Sea-Tac Just Had Its Hottest Recorded Decade… Ever

By Lester Black, The Stranger

An airplane takes off as the sun sets behind it.We just finished the hottest decade ever recorded at Sea-Tac Airport—by a longshot. The average temperature at the Seattle area’s most watched weather station was 53.8 degrees Fahrenheit this decade, 1.5 degrees hotter than last decade’s average, and a startling 3.6 degrees hotter than the average temperature in the 1950s, when the airport’s earliest weather data was collected.

In addition, the first, second, and third hottest years ever recorded at the airport (2015, 2014, and 2016, respectively) all occurred within the last ten years, according to Joe Zagrodnik, a Washington State University meteorologist who crunched the numbers for me.

What’s going on?

At first glance, Sea-Tac’s weather data seems to be announcing the beginning of a climate apocalypse. But before you trade in your gas guzzler for a bus pass (actually, do that anyway), I should mention that Sea-Tac is not a perfect station to measure our entire region’s weather. No single weather station can measure regional changes and Sea-Tac’s weather has likely been affected by 60 years of nearby urban growth and airport expansion. In addition, when you sample more data points our region actually appears to be warming to a much lesser degree than the Sea-Tac data reflects. By some measures, Washington is actually the slowest warming state in the country.

“This record at Sea-Tac wouldn’t be enough on its own to draw conclusions from,” Amy Snover, director of the UW Climate Impacts Group, said an e-mail. “But the trend is consistent with longer-term trend across the state… region… nation…. and globe… over the last 115 years. Most of the global temperature increases since the 1950s were caused by human activities (emissions of greenhouse gases, primarily by burning fossil fuels).”

In other words, Sea-Tac’s weather is both a harbinger for the sweltering world ahead of us and somewhat of a red herring in understanding the precise nature of our regional weather.

That makes it worth paying attention to.

The Airport Is Getting Hot

There appears to be a clear signal in the average temperature at Sea-Tac across the last 60 years: the airport is heating up significantly.

Five out of the last six decades were warmer than the previous ten years, with the 1950s and 2010s seeing the largest jumps.


During that same 60-year period, global emissions of carbon dioxide and other greenhouse gasses—gases that warm our planet by trapping more heat in our atmosphere—have skyrocketed. Carbon emissions in the 1950s were around 5 billion tons of carbon dioxide per year. Now they are over 35 billion tons per year and rising. There were 316 parts per millon (PPM) of carbon dioxide in our atmosphere when scientists first started measuring it in 1958. It’s now over 400 ppm.

But something else happened at Sea-Tac during that same period of massive carbon emissions: a new region was growing. Millions of people moved into the Seattle metropolitan area during that time and the airport itself expanded and added new runways made of heat-emitting concrete.

Those changes likely affected the weather at the airport, according to Karin Bumbaco, a staff member at UW’s Joint Institute for the Study of the Atmosphere and Ocean and the state’s assistant climatologist.

“Increases in development can definitely impact temperatures in urban areas, and there is some evidence that the addition of a third runway at Sea-Tac in the early 2000s has warmed temperatures, especially in summer,” Bumbaco said in an e-mail.

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