I haven’t said much about the global warming debate, as I’m not well read on natural sciences. Overall I’ve tended to think warming is real, partially man-made and a serious (but not catastrophic) problem.

This story made me think a bit though. A new report claims there’s a 90 percent chance (they call that “very high confidence”) that on balance, human activity since 1750 has made the Earth warmer.

First of all, the scientists are 90 percent humans cause warming to what degree? I don’t think anyone has said that natural fluctuations don’t affect climate at all. If emissions cause 1 percent of warming, that’s not that helpful for solving the problem. Even if you’re 100 percent certain.

To answer the question I read the report itself (OK, the policymaker summary, sue me). Soon after claiming a 90 percent chance that humans have caused more warming than cooling (page 3), the report claims that “most” of the warming is “very likely” (90-95 percent) to have been human-caused (page 8). Which is it — a 90 percent chance humans caused any warming, or most warming?

Two, it’s a natural tendency to wonder how much warming is man-made: If we messed it up, we should fix it. But in the end, why does it matter?

The pertinent questions should be, (A) is the Earth getting warmer, (B) is said warming harmful to human interests and (C) if yes and yes, can we do anything to stop it? If warming is man-made but harmless, there’s no reason to disrupt our lives. If it’s not man-made, but is harmful, we should do what we can to fix it.

(Of course, the causes of warming will matter in terms of how, exactly, to fix it. If our behavior is the problem, we need to stop that behavior; if it’s not, we need to do something else. But the debate right now is about how much to inconvenience ourselves for the sake of the climate. For that decision, the cause of warming is irrelevant.)

Finally, take a look at the chart on page 7 of the report, where the researchers look at various trends — whether they occurred, whether human activity caused them and whether they’ll continue in the future. Somehow, the first two columns have “likely” and “very likely” popping up a lot, but the future predictions have two “virtually certains.” In every single category, the scientists are equally or more certain about the future than the past.

Tell me how is it, exactly, that the panel is better at predicting the future than at analyzing established data? For example, it’s “very likely” that there were fewer and warmer cold days in the late 20th century, and “likely” human activity contributed to it, but “virtually certain” this will continue in the future.

One minor aside, from page 3 of the report:

“Anthropogenic contributions to aerosols (primarily sulphate, organic carbon, black carbon, nitrate and dust) together produce a cooling effect.”

Does that make it a good thing?

Robert VerBruggen blogs at http://www.therationale.com.