WEBVTT - BrainStuff Classics: Do We Need to Redefine the Four Seasons?

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<v Speaker 1>Welcome to brain Stuff, a production of I Heart Radio.

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<v Speaker 1>Hi brain Stuff, I'm Lauren vogel Bomb and this is

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<v Speaker 1>another classic episode from our archives. The seasons are in

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<v Speaker 1>the midst of changing, but they're not changing quite the

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<v Speaker 1>same way that they used to. Is it time to

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<v Speaker 1>redefine them? Hey, they're brain stuff Lauren vogel Bomb here.

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<v Speaker 1>If you live in Earth's middle latitudes, you're accustomed to

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<v Speaker 1>experiencing four traditional seasons winter, spring, summer, and autumn, also

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<v Speaker 1>known as fall. That means that existence in the two

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<v Speaker 1>bands of latitude stretching around the planet from thirty to

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<v Speaker 1>sixty degrees both north and south of the tropics, offers

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<v Speaker 1>a lot more variety weatherwise than on the equator, where

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<v Speaker 1>there's basically a hot, dry season and a hot, rainy season.

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<v Speaker 1>It's a similar story for the upper latitudes, whose residents

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<v Speaker 1>get a cold winter with long dark nights and a

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<v Speaker 1>slightly less cold summer with longer daylight. To be technical

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<v Speaker 1>about it, there are actually two different ways of defining

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<v Speaker 1>the seasons, the astronomical definition and the meteorological definition. The

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<v Speaker 1>astronomical definition is based upon change in the length of

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<v Speaker 1>days that's caused by the relative tilt of the Earth's

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<v Speaker 1>axis as it revolves around the Sun. So in that system,

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<v Speaker 1>winter is the time between the winter solstice, the shortest

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<v Speaker 1>period of daylight of the year, which occurs around December

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<v Speaker 1>twenty two, and the vernal or spring equinox, when day

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<v Speaker 1>and night are roughly equal, which occurs around March twenty one.

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<v Speaker 1>Spring then lasts from the vernal equinox to the summer solstice,

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<v Speaker 1>which is the longest daylight period of the year and

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<v Speaker 1>happens around June. Summer runs from then until the autumnal

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<v Speaker 1>equinox on September twenty three, another day when light and

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<v Speaker 1>darkness are equal. Then autumn continues until the winter solstice.

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<v Speaker 1>The meteorological method, on the other hand, has been around

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<v Speaker 1>since at least the mid nineteen hundreds and is a

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<v Speaker 1>lot simpler. The year is divided into four seasons by

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<v Speaker 1>calendar months, so that winter is December January February, spring

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<v Speaker 1>is March April May, summer is June July August, and

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<v Speaker 1>autumn is September October in November. Study conducted by climate

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<v Speaker 1>researcher Kevin Trenberth found that the simpler meteorological definition more

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<v Speaker 1>closely agreed with observable weather in the continental regions of

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<v Speaker 1>the northern hemisphere, while the trickier astronomical definition fit reality

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<v Speaker 1>better over the oceans in the southern hemisphere. Nevertheless, the

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<v Speaker 1>astronomical definition of the seasons continues to be the one

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<v Speaker 1>generally used in the United States. Trenwerth told us after

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<v Speaker 1>my article there were a few places that tried to change,

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<v Speaker 1>but it petered out. However, climate change, largely driven by

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<v Speaker 1>human activity, has been messing with the traditional concept of

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<v Speaker 1>four seasons. Scientists have discovered that as the planet warms up,

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<v Speaker 1>the tropics have been expanding by point one to point

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<v Speaker 1>two degrees of latitude every decade. That means places that

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<v Speaker 1>once had four seasons are shifting to having just two.

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<v Speaker 1>But even in regions it's still experienced four seasons, weather

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<v Speaker 1>and temperature patterns have been altered across the United States.

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<v Speaker 1>The shift from cold winter weather to warm spring temperatures

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<v Speaker 1>happens earlier now than it did in the past, and

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<v Speaker 1>the period of into weather is shorter and generally milder.

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<v Speaker 1>In the first few months of some eastern US cities

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<v Speaker 1>were even beset by startling summer like conditions In February,

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<v Speaker 1>with many reaching or surpassing their all time temperature records.

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<v Speaker 1>Climate change induced seasonal creep, coupled with the overall warming

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<v Speaker 1>trend might make you wonder whether the concept of four

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<v Speaker 1>seasons may eventually become obsolete. Trend Birth, who is currently

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<v Speaker 1>a scientist at the National Center for Atmospheric Research and

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<v Speaker 1>who was a co recipient of the two thousand seven

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<v Speaker 1>Nobel Peace Prize for his work in climate studies, doesn't

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<v Speaker 1>see that happening, but he says the definition of the

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<v Speaker 1>seasons may change. Will still have winter, spring, summer, in

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<v Speaker 1>autumn in the middle latitudes, just the timing and duration

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<v Speaker 1>will be different, he said. A key point, though, is

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<v Speaker 1>the idea of four seasons, and the way I think

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<v Speaker 1>of it is the two extreme seasons summer and winter,

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<v Speaker 1>and to transition seasons, one could redefine the latter to

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<v Speaker 1>be shorter. In some sense, the summer is becoming longer.

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<v Speaker 1>The summer is not just temperature, but also the character

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<v Speaker 1>of the weather, more convective thunderstorms, etcetera, versus winters, more

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<v Speaker 1>extra tropical storms, cold fronts, etcetera. There's one analysis that

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<v Speaker 1>suggests summers are now thirteen days longer, and winters are

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<v Speaker 1>twenty days shorter than they used to be. Today's episode

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<v Speaker 1>was written by Patrick J. Tiger and produced by Tristan

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<v Speaker 1>McNeil and Tyler Playing. For more on this and lots

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<v Speaker 1>of other curious topics, visit how stuff works dot com.

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<v Speaker 1>Brain Stuff is production of iHeart Radio. For more podcasts

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