A few weeks ago, I was perusing Grist when I ran across an ad for A Convenient Fiction, a slideshow rebuttal of Al Gore’s An Inconvenient Truth. The author was none other than Steve Hayward, who you might remember from the AEI-$10,000-payola scandal.

I had actually seen this slideshow discussed in the New York Times, and was interested to see it. In my previous communications with Hayward, he was at great pains to describe himself as someone who believed the science as described by the IPCC. I wanted to see if the slideshow bore that out.

Both Hayward’s slideshow and Gore’s are pieces of advocacy, so neither gives a truly balanced view. Nor would one expect balance in this type of presentation. From a scientific viewpoint, the movies are actually comparable: both have much correct science in them, but both also make statements beyond what the scientific consensus can support.

Overall, however, I think Hayward distorts the science to a greater degree than Gore. A good example is his a statement that the latest IPCC report has reduced its estimate of the magnitude of human influence on warming. This is clearly a misrepresentation of science. I don’t think there’s anything in Gore’s movie as misleading.

One of the main points in Hayward’s presentation is that the “science of climate change is not settled.” The implication is that because of this scientific uncertainty action to head off climate change is premature. However, this statement, as appealing as it might sound, shows a gross misunderstanding of uncertainty in science and policy.

In science, important and novel claims are repeatedly tested by independent scientific groups. A claim is only accepted if it passes all of these independent tests — if it meets an exacting and rigorous standard. Because of this, it can take decades for the scientific community to accept revolutionary claims, like the slow movement of plate tectonics.

The reason for this is that accepting an incorrect claim can be quite costly, since it will confuse and misdirect subsequent research and casts doubt on the accumulated body of related prior knowledge.

In policy, however, decisions to take action are typically made with much less evidence. In most cases, waiting decades until all the data are in is simply not an option. In some cases, perhaps, the bar for evidence is set too low. In a recent book, Dick Cheney is quoted as saying:

Even if there’s just a 1 percent chance of the unimaginable coming due, act as if it is a certainty.

As you can see, policy decisions (at least about war!) can be and typically are made with a much lower standard of proof than would be required in a scientific forum.

Which brings us back to climate change. There are significant uncertainties in our knowledge of the climate system. As long as there is much we do not know about the climate, as a scientist I cannot say “the science of climate change is settled.” In fact, the number of scientists working on the climate problem clearly indicates that major scientific problems remain.

When the science is settled, you’ll see scientists moving into other fields, as they did when we finally settled the science of ozone depletion.

But many people, looking at what we do know, have concluded that it’s time to take action now to head off climate change. Thus, from a political standpoint, the science is settled.

By confusing the standards of evidence in these two arenas, Hayward makes an attractive but ultimately flawed argument. The science is not settled, but we know enough to start taking action now.