best argument is simply caution. There's no backup planet if people like you are wrong, so it's best to proceed as if we're tiptoeing on the edge of a cliff. If 99% of scientists are wrong, then all we'll have wasted are funding dollars as effort. If you're wrong, we might see the coasts become uninhabitable, and wars break out over things like water and land.