This is a post that I’ve been thinking of writing, but have been somewhat reluctant to start. It’s mostly because it relates to something said by Roger Pielke Jr, so could end up being a bit of same ‘ol same ‘ol, which I’ve become rather tired of. However, it’s an interesting issue, and I’m not entirely sure that I’m right, so I’ll have a go.
Research keeps accumulating that shows that so far at least, the rising costs of weather disasters are not a result of weather extremes that have become more common or intense due to climate changes resulting from the emission of greenhouse gases
Now, I think the above is probably strictly correct. We probably have not been able to definitively demonstrate that the rising cost of weather disasters can be formally attributed to the human emission of greenhouse gases. However, I think this is mostly the wrong way to consider this, and I’ll try to explain why.
Let’s start at the beginning. We’re emitting greenhouse gases into the atmosphere. These greenhouse gases accumulate in the atmosphere. Their increase reduces the outgoing longwavelength flux, producing a planetary energy imbalance. This means that energy accrues in the climate system, causing it to warm.
Now, even if we do observe warming, we can’t necessarily claim that it is due to our emission of greenhouse gases. However, as this Realclimate post explains, we can do attribution studies to determine the most likely causes. However, it’s not as simple as observating that it is indeed warming; it requires some kind of model and also requires considering how what we expect from the different possible causes compares to the actual observations. In particular, the different possible causes produce different spatial, and temporal, patterns of warming, which can then be used to determine the most likely cause of the observed warming. Having now done this type of analysis, we are pretty confident that most of the observed warming is anthropogenic.
What are the consequences of this anthropogenically-driven warming? We obviously expect an increase in the frequency and intensity of extreme heatwaves. We also expect the hydrological cycle to intensify, which essentially means more evaporation and, consequently, more precipitation. In particular, we expect an increase in the frequency and intensity of the most extreme precipitation events. We also expect an increase in the frequency and intensity of some of the more extreme weather events, such as tropical cyclones.
Can we actually formally attribute changes in some of these extreme events to anthropogenic emissions? I think this is actually quite tricky, partly because the events are extreme and, therefore, rare. We don’t therefore have enough suitable data to make formal attribution claims (I may be wrong about this, so happy to be corrected). However, I think we do have evidence for an increase in the frequency and intensity of extreme precipitation events and heatwaves. We also have evidence for an association between increased sea surface temperatures and an increase in the frequency and intensity of tropical cyclones (and an understanding of why). So, the observations appear consistent with what would be expected.
In some cases, climatic events do damage that we can quantify in terms of how much this would cost to repair. Typically, these are the rare extreme events, not all of which do damage, which makes the events that do damage even rarer. Hence, formally attributing this to anthropogenic emissions is very difficult. Furthermore, there are many factors that could influence the scale of this damage. It could increase partly because there are now more valuable assets in the way. On the other hand, it could be lower than it might otherwise be because the infrastructure is now more able to withstand the impact of these events.
However, does this really matter? Do we need a formal attribution study to be quite confident that an increase in the frequency and intensity of extreme precipitation events will likely impact flooding? That increased evaporation and warmer weather will likely impact droughts and wildfires? That increased sea surface temperatures will intensify extreme tropical cyclones and make these more damaging if they impact populated coastal areas?
I don’t really think so; these don’t seem to be a particularly controversial inferences (they probably are, but it’s not clear why). Of course, that we expect our emission of greenhouse gases into the atmosphere to ultimately influence the cost of weather-related disasters doesn’t immediately tell us what we should do. However, recognising this seems more relevant than highlighting that we haven’t yet formally attributed increases in weather related damage costs to our emissions of greenhouse gases, especially since the latter could be true even if anthropogenically-driven warming has indeed lead to an increase in the cost of weather related disasters.