Speaker 1: Welcome to brain Stuff, a production of I Heart Radio.
Speaker 1: Hi brain Stuff, I'm Lauren vogel Bomb and this is
Speaker 1: another classic episode from our archives. The seasons are in
Speaker 1: the midst of changing, but they're not changing quite the
Speaker 1: same way that they used to. Is it time to
Speaker 1: redefine them? Hey, they're brain stuff Lauren vogel Bomb here.
Speaker 1: If you live in Earth's middle latitudes, you're accustomed to
Speaker 1: experiencing four traditional seasons winter, spring, summer, and autumn, also
Speaker 1: known as fall. That means that existence in the two
Speaker 1: bands of latitude stretching around the planet from thirty to
Speaker 1: sixty degrees both north and south of the tropics, offers
Speaker 1: a lot more variety weatherwise than on the equator, where
Speaker 1: there's basically a hot, dry season and a hot, rainy season.
Speaker 1: It's a similar story for the upper latitudes, whose residents
Speaker 1: get a cold winter with long dark nights and a
Speaker 1: slightly less cold summer with longer daylight. To be technical
Speaker 1: about it, there are actually two different ways of defining
Speaker 1: the seasons, the astronomical definition and the meteorological definition. The
Speaker 1: astronomical definition is based upon change in the length of
Speaker 1: days that's caused by the relative tilt of the Earth's
Speaker 1: axis as it revolves around the Sun. So in that system,
Speaker 1: winter is the time between the winter solstice, the shortest
Speaker 1: period of daylight of the year, which occurs around December
Speaker 1: twenty two, and the vernal or spring equinox, when day
Speaker 1: and night are roughly equal, which occurs around March twenty one.
Speaker 1: Spring then lasts from the vernal equinox to the summer solstice,
Speaker 1: which is the longest daylight period of the year and
Speaker 1: happens around June. Summer runs from then until the autumnal
Speaker 1: equinox on September twenty three, another day when light and
Speaker 1: darkness are equal. Then autumn continues until the winter solstice.
Speaker 1: The meteorological method, on the other hand, has been around
Speaker 1: since at least the mid nineteen hundreds and is a
Speaker 1: lot simpler. The year is divided into four seasons by
Speaker 1: calendar months, so that winter is December January February, spring
Speaker 1: is March April May, summer is June July August, and
Speaker 1: autumn is September October in November. Study conducted by climate
Speaker 1: researcher Kevin Trenberth found that the simpler meteorological definition more
Speaker 1: closely agreed with observable weather in the continental regions of
Speaker 1: the northern hemisphere, while the trickier astronomical definition fit reality
Speaker 1: better over the oceans in the southern hemisphere. Nevertheless, the
Speaker 1: astronomical definition of the seasons continues to be the one
Speaker 1: generally used in the United States. Trenwerth told us after
Speaker 1: my article there were a few places that tried to change,
Speaker 1: but it petered out. However, climate change, largely driven by
Speaker 1: human activity, has been messing with the traditional concept of
Speaker 1: four seasons. Scientists have discovered that as the planet warms up,
Speaker 1: the tropics have been expanding by point one to point
Speaker 1: two degrees of latitude every decade. That means places that
Speaker 1: once had four seasons are shifting to having just two.
Speaker 1: But even in regions it's still experienced four seasons, weather
Speaker 1: and temperature patterns have been altered across the United States.
Speaker 1: The shift from cold winter weather to warm spring temperatures
Speaker 1: happens earlier now than it did in the past, and
Speaker 1: the period of into weather is shorter and generally milder.
Speaker 1: In the first few months of some eastern US cities
Speaker 1: were even beset by startling summer like conditions In February,
Speaker 1: with many reaching or surpassing their all time temperature records.
Speaker 1: Climate change induced seasonal creep, coupled with the overall warming
Speaker 1: trend might make you wonder whether the concept of four
Speaker 1: seasons may eventually become obsolete. Trend Birth, who is currently
Speaker 1: a scientist at the National Center for Atmospheric Research and
Speaker 1: who was a co recipient of the two thousand seven
Speaker 1: Nobel Peace Prize for his work in climate studies, doesn't
Speaker 1: see that happening, but he says the definition of the
Speaker 1: seasons may change. Will still have winter, spring, summer, in
Speaker 1: autumn in the middle latitudes, just the timing and duration
Speaker 1: will be different, he said. A key point, though, is
Speaker 1: the idea of four seasons, and the way I think
Speaker 1: of it is the two extreme seasons summer and winter,
Speaker 1: and to transition seasons, one could redefine the latter to
Speaker 1: be shorter. In some sense, the summer is becoming longer.
Speaker 1: The summer is not just temperature, but also the character
Speaker 1: of the weather, more convective thunderstorms, etcetera, versus winters, more
Speaker 1: extra tropical storms, cold fronts, etcetera. There's one analysis that
Speaker 1: suggests summers are now thirteen days longer, and winters are
Speaker 1: twenty days shorter than they used to be. Today's episode
Speaker 1: was written by Patrick J. Tiger and produced by Tristan
Speaker 1: McNeil and Tyler Playing. For more on this and lots
Speaker 1: of other curious topics, visit how stuff works dot com.
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