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Certain And Confident: Predicting The Future In A Climate-Changing World

Nov 13, 2017
Originally published on November 10, 2017 1:36 pm

This last week brought big news in the struggle over climate change and climate science.

First, there was the announcement that Syria was signing on to the Paris Agreement, making the U.S. the only nation on the entire planet to reject it. Even more important, however, was the publication, released by the White House, of the Climate Science Special Report (CSSR). Coming in at a whopping 470 pages, the report was prepared by the nation's top Earth scientists and its message was pretty blunt.

Science is certain that the climate is changing and it is confident that human activity is the cause.

I am going to leave you to figure out how the administration can square its denial of climate change science with their own top scientists' full-throated recognition of its seriousness. What's more important for us today is the report itself.

That's because I, dear reader, am in your service. And in that service I am going to be putting aside getting through Season 2 of Stranger Things to read all 470 pages of the CSSR (including its thrill-packed appendices with titles like "Model Weighing Strategies"). I'm doing this so I can see, and report on, the exact state of the sprawling human achievement we call "climate science."

Now, the first thing I can tell you is that you should read the report, too (download it here). OK, you don't have to read all 470 pages. Just pages 3 to 8 in the section Guide to the Report and then the Executive Summary from pages 10 to 34. That would be enough. The Executive Summary, in particular, is really well laid out with some cool graphics. I learned a lot from it.

See, if you read just those 29 pages you'll come across something utterly remarkable that is not just about climate science. Instead, the report shows us something about science as a whole.

In the Guide to the Report, the authors provide a detailed roadmap for how they are going to assess the claims they themselves will be making. In other words, they give tools to judge how much weight or confidence you can have in those claims. They also give a scale for how likely the claims are. This means how certain you can be about the truth of those claims.

If this distinction seems weird, let's look at how the report defines these things.

  • Confidence [is] the validity of a finding based on the type, amount, quality, strength, and consistency of evidence (such as mechanistic understanding, theory, data, models, and expert judgment); the skill, range, and consistency of model projections; and the degree of agreement within the body of literature.

  • Likelihood, or probability of an effect or impact occurring, is based on measures of uncertainty expressed probabilistically (based on the degree of understanding or knowledge, e.g., resulting from evaluating statistical analyses of observations).

This is not the first time this kind of thing has been done. But with the new report in the news now, it's worth reflecting for a moment on these definitions because they lie at the root of how all science works, why it works and why science is so valuable to successful societies.

Science does a lot of things. It shows us cool things about the universe, like black holes and DNA. But it also gives us some ability to predict and control the world. This is useful in a lot of ways like, say, not dying in a hurricane that you didn't know was coming.

But as Yogi Berra so famously said: "Prediction is hard, especially about the future." So what the CSSR gives us is an explicit scale for both confidence and likelihood that it applies to every scientific claim it is making. For confidence, that scale ranges from very high to low. For likelihood, the scale ranges from virtually certain to exceptionally unlikely.

Here are two examples from the report. The first relates to the basics of climate change and the second relates to the more contentious issue of storms in a climate-changing world.

  • "Many lines of evidence demonstrate that it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. Over the last century, there are no convincing alternative explanations supported by the extent of the observational evidence. Solar output changes and internal natural variability can only contribute marginally to the observed changes in climate over the last century, and there is no convincing evidence for natural cycles in the observational record that could explain the observed changes in climate. (Very high confidence)"

  • "For Atlantic and eastern North Pacific hurricanes and western North Pacific typhoons, increases are projected in precipitation rates (high confidence) and intensity (medium confidence). The frequency of the most intense of these storms is projected to increase in the Atlantic and western North Pacific (low confidence) and in the eastern North Pacific (medium confidence)."

From my standpoint, these paragraphs show something wonderful. Here is science being totally honest about what it thinks it knows and what it's still not sure about. Did humans change the climate? Yeah, that's extremely likely. Can we say natural cycles are not the cause? Yeah, we have very high confidence in that statement. So, if you want to go out and yell from the hills that science shows us the climate is changing because of human activity, you have science's blessing.

But what about climate change increasing the frequency of intense storms? Well, that might be happening. The thing is, we don't have a lot of confidence that it is happening in the Atlantic. We are, however, a little more certain about it happening in the North Pacific. So, if you want to go out and yell from the hills that science shows climate change is making more frequent intense Atlantic storms, then you are on more shaky ground. We (meaning science) aren't confident in that conclusion yet.

The cool thing about this is it makes explicit what happens everyday in every science. It shows us explicitly how science works. Most folks don't see this balance of confidence and likelihood because most of us researchers carry it via internal and un-explicit maps about what we think we know about our fields and what we think is shaky.

Most important, the CSSR shows science for what it is — a human endeavor done by human beings. At any given moment, it represents the collective understanding of that community. It is not infallible by any means but it represents a process that has worked pretty damn well for us (know anyone with polio?).

That's why the CSSR report is such a valuable read. It's not just about one research field (i.e. Earth Systems Science). Instead, it's also a primer on how science works when it overlaps with the human need for making intelligent, informed bets on our future.

No one can know the future, but with this amazing tool called science we sure as heck can have more confidence and certainty as we face it together.


Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester and author of the upcoming book Light of the Stars: Alien Worlds and the Fate of the Earth. His scientific studies are funded by the National Science Foundation, NASA and the Department of Education. You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4

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