The darling of the the climate blogosphere for the last two days is an article by Andy Revkin on the silent middle ground in the climate debate. Since I am nothing if not a blogosheep, I felt compelled to follow the pack and weigh in.

The problem I have with the article is that it confuses two separate debates, one scientific (is climate change real?) and one value-based (what should we do about it?). By putting these two issues into the blender, the article confuses rather than clarifies.

Let’s consider the first question: is climate change real?

The scientific consensus on this question has been available for more than 15 years in the form of the reports of the Intergovernmental Panel on Climate Change (IPCC). Its last report detailed what the scientific community has concluded about climate change:

  1. The Earth has warmed about 0.6 deg C over the last 100 years.
  2. Humans are likely responsible for most of the recent warming.
  3. Warming over the next 100 years is likely to lie between 1.4 and 5.8 deg C.
  4. Potentially serious impacts may result.

The vast majority of scientists support this viewpoint. Not only are there not three sides to this debate, there are not even two. There is only one: the IPCC’s. It presents the only valid picture of what the scientific community thinks about the science of climate change.

Let’s consider now the second question: what should we do about climate change?

Given a real risk of serious impacts, should we act immediately? Should we panic? Should we take a Lomborg-ian view and tackle other problems first? Etc., etc., etc.

Questions about action are fundamentally value-based, not scientific. You and I can agree completely on the science articulated by the IPCC but disagree vehemently on what to do about it. An evangelical Christian, for example, can say that we must maintain the Earth as it was given to us, and that means sharp, immediate action without regard to cost; a die-hard economist would say that cost-benefit calculations should determine our actions, and that approach counsels only small near-term actions.

Because questions about action almost always involve value judgments, there is little basis for thinking these questions have right or wrong answers. Attempts to settle these questions through the processes of science are doomed to fail. The only way to settle them is through public debate.

Much of the debate Revkin describes in his article is not over science but over action (though scientists are some of the most vocal participants). The statement by Hansen that we need to act now is a valid policy position, consistent with the IPCC. So is the statement by Wunsch that we should perhaps take less dramatic action, more akin to an insurance premium. The argument here is about values, not science: How risk averse should we be as a society? How do we balance the environment against other goals of our society? Etc., etc., etc.

In policy debates, it is the most extreme positions that get the most traction. These positions are usually the simplest to articulate and philosophically the easiest to defend. In the Iraq debate, for example, the initial positions were to stay the course or withdraw immediately.

The extreme positions tend to be unworkable, and more moderate but harder to defend positions are generally adopted in the end. That’s what we’re seeing in the Iraq debate.

I think that’s what’s also happening the climate debate. Policies of “stay the course” (do nothing about emissions) and “maximal response” (cut emissions deeply, immediately) are both untenable. In response, the debate has begun to focus on reasonable short-term actions. I’m glad to see this, because this is where progress will be made.

The Revkin article would have been a great contribution had it better separated the science from policy debates. There has not been any real debate over the science in several years, perhaps even the last decade. There has been and continues to be broad agreement among scientists about what we know and what we don’t know. The recent evolution is in the political debate. Unfortunately, by combining these questions, the Revkin article does little to clarify the nuances of the debate for the non-expert.