Abstract
The 2021 Pacific Northwest heatwave featured record-smashing high
temperatures, raising questions about whether extremes are changing
faster than the mean, and challenging our ability to estimate the
probability of the event. Here, we identify and draw on the strong
relationship between the climatological higher-order statistics of
temperature (skewness and kurtosis) and the magnitude of extreme events
to quantify the likelihood of comparable events using a large climate
model ensemble (CESM2-LE). In general, CESM2 can simulate temperature
anomalies as extreme as those observed in 2021, but they are rare:
temperature anomalies that exceed 4.5σ occur with an approximate
frequency of one in a hundred thousand years. The historical data does
not indicate that the upper tail of temperature is warming faster than
the mean; however, future projections for locations with similar
climatological moments to the Pacific Northwest do show significant
positive trends in the probability of the most extreme events.