Q&A on "Hot Topic" Climate Story

Readers responded to “Hot Topic,” a fall 2021 story about GU’s new Climate Center. Brian Henning, director, chimes in.

Francine Haman (Redmond, Wash.)
I’m compelled to comment on the “Hot Topic” article on climate change. On page 20 the article lists “4 Good Reasons to Change Course and Redirect Climate Change.” Point No. 4, “Reduce the negative global impact caused by the U.S. (the largest emitter of CO2 in the world)” is an incorrect statement. China is the larger emitter, having double what the U.S. has with U.S. being second (worldpopulationreview.com).

Dr. Henning: 
It is true that, looking at current annual national emissions, the United States is the second-largest emitter. However, it is not clear that is the best way of presenting the situation. Although China as a country emits more today than the U.S. as a country, per capita, the average person in China emits less than half the average person in the U.S. Further, since carbon is long-lived in the atmosphere it might be better to consider cumulative, historical emissions. In that context, the U.S. is indeed the largest emitter of greenhouse gases; that is, since the start of the Industrial Revolution, we have created the most heat-trapping emissions  (ourworldindata.org).

Greg Jeffrey, Fargo, N.D.
Thank you for the article about climate change. I have a question concerning climate change that no one has been able to answer. The first thing one learns about the scientific method is that one cannot deduce CAUSATION from CORRELATION. Just because warming temps are correlated with increasing CO2, how have scientists deduced CAUSATION from this CORRELATION? Without the ability to control for variables, how did the science community conclude CO2 was the culprit?

Dr. Henning:
The short answer: It’s true that correlation is not causation; however, in this case we have a very solid understanding of how the effects of certain gases work in atmosphere. More carbon dioxide and methane will, overall, lead to more heat within the atmosphere being retained. That said, at the end of the day, scientifically we don’t really know anything with absolute certainty or 100%. All we can do is use our measurements to construct models that are accurate a very high percentage of the time. (A great resource for beginner and intermediate explanations of the greenhouse effect is skepticalscience.com.)

Because I’m a philosopher, I can’t help but also add the following, less short, answer: 

1) The reader asks how scientists “deduce” causation from correlation. The answer is, they don’t. Science doesn’t use deduction in this way. Deduction is a form of logical inference wherein the conclusion necessarily follows from the premises (assuming that the form is valid). For instance, take the following argument. 

If A then, B. 
A. 
Therefore, B. 

This is a logical deduction (it is called modus ponens.) The key here is that, if the premises are true, then B necessarily follows. The conclusion is deduced. Science uses many forms of logical and mathematical reasoning that involve forms of deduction, but, in the end, science is a form of inductive reasoning, not deductive reasoning. Inductive reasoning makes broad generalizations from specific observations. Basically, there are data, then conclusions are drawn from the data. The conclusion is more or less probable. It is not necessary. The stronger the evidence/observations/data, the more probable/stronger the conclusion. But induction cannot ever, in principle, get to absolute certainty. So, the formulation of the reader’s question is mistaken. Science does not and cannot deduce causation from correlation. This is nicely captured in Jiana’s “final words” below when she says that scientists cannot know anything 100%. In other words, there is no absolute certainty in science because, as a form of inductive investigation, it is always making generalizations that are more or less certain (probable) based on particulars. Put differently, you can never go from particular premises to a universal conclusion. 

2) The reader has their finger on an even deeper problem that is the subject of several hundred years of debate within Western thought. It was most famously captured in the work of the 18th century philosopher David Hume. For a clear treatment of the issue, see this encyclopedia entry on Hume and causality and this one on Hume and Kant on causality. Because you aren’t likely to want to wade through all of that, I’ll give you the upshot. Basically, in the 1700s Hume showed that we can never actually “see” causality. We see A hit B and we infer that A caused it, but we don’t actually observe the causality itself. In this way, to use the reader’s terms, all we ever see is correlation. We can never actually observe causality. I know this sounds odd, but after several hundred pages of argument Hume makes an interesting case.

So, what is the point? The point is that, intentionally or not, the reader is using a standard for demonstrating causality that cannot be met.

Thanks, readers, for sending in questions on the topic of climate change!