# Scientific Uncertainty

*Published:* 2007-07-24
*Author:* Lisa Moore

*The author of today’s post, [Lisa Moore](http://www.environmentaldefense.org/page.cfm?tagID=404), is a scientist in the Climate and Air Program.*

I’ve been reading a great book called *[Uncertain Science… Uncertain World](http://www-personal.umich.edu/~hpollack/book.html)* 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](http://www.environmentaldefense.org/climatechangeworkshop/part1/SupportingFiles/ViewerWM7.html) 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](http://www.ipcc.ch/) (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](https://blogs.edf.org/climate411/2007/07/12/human_cause-5/). We must act now to reduce greenhouse gas emissions. The challenge facing us can seem overwhelming, but [we can turn this around](https://blogs.edf.org/climate411/2007/03/28/green_technologies/).

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.