Last May, the temperature in Pittsburgh swung wildly – from near frost to almost 80 degrees.

St. John: “This is much more variability than I remember in the past.”

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That’s blogger Kate St. John, who wondered if this wild weather was caused by climate change. David Titley, a meteorologist at Penn State, says it’s a complicated question because St. John is pointing to weather, not climate.

Titley: “Weather is kind of what you have. It’s what we’re experiencing yesterday, today, tomorrow.”

Climate is weather averaged over a long time. Titley uses a poker analogy to explain:

Weather - the cards you're holding in your hand. Climate - the deck from which they got dealt. Click To Tweet

Titley: “Weather is the cards that you’re holding in your hand today, and climate is the deck from which those cards got dealt, and climate change is somebody slipping another ace in there.”

With an extra ace, a royal flush is more likely, just as climate change increases the odds of extreme weather. But tying specific events to climate change is difficult. So Titley is developing what he calls a “weather weirdness index.”

Royal flush cards

By comparing the output of a computer model of a world without global warming, to actual weather events, he hopes to soon answer if events such as Pittsburgh’s wild weather would’ve been likely to occur without human-caused climate change.

This segment of Climate Connections was produced in partnership with ISeeChange.

Reporting credit: ChavoBart Digital Media and iSeeChange/Kara Holsopple (The Allegheny Front).
Photo: Copyright protected.

More Resources
Penn State Center for Solutions to Weather and Climate Risk

Other weird weather stories:
‘Warm blob’ in Pacific Ocean linked to weird weather across the U.S.
World experiences month of weird weather
Warm Water and Strange Weather May Be Connected

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