Estimating the dollar cost of climate change from a single extreme event is harder than it looks. Researchers use extreme event impact attribution (EEIA) to compare an actual hurricane or heat wave with a hypothetical version of the same event in a world without human-caused warming. But the answer depends on which question they ask: whether climate change made the event more likely, or whether it made the event more damaging.
Those two approaches can produce strikingly different numbers. For Hurricane Harvey in 2017, which caused roughly $90 billion in damages, a frequency-change approach attributed 75% of the costs to climate change, while an intensity-change approach attributed only 15%. That gap might suggest one method is flawed, but a new framework introduced by Match et al. shows that both approaches can be consistent when applied across many events over time.
The authors define consistency as a match between the total costs attributed to climate change by EEIA and the actual excess costs incurred. Because both frequency- and intensity-based methods can meet this standard, the researchers conclude that the cost of climate change for any individual event is inherently ambiguous. They argue that no technical breakthrough or perfect knowledge of climate and society can remove that ambiguity, which may limit how well EEIA can guide adaptation, recovery, or litigation.