Last week, the world watched in horror as Hurricane Dorian ripped though the Atlantic, leaving devastation in its path, and as usual, debates online have swirled around the same question that arises every time there is a major weather event, “is this climate change?” Many people point to storms like Dorian as evidence of climate change and the very real dangers it poses, but others cry foul and insist that climatologists and science-advocates are being hypocritical and inconsistent. “Whenever we point to a blizzard or cold front as evidence that the climate isn’t changing,” they say, “you all accuse us of cherry picking and shout that ‘weather isn’t climate,’ but when there is a hurricane or a heatwave, suddenly you’re convinced it’s global warming.” This accusation of a double standard deserves some discussion, because there is a small kernel of truth to it, but, as usual (always?) there are key pieces that climate change contrarians are ignoring. So, let’s look at this for a few minutes.
Let’s start by dealing with the part that contrarians get right. If someone’s entire argument is, “it was hot today, therefore climate change is real” or “there was a big heatwave, hurricane, drought, etc., therefore climate change is real” then they are, in fact, conflating weather with climate. I will admit that this line of reasoning is no different than saying, “it was cold today, therefore climate change isn’t real.” However, and I can’t stress the importance of this enough, that is almost never what I see people doing. Rather, the argument usually points to a current weather event as the latest in a trend of changing weather patterns. This is a key distinction for several reasons.
First, we need to consider why it is problematic to conflate weather and climate. Weather is what happens over a short period of time, whereas climate refers to long term trends and patterns. Thus, an individual storm, cold front, etc. is weather, but a pattern of increasing storms, heatwaves, etc. over time is climate. So, when people use a storm like Dorian as an example of the latest event in a trend of changes, they aren’t conflating weather and climate, rather they are talking about climate. When we look at the trends, we see that the average intensity and the proportion of hurricanes/cyclones that are very powerful has increased over time, just as climate models predicted (see note 1: Emanuel 2005; Elsner et al. 2008; Holland and Bruyere 2014; Walsh et al. 2016). There is also a trend of hurricanes hitting further from the equator (Kossin et al. 2014), and a pattern of storms increasingly “stalling” (just as Dorian did; Kossin 2018; Hall and Kossin 2019; see note 2). So, it is completely valid to talk about a storm like Dorian in that context. By the same token, it is completely right and proper to bring up climate change when a heatwave occurs, because there are strong, decades-long trends of heatwaves increasing in frequency, duration, intensity, and the extent of area they affect (Klein Tank and Konnen 2003; Della-Marta et al. 2007; Russo et al. 2014; Tanarhte et al. 2015; Perkins et al. 2012; Habeeb et al. 2015). In contrast, saying “this part of the world experienced a record cold this week” and using that as evidence against climate change is using an isolated weather event, rather than a climate trend. There is no trend of increasingly cold winters. Rather, there is a global trend of increasingly warm temperatures. Indeed, as of the writing of this post (2019), all five of the five hottest years on record occurred in the past five years, and 18 of the 20 hottest years happened in the past 20 years (based in NASA’s data; the remaining two hottest years occurred in 1997 and 1998). There is a strong trend of increasing temperatures, which is why we are justified in bringing up climate change when we experience record-breaking temperatures (no, the warming hasn’t paused, that’s a myth).
This brings me to my second, and closely related, point: the nature of cherry picking. Cherry picking occurs when you isolate and cling to any pieces of evidence that conform to your beliefs while ignoring a (usually larger) body of evidence that disagrees with you. Hopefully from the paragraph above you can see where I am going with this. Citing a particular cold front, blizzard, etc. as evidence against climate change is, by definition, cherry picking, because it is using isolated events rather than trends, and it is ignoring the big picture of increasing global mean temperatures. Conversely, talking about heatwaves, hurricanes, etc. in the context of their trends is not cherry picking. It is literally the opposite of cherry picking because it is about trends and the big picture. On that note, I want to go down a brief side tangent to point out that using regional data to argue against climate change is also cherry picking. No one ever said that every part of the planet will be warmer all the time. Rather, we are talking about global patterns and global temperatures. Citing a few cherry-picked locations ignores that big picture.
By way of example, it would be crazy to isolate one person who smoked their whole life and never got cancer and say, “see, smoking doesn’t cause cancer because they smoked and are fine.” That would obviously be cherry picking, and it would be nuts because it would ignore the overarching picture of the strong trend of smoking increasing cancer risk. That is, however, exactly what climate change deniers are doing when they cherry pick a particular cold front, blizzard, ice sheet, etc.
Now, at this point, someone is inevitably thinking, “yeah, but you can never actually say that a particular cyclone, heatwave, etc. was caused by climate change, so it’s still deceptive to try to blame climate change when one happens.” My response to this is, again, two-fold. First, in many cases, we can actually use statistical techniques to show that certain weather events were so extraordinary that they were unlikely to have occurred naturally. For example, see the 2003 heatwave that caused over 70,000 deaths in Europe (Schar et al. 2004; Stott et al. 2004; Robine 2008). Similarly, studies showed that climate change very likely contributed to the extreme rainfall observed during Hurricane Harvey in 2017 (Risser and Wehner 2017; van Oldenborgh et al. 2017; Wang et al. 2018). There are many storms like this where we can, in fact, say with a high degree of confidence that climate change contributed to them (note: science never deals in 100% confidence).
The second consideration (again, related to the first), is that although we can never say with 100% certainty that a given event was caused by climate change, we can say that climate change is increasing them or their intensity, so we are justified in using them as examples of the dangers of climate change, and whether or not climate change caused any one particular storm is irrelevant, because we know the effect climate change is having in general.
Let’s go back to smoking as an example. Smoking causes cancer. This is well-established. However, that does not mean that everyone who smokes will get cancer, nor does it mean that everyone who gets lung cancer smoked. As a result, we can never say with 100% certainty that any particular case of cancer was caused by smoking, but that is really beside the point. The point is that there is a general trend of smoking increasing cancer risks. Thus there is a high probability that a smoker’s cancer was connected to their smoking, and it makes perfect sense to show people pictures of cancerous lungs and stories of people who suffered from lung cancer after a history of smoking. To put that another way, we can never point to an individual and say with 100% certainty that smoking caused their cancer, but we can point to them as an example in a general trend that we should take seriously. The same is true with climate change. Whether or not a particular storm was definitely caused by climate change is beside the point. The point is that climate change is making intense hurricanes more common, heatwaves more intense, frequent, and long, droughts more common in some areas while floods increase in others, etc. These are serious issues that need to be treated accordingly, and it is completely right and proper to talk about climate change when these extreme weather events occur.
Note 1: It is important to clarify that it is the average intensity and proportion of hurricanes/cyclones that are high intensity (e.g., category 4 and 5) that is increasing, not the total number of hurricanes/cyclones. This is consistent with model predictions.
Note 2: There is a general pattern of increasing hurricane stalling, but there is some disagreement among scientists about the cause. Several models did predict a slowdown in hurricane transition speed due to climate change, but others predicted no change. So not all scientists agree that climate change is the cause (despite what many think, scientists love to argue and don’t automatically assume that everything is being caused by climate change). I personally think that the evidence more compelling suggests that climate change is the cause, but I will wait for more data before reaching a verdict, and I wanted to include this note since the evidence does not point to climate change as conclusively as it does on other issues (despite what many think, I really do care about accurately portraying evidence and the scientific literature).
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