“95% uncertainty”


Last week, the UN Convention on Climate Change was held in Warsaw, Poland. The purpose of the conference was for UN countries to come together to decide on a unified response to climate change.

The Convention was a bit rocky throughout the week. Many pointed to the recent typhoon in the Philippines as a call to action, even though single weather events can’t be linked directly to climate change. Australia’s government voted to repeal the country’s carbon tax and Japan declared it won’t be cutting emissions as much as expected due to its post-Fukushima energy reality. On hearing that news, about 800 conference-goers from frustrated NGOs walked out. 

By all accounts, no one was expecting much from this meeting other than perhaps keeping the lines of communication open for the 2015 Paris Convention, which will hopefully result in an agreement to replace the Kyoto Protocol. The end result was a feeble agreement by which each of the participating countries will individually set their own targets and timeline for carbon emissions reduction.

Why is it so hard to decide on an actionable response to climate change? There are lots of sociopolitical issues in each country that stall the decision-making process. But misunderstanding or lack of communication from the science community can also contribute to a lost sense of urgency.

For decision-making purposes, reports from the Intergovernmental Panel on Climate Change are often the reference point. Every few years, the IPCC has the daunting task of analyzing the full body of climate change literature, then getting thousands of scientists and more than 120 governments to agree on what the science is telling us. The fact that the panel has been able to accomplish this task — not once, but five times — is nothing short of a miracle itself.

However, using the report to take action on climate change has proved more of a challenge. The scapegoat in these instances is often the uncertainty in the science. The latest IPCC report, released this fall, says that the science community is 95% certain that climate change is happening. (I’ll note here that the terminology often ends up being “95% uncertainty”, but really we’re 95% confident that we’ve got the right answer. I mention it to clarify that the IPCC is 95% certain, not 95% uncertain.)

Not everyone is a fan of the IPCC results, though. There are those who distrust the numbers completely. These are generally people who have and will always disagree with what the IPCC says. Their skepticism isn’t groundless; combining uncertainty from so many different experiments is a near-impossible task. Yet for a problem affecting everyone in the world, it’s important to at least try. So to these critics, I can say only that the peer-reviewed literature, a standard of quality,  supports the IPCC results.

The other camp I’ll address are those who believe the numbers, but don’t find them compelling. To some, it’s not enough. Some people would rather wait to take action until we’re absolutely certain that we have this climate change thing figured out. But this view fails to acknowledge one key thing: scientists don’t do certainty. We avoid it like the plague. You may not realize it, but we’re uncertain that gravity is really a thing. We’re uncertain that the sun will rise tomorrow. That’s because we’re willing to admit that we could have missed something. The history of science has shown how this can be the case and over time we adjust our thinking as we get new information. We’re also more than willing to admit that we can’t see into the future.

In common terms, uncertainty means that we don’t know something. We’re not sure. It could go either way. This would be the case if we had no information on the situation.  But scientists have a lot of information about climate change. In science, uncertainty happens on a continuum.We’re not willing to say we have it 100% figured out, but 95% certainty is still pretty darn sure.

Thinking that the presence of uncertainty — even 5% — warrants inaction is not a good idea. In daily life, we’re uncertain about things all the time. We don’t see that there will be a car accident on the way to work or realize in advance that we’re going to trip and break a leg tomorrow. But we know there’s a possibility of those things happening. And given enough time, we know there’s a an even better probability of them happening. So you know what we do? We buy insurance. We leave the house early. We take action now to prevent a worse situation later.

Uncertainty is important. But what’s more important is the level of certainty we have, because it can help us figure out just how much insurance we need. On climate change, we have a lot of certainty. I recently saw an article from the AP that contacted experts in several science fields to see how uncertainty in climate change compared to uncertainty in other phenomena. The article points out that the IPCC is as certain about climate change as they are that cigarettes kill. We’re as sure of climate change as we are of the age of the universe. We’re more sure that climate change is happening than we are that vitamins can make you healthier.

I’ll end this by commenting that uncertainty is a very tricky business. I don’t declare that 95% is the exact level of certainty we have about climate change. In many cases, experts have a tendency to overstate their confidence because it’s impossible to include the infinite number of tiny contributions to uncertainty in any real system. 95% isn’t a fact, it’s an estimate. Some scientists believe that the real confidence level is higher, maybe even 99%. By their measure, 95% is a conservative estimate that counteracts an assumed overconfidence. While there could be small things we’re missing that reduce the 95% confidence number, it’s good to remember that all the big effects are accounted for. So if 95% isn’t quite right, it’s not likely to be far off.

Bottom line: climate change is well-supported by science to a high degree of certainty. If we were this sure there would be a flood next week, we’d buy flood insurance.

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14 thoughts on ““95% uncertainty”

  1. I completely agree with you. There is too much emphasis on uncertainty when in reality scientists are annoyingly uncertain about everything. It’s the people who speak with conviction that we need to be worried about.

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    • Ah, I wouldn’t say the presence of uncertainty is annoying; it’s just a fact of life. :) There will always be uncertainty and I think it’s important to recognize that. As a scientist, I think it’s particularly important to work toward quantifying it. Without uncertainty quantification, there’s just no way to be realistic about ourselves of what we really know and what we still need to work to figure out.

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  2. Your thoughts on climate change are so persuasive, Gail. I especially liked your analogy of being prepared for eventualities by buying insurance, leaving early, etc. That ought to make eminent sense to anyone reading this who ever had doubts about climate change and its possible effects. My own view is that we should be doing something now.

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    • Thanks, Anne. I like to think that the facts themselves are pretty persuasive. I’m glad to be able to share what I know with other people and the idea of buying insurance is one of the better analogies I’ve heard to explain the situation.

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  3. Excellent, Gail, especially the point about uncertainty. Look at medicine as another example–we do our research and seek the treatment that seems most logical or helpful but it is never with 100% certainty. You have a lot of insights and information on the whole issue here and presented in a very reasonable way.

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    • Great example, Meg. Everything in life is uncertain. In the end, we weigh the risk of the adverse consequences and make choices about how to avoid high risk situations. Unfortunately, the future impacts we expect as a result of climate change are looking high risk, but we still can’t decide on a course of action.

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