The temperature anomaly at the local station level is similarly huge at SeaTac airport, Portland International Airport and New Westminster (nr. Nonetheless, the magnitude of the regional anomaly is more than 5✬ above the previous record. There is a real trend of about 4✬ over the last 70 years – roughly 3 to 4 times the trend in the global mean temperature. But the question is whether the temperature extremes are being made substantially more likely by underlying climate changes.įirst, look the maximum annual daily temperature in the region (according to the ERA5 reanalysis for the historical data and the actual weather forecast analyses since June 1st). A large ‘omega’ pattern (so-called because of the resemblance to the Greek letter ) set up by a Rossby wave breaking event, intersecting with the topography and the warm temperatures to the south-west that were advected to the PNW. Using only data from before 2021, an anomaly this large is estimated to never occur!Įveryone is agreed that the specific synoptic situation is unusual. Using various methods to construct the return time for this event, they show that even in today’s climate this was a one in 400 yrs or longer event. In the paper, they show that this event was truly exceptional in the temperature statistics in the region and specifically in Vancouver, Seattle and Portland, but that the geopotential height anomaly (one measure of the ‘heat dome’ or the ridging) was not that far off from the underlying trends. Their preprint (Philip et al.) is available here. For the specific situation in the Pacific NorthWest at the end of June, we now have the first attribution analysis from the World Weather Attribution group – a consortium of climate experts from around the world working on extreme event attribution. It’s been clear for at least a decade that global warming has been in general increasing the intensity of heat waves, with clear trends in observed maximum temperatures that match what climate models have been predicting.
Summary: It was almost impossible for the temperatures seen recently in the Pacific North West heatwave to have occurred without global warming.
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