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The New Normals: How U.S. Weather Has Changed Since 1900

The National Oceanic and Atmospheric Administration last week issued its latest “climate normals”: baseline data of temperature, rain, snow and other weather variables collected over three decades at thousands of locations across the country.

Updated every 10 years, the normals are used by TV meteorologists when they tell you that today’s blisteringly high temperature was 10 degrees above normal for that location and date, for instance, or that a single heavy downpour brought more rain than is typical for an entire month.

The normals — which are available on annual, seasonal, monthly, daily and even hourly timescales — are invaluable to farmers, energy companies and other businesses, water managers, transportation schedulers and any one who plans their activities in coming weeks or months based on what is likely, weather-wise. They come in handy, too, if you want to know how to pack for Oshkosh, say, in October, or if you’re past the last frost date and wondering if it’s safe to put out some tomato seedlings.

“What we’re trying to do with climate normals is put today’s weather in the proper context,” said Michael Palecki, who manages the project at NOAA’s National Centers for Environmental Information.

Because the normals have been produced since 1930, they also say a lot about the weather over a much longer term. That is, they show how the climate has changed in the United States, as it has across the world, as a result of emissions of heat-trapping gases over more than a century.

The change is especially drastic between the new normals and the previous ones, from 2010. “Almost every place in the U.S. has warmed,” Dr. Palecki said.

The temperature results are in keeping with what we’ve long known: that the world has warmed by more than 1 degree Celsius (about 1.8 degrees Fahrenheit) since 1900, and that the pace of warming has accelerated in recent decades.

You can check out the interactive maps and read more on the NY Times website here.