Climate change is something that’s difficult to experience directly. How many people can say, from personal experience, that it feels like the average temperature in your hometown, let alone the globe, has changed by a degree or two over the past century?
Instead, people tend to try to detect climate change on their own from their experience of individual, usually extreme events. For example, “It never seems to get as cold as it used to.” Communicators have learned this, and have taken to emphasizing individual events as evidence for or against climate change.
I call this “the weather trap”. Weather extremes will always take place, no matter how the climate changes. Some will become more frequent, some less frequent. Many weather extremes are so erratic that a statistically significant increase or decrease might not be detectable for many decades, even though the very real monetary consequences from such changes in extremes start accumulating from the get-go. This means that just about any such attempt to link extreme events with climate change is doomed to logical failure.
For example, suppose that climate change has caused 60% of all temperature records to be record highs and only 40% to be record lows. If Person A points out each record high temperature as evidence of climate change, Person B can point out each record low temperature as evidence of no climate change.
Who wins such an argument? It seems to me that both persons come off badly. A person hearing from Person A and Person B would be likely to notice that record lows still happen almost as frequently as record highs, and if the highs are evidence for climate change and the lows are evidence against, the evidence is almost 50-50. Not very compelling, so Person A loses. Still, record lows certainly don’t mean the globe is getting cooler, so Person B looks stupid too.
Person A is on more solid footing saying that record highs are becoming more frequent (if the evidence supports such a statement) or are expected to become more frequent (if the evidence supports such a statement). Still, if Person A wishes to relate such a statement to a particular weather event, he or she had better make sure that such events are increasing at that particular location.
During the 2012 election there was severe drought in Texas. Some filled Person A’s role by implying that Rick Perry’s state was being directly harmed by climate change. Yet, an analysis we published in 2011 showed that rainfall in Texas had increased by 10%-15% over the past century. At best, global warming contributed to drought intensity by increasing evaporation through warmer temperatures.
There’s strong evidence that drought is increasing globally because of climate change, but this does not mean that drought is increasing in every single location because of climate change. According to the latest IPCC report, Texas is one of those locations, but until the observed trend turns around, it’s difficult to be confident about future changes, and even more difficult to conclude that those changes have already started.
Does Person B have any sort of solid position to stand on? Perhaps the most defensible position in pointing out things like record lows is to argue or imply that either (a) record lows are bad things, so global warming wouldn’t be all bad, or (b) since record lows keep happening, global warming can’t be having a substantial impact. Statement (a) is true, while statement (b) requires that all the potential impacts of global warming are measurable by the local change in temperature, and is thus more questionable.
During the current “polar vortex” episode, we’ve seen another trap for Person A: arguing that an extreme event is caused by climate change because a scientific study finds a link between them. As a general rule, a large fraction of apparent links detected by correlation are later found to be spurious, and statistical correlation is the main evidence linking the polar vortex excursion to global warming. Meanwhile there’s other evidence pointing the other way, and most scientists in the field (such as myself) are waiting for physical proof of a viable mechanism connecting the two before they’ll accept that the correlation is physically based.
This is not the only time the press or advocates have trumpeted a connection between severe weather and climate change based on a number of studies that can be counted on one hand (tornadoes have a similarly tenuous link). If the connection turns out to be nonexistent, we will again hear Person B saying scientists got another thing wrong about global warming, when in fact the problem is public officials and the media talking up what is at best a tentative connection.
If you’re a scientist talking about the possible connection between a particular extreme event and climate change, I recommend: (a) wait for a consensus to develop before even mentioning the idea; (b) be specific about whether the connection has been observed or is merely expected; and (c) be specific about whether it’s known that the specific location of the particular extreme event is or should be seeing the frequency or severity change. Even following those guidelines, whatever you say will be picked up and translated by Person A and Person B.
If you’re a member of the general public, you can bet that the truth is a lot more nuanced than what either Person A or Person B is telling you.