by Kevin Schofield

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This week’s “long read” takes us into the world of climate change and how the nation’s lead agency on climate and weather tracks it.

The National Oceanic and Atmospheric Administration, or NOAA, is responsible for all things weather and climate in the United States: It runs the National Weather Service, supplies forecasts to other government agencies and to the public, and collects and archives atmospheric readings from a collection of tracking stations across the United States. That data is used to improve weather forecasting models, but it is also used to analyze broader climate trends.

A brief word on the difference between “weather” and “climate,” because we often conflate them and especially when talking about climate change. “Weather” is what is happening at any given moment in the atmosphere, whereas “climate” is our general expectations for what the weather will be like over a period of time. To analogize a bit: In your workplace the climate may be hostile, but you likely will still have some good days and some bad days.

NOAA measures the climate, and how it is changing, by averaging the weather over a 30-year period and comparing it with other 30-year periods going back to 1901. Every ten years it generates a new “climate normal” measurement, and it just released the latest one for 1991 through 2020. While there are several measurements included, the two primary ones are temperature and precipitation.

Even though the “climate normal” models for 1981–2010 and 1991–2020 have an overlap of 20 years, there is still a substantial change between the two. Nearly all of the “lower 48” have seen significant warming, with the exception of the Dakotas and eastern Montana.

This follows a trend that has been in place since 1961.

It’s interesting, though, that precipitation follows a very different pattern. While the Southwest has been drying out, much of the Midwest and the eastern seaboard have become wetter. NOAA scientists point out that this is because there are multiple factors that control precipitation beyond temperature. We know this well here in Washington, where we have rain forest on the western side of the Olympic Mountains, much drier areas on the eastern side of the range, and “convergence zones” throughout Puget Sound. But they also note that there are more dimensions to precipitation than just the amount: It can fall as rain instead of snow, and it can come in large downpours with long dry spells in between. We are already seeing how our snowpacks in the Cascades often disappear earlier in the year, even if total precipitation remains the same. Those factors make a big difference in how we need to manage our water supply here.

NOAA also provides a site where we can explore the climate data by city or county, and by month — since climate change can also have different impacts by time of year. It shows some very interesting changes here in Seattle: The city is, on average, 1.1 degrees warmer and 1.85 inches wetter, but it’s not spread evenly across the year.  January’s temperature and precipitation don’t look that different over the last seventy years, but August is getting a little hotter and drier.

Climate Change and the 1991–2020 U.S. Climate Normals

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📸 Featured image is attributed to broombesoom (under a Creative Commons, CC BY-NC-ND 2.0 license).

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