Scientific Uncertainty

The author of today’s post, Lisa Moore, is a scientist in the Climate and Air Program.

I’ve been reading a great book called Uncertain Science… Uncertain World by Henry Pollack – a readable and engaging discussion of decision-making in the face of uncertainty. Pollack argues that decision-makers use uncertainty as an excuse for inaction, when in fact it should be a stimulus for creativity and progress.

How sure do you have to be that something will happen to act on the possibility?

We don’t give it much thought, but we take action in the face of uncertainty all the time. We’re not sure we’ll get into a car accident, but there’s a small chance we will so we wear our seat belts. And though we may never need it, we buy major medical insurance. We act on these possibilities, though they’re unlikely, because the consequences, if they occur, are severe.

Yet scientists are held to a different standard. Some people feel that if scientists aren’t 100 percent certain about something, there’s no need to take action – even when there is a 90 percent chance that inaction will lead to catastrophe. Why?

Bill used a great analogy to explain this in a Webcast for teachers in Tennessee. (The section on scientific uncertainty begins about 3 minutes into the video.) He says that some people think of scientific knowledge as a house of cards – if one piece is taken away, the whole house comes down. That is, one uncertainty about climate change means none of the science can be trusted.

In fact, scientific knowledge is more like a jigsaw puzzle than a house of cards – a jigsaw puzzle where you don’t have the box top. As you fit the pieces together, a picture begins to emerge. You may not know all the details, but enough pieces are in place to leave no doubt what the big picture is. That’s where we are now with climate change. The big picture is clear, and the debate is only about individual pieces here and there. Just because scientists don’t know everything about a particular topic doesn’t mean they don’t know anything about it.

In our everyday lives we act based on incomplete information as a matter of course – to the point that we don’t even think about it. But for scientists, uncertainty is top of mind. They’re trained to notice what’s certain and what’s not so they can design useful studies. That’s why they spell out in such exquisite detail what they don’t know about any given topic. And that’s why the IPCC report (indeed, any scientific report) uses such careful language. Sometimes, all that careful language can obscure aspects of a topic that are settled.

Unlike a car accident, which is serious but unlikely, global warming is both serious and likely. In fact, the clear picture that has emerged from decades of research is that it’s already happening. We must act now to reduce greenhouse gas emissions. The challenge facing us can seem overwhelming, but we can turn this around.  

So the next time someone tells you that global warming isn’t a certainty so there’s no reason to act, ask them what the probability of an accident has to be before they’ll wear a seat belt.

This entry was posted in News. Bookmark the permalink. Both comments and trackbacks are currently closed.


  1. kenzrw
    Posted July 24, 2007 at 5:27 pm | Permalink

    Another good article Lisa. I also liked your soot article.

    The only thing I can say here is that, yes, we should take the ‘insurance policy’ to cut our carbon emissions and pollution – that’s good policy regardless of global warming – but at the same time, we should never say that ‘the science is settled’ on anything. Always keep studying, while at the same time taking action. People saying that the science is settled is what has always angered me about the warming discussions and that’s one reason many in the general population don’t take the warming serious enough (like they should).

    We all need to keep at least a small part of our minds open on any subject, and keep looking for other evidence of global warming, even though it seems certain that we’re causing a lot of it. You never know. Also we need to keep looking at totally unbiased temperature reporting around the world to verify the warming and not change methods of determining temperatures to fit the current scientific way of thinking (that’s always a possibility I think).

    Also, we need to highlight that some parts of the planet may indeed be getting cooler (like some southestern US states) and that all should look at the bigger picture, like another article on 411 said. It’s hard for some to believe in global warming with you have record cold in April, for instance.

    Thanks for listening. (Ken – retired meteorologist, who looked at extreme weather events almost every year somewhere on the planet for 32 years)

  2. K.C. Weber
    Posted July 24, 2007 at 8:59 pm | Permalink

    I agree with Ken above.

    Also using your puzzle analogy, I feel that man’s contribution to global warming is only part of the puzzle. It is a very real part. But there are still many, many pieces missing. I feel that ignoring other things that contribute to global warming can be just as deadly as ignoring man’s contribution to it. We need to fit the rest of the puzzle together as well as looking at what we have already. If we ignore the other factors, it could be serious and deadly as well.

    K.C. Weber

  3. Posted July 25, 2007 at 2:57 pm | Permalink

    I just got a call from author Henry Pollack, who noticed this post. He alerted me to another essay he wrote recently about scientific uncertainty. It’s available here [PDF].

    In it he makes another analogy about scientific uncertainty and climate change: “There is a tendency to focus on the weakness of the parts rather than the strength of the whole, supposing that if a single piece of evidence can be discredited, the entire construct will fall like a house of cards. In fact, discrediting a single line of evidence is more like snipping a strand in a net hammock—the hammock continues to be supported by the many strands that remain intact. The scientific evidence for climate change in the natural world is compelling in its totality although individual pieces of the story may indeed be open to some question.”

    Thanks Dr. Pollack!

  4. K.C. Weber
    Posted July 25, 2007 at 4:18 pm | Permalink

    Dear Lisa,

    Yes, your analogies are excellent. And you are right in the fact that we do need to act using the knowledge that we have. Mankind does need to take better care of the environment, and we do need to take action to counteract damage we are doing.

    But, at the same time we can’t limit our action to one point of view, and one only. In global warming we need to be aware and act on all causes of global warming, not just one.

    Using your hammock analogy, the view of man’s contribution to global warming contributes a certain number of strands to the solution, and holds up with a certain amount of support. But if the hammock is not complete, the support is weak.

    Knowing ALL of the causes of global warming adds more strands to the hammock and provides more support for more solutions that we need to take.

    More complete knowledge adds more strands and provides more complete knowledge of actions that we should take.

    K.C. Weber