The big front page story in the Seattle Times today, both online and in print, is about how climate change has caused the death of a 72-year-old pine tree in the University of Washington arboretum. Unfortunately, the underlying premise of the story is false, representing another unfortunate example of exaggerating the impacts of global warming.
The writer of the story, Lynda Mapes, could not have been more explicit:
The cause of death was climate change: steadily warming and drier summers, that stressed the tree in its position atop a droughty knoll.
So, let’s check the data and determine the truth. My first stop was the nice website of the Office of the Washington State Climatologist (OWSC), where they have a tool for plotting climatological data. Here is the summer (June-August) precipitation for the Seattle Urban Site, about a mile away from the tree in question. It indicates an upward trend (increasing precipitation) over the period available (1895-2014), not the decline claimed by the article.
Or let’s go to the Western Region Climate Center website and plot the precipitation for the same period, considering the entire Puget Sound lowlands (see below) using the NOAA/NWS climate division data set and for June through September. Very similar to the Seattle Urban Site. Not much of an overall trend, but there is some natural variability, with a minor peak in the 70s and 80s.
It is also important to note that summer precipitation is relatively low in our region—most our precipitation arrives in four months from late fall to midwinter. Looking at annual precipitation (see below), we find the same story: modest upward trend in precipitation.
So the claim that summers in our region are drying is simply false. Busted.
So what about temperature? Let’s examine the maximum temperature trend at the same Seattle Urban location for summer (June through August). There is a slight upward trend since 1895 by .05F per decade. Virtually nothing.
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