I was math nerd as a kid. And yes, that explains a lot about me.
I think what originally attracted me to math was the objectivity of the subject. Its rules were solid and unwavering. No matter what, seven minus five equals two. I guess I like consistency.
That might be why I find the mathematical field of probability so curious. It combines the ordinary objectivity of mathematics with uncertainty and chance. What does math say about whether a flipped coin will land on heads? Only that there is a fifty percent chance. It cannot, however, tell you what actually will happen when you flip the coin.
One of the fundamental principles of probability is “expected value.” This concept is best demonstrated by an example. Let’s suppose that I had a bag filled with tiles numbered 1 to 100. If you reach into the bag and pull out any number between 1 and 97, you win $100. If, however, you pluck out 98, 99 or 100, you don’t win anything. What is the expected value of your opportunity to play this game?
The math formula is fairly simple. You multiply the potential value, or “reward,” by the percentage chance that such value will be realized (or that you will win the reward). In this case, picking 97 different numbers out of 100 is a win, which is a 97% chance (expressed as .97 mathematically). When you multiply .97 by the $100 reward, you get an expected value of $97. You’ll never actually win that amount – you’ll either win $100 or $0. But the expected value does allow you to evaluate how beneficial (or how costly, if you are dealing with costs instead of benefits) the thing is that might or might not happen.
Whether you like math or not, you’re probably about ready for me to stop talking numbers and make a point. Fair enough. My point is that I think probability has a lot to teach us about how we think of climate change.
So much of the controversy surrounding climate change in the United States centers on whether or not climate change caused by humans is “real.” I find this characterization to miss the mark.
What is “real” is that global emissions of carbon dioxide have increased steadily over the last sixty years as a result of human consumption of fossil fuels (call this “Fact A”). At the same time, the parts per million of carbon in the atmosphere has increased (“Fact B”). It’s also factual that global temperatures have increased over the same period (“Fact C”).
The probability that Fact A causes Fact B, which in turn causes Fact C, is how we can judge whether or not humans are primarily responsible for climate change. And the community of climate scientists, as represented by the International Panel on Climate Change, currently believes that it is “extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”
So here’s the rub. When climate change deniers find new evidence that suggests humans might not be driving climate change, that evidence cannot “disprove” anthropogenic climate change. Instead, the evidence might only slightly reduce its probability, from “extremely likely” to a bit less than that. Allow me to explain, once more using my hypothetical bag of tiles….
Now, instead of winning $100, assume that the worst of climate change’s negative impacts (drought, intense storms, spread of disease, shocks to the global economy, etc.) will happen if you draw tiles 1 through 97. In other words, you’ll lose. I would say that the expected costs in that situation are really high, and you probably don’t want to reach into the bag.
What if we changed the game slightly, and now those bad things will only happen if you draw tiles 1 through 95. Perhaps new evidence on anthropogenic climate change has reduced scientific consensus slightly, making 96 and 97 “safe” numbers in this hypothetical. This evidence could change the probability, but it would not eradicate all of the “losing” numbers. Does this hypothetical new evidence make you feel much better? I didn’t think so.
Folks, the expected costs of climate change are immense regardless of whether anthropogenic climate change is “extremely likely” or just “very likely.” Which is why it’s so important that we do all we can now to fix the problem.