1 00:00:02,160 --> 00:00:04,680 Speaker 1: Welcome to brain Stuff, a production of I Heart Radio. 2 00:00:07,240 --> 00:00:09,720 Speaker 1: Hi brain Stuff, I'm Lauren vogel Bomb and this is 3 00:00:09,720 --> 00:00:13,240 Speaker 1: another classic episode from our archives. The seasons are in 4 00:00:13,240 --> 00:00:16,439 Speaker 1: the midst of changing, but they're not changing quite the 5 00:00:16,440 --> 00:00:19,079 Speaker 1: same way that they used to. Is it time to 6 00:00:19,160 --> 00:00:23,919 Speaker 1: redefine them? Hey, they're brain stuff Lauren vogel Bomb here. 7 00:00:24,239 --> 00:00:27,040 Speaker 1: If you live in Earth's middle latitudes, you're accustomed to 8 00:00:27,120 --> 00:00:31,840 Speaker 1: experiencing four traditional seasons winter, spring, summer, and autumn, also 9 00:00:31,880 --> 00:00:34,560 Speaker 1: known as fall. That means that existence in the two 10 00:00:34,600 --> 00:00:37,280 Speaker 1: bands of latitude stretching around the planet from thirty to 11 00:00:37,479 --> 00:00:40,360 Speaker 1: sixty degrees both north and south of the tropics, offers 12 00:00:40,400 --> 00:00:43,600 Speaker 1: a lot more variety weatherwise than on the equator, where 13 00:00:43,600 --> 00:00:47,200 Speaker 1: there's basically a hot, dry season and a hot, rainy season. 14 00:00:47,720 --> 00:00:50,240 Speaker 1: It's a similar story for the upper latitudes, whose residents 15 00:00:50,280 --> 00:00:52,440 Speaker 1: get a cold winter with long dark nights and a 16 00:00:52,520 --> 00:00:56,600 Speaker 1: slightly less cold summer with longer daylight. To be technical 17 00:00:56,640 --> 00:00:59,000 Speaker 1: about it, there are actually two different ways of defining 18 00:00:59,000 --> 00:01:04,080 Speaker 1: the seasons, the astronomical definition and the meteorological definition. The 19 00:01:04,160 --> 00:01:07,319 Speaker 1: astronomical definition is based upon change in the length of 20 00:01:07,400 --> 00:01:10,080 Speaker 1: days that's caused by the relative tilt of the Earth's 21 00:01:10,120 --> 00:01:13,520 Speaker 1: axis as it revolves around the Sun. So in that system, 22 00:01:13,720 --> 00:01:16,520 Speaker 1: winter is the time between the winter solstice, the shortest 23 00:01:16,520 --> 00:01:18,920 Speaker 1: period of daylight of the year, which occurs around December 24 00:01:18,959 --> 00:01:22,520 Speaker 1: twenty two, and the vernal or spring equinox, when day 25 00:01:22,520 --> 00:01:26,280 Speaker 1: and night are roughly equal, which occurs around March twenty one. 26 00:01:26,720 --> 00:01:29,880 Speaker 1: Spring then lasts from the vernal equinox to the summer solstice, 27 00:01:29,920 --> 00:01:31,959 Speaker 1: which is the longest daylight period of the year and 28 00:01:32,000 --> 00:01:35,840 Speaker 1: happens around June. Summer runs from then until the autumnal 29 00:01:35,920 --> 00:01:39,000 Speaker 1: equinox on September twenty three, another day when light and 30 00:01:39,080 --> 00:01:42,680 Speaker 1: darkness are equal. Then autumn continues until the winter solstice. 31 00:01:43,319 --> 00:01:45,920 Speaker 1: The meteorological method, on the other hand, has been around 32 00:01:46,000 --> 00:01:48,280 Speaker 1: since at least the mid nineteen hundreds and is a 33 00:01:48,280 --> 00:01:51,400 Speaker 1: lot simpler. The year is divided into four seasons by 34 00:01:51,440 --> 00:01:55,240 Speaker 1: calendar months, so that winter is December January February, spring 35 00:01:55,400 --> 00:01:58,440 Speaker 1: is March April May, summer is June July August, and 36 00:01:58,520 --> 00:02:03,280 Speaker 1: autumn is September October in November. Study conducted by climate 37 00:02:03,320 --> 00:02:07,480 Speaker 1: researcher Kevin Trenberth found that the simpler meteorological definition more 38 00:02:07,520 --> 00:02:10,760 Speaker 1: closely agreed with observable weather in the continental regions of 39 00:02:10,760 --> 00:02:14,920 Speaker 1: the northern hemisphere, while the trickier astronomical definition fit reality 40 00:02:14,960 --> 00:02:19,120 Speaker 1: better over the oceans in the southern hemisphere. Nevertheless, the 41 00:02:19,160 --> 00:02:21,919 Speaker 1: astronomical definition of the seasons continues to be the one 42 00:02:22,040 --> 00:02:25,280 Speaker 1: generally used in the United States. Trenwerth told us after 43 00:02:25,320 --> 00:02:27,880 Speaker 1: my article there were a few places that tried to change, 44 00:02:27,919 --> 00:02:31,720 Speaker 1: but it petered out. However, climate change, largely driven by 45 00:02:31,800 --> 00:02:34,640 Speaker 1: human activity, has been messing with the traditional concept of 46 00:02:34,720 --> 00:02:38,360 Speaker 1: four seasons. Scientists have discovered that as the planet warms up, 47 00:02:38,400 --> 00:02:41,200 Speaker 1: the tropics have been expanding by point one to point 48 00:02:41,200 --> 00:02:44,640 Speaker 1: two degrees of latitude every decade. That means places that 49 00:02:44,720 --> 00:02:47,400 Speaker 1: once had four seasons are shifting to having just two. 50 00:02:47,919 --> 00:02:50,760 Speaker 1: But even in regions it's still experienced four seasons, weather 51 00:02:50,840 --> 00:02:54,000 Speaker 1: and temperature patterns have been altered across the United States. 52 00:02:54,080 --> 00:02:56,920 Speaker 1: The shift from cold winter weather to warm spring temperatures 53 00:02:56,960 --> 00:02:59,200 Speaker 1: happens earlier now than it did in the past, and 54 00:02:59,240 --> 00:03:02,280 Speaker 1: the period of into weather is shorter and generally milder. 55 00:03:02,840 --> 00:03:05,919 Speaker 1: In the first few months of some eastern US cities 56 00:03:05,960 --> 00:03:09,120 Speaker 1: were even beset by startling summer like conditions In February, 57 00:03:09,440 --> 00:03:12,520 Speaker 1: with many reaching or surpassing their all time temperature records. 58 00:03:13,000 --> 00:03:16,320 Speaker 1: Climate change induced seasonal creep, coupled with the overall warming 59 00:03:16,360 --> 00:03:18,919 Speaker 1: trend might make you wonder whether the concept of four 60 00:03:18,919 --> 00:03:22,639 Speaker 1: seasons may eventually become obsolete. Trend Birth, who is currently 61 00:03:22,680 --> 00:03:25,320 Speaker 1: a scientist at the National Center for Atmospheric Research and 62 00:03:25,400 --> 00:03:27,839 Speaker 1: who was a co recipient of the two thousand seven 63 00:03:27,919 --> 00:03:30,600 Speaker 1: Nobel Peace Prize for his work in climate studies, doesn't 64 00:03:30,639 --> 00:03:33,400 Speaker 1: see that happening, but he says the definition of the 65 00:03:33,440 --> 00:03:36,560 Speaker 1: seasons may change. Will still have winter, spring, summer, in 66 00:03:36,600 --> 00:03:39,400 Speaker 1: autumn in the middle latitudes, just the timing and duration 67 00:03:39,440 --> 00:03:42,440 Speaker 1: will be different, he said. A key point, though, is 68 00:03:42,480 --> 00:03:44,600 Speaker 1: the idea of four seasons, and the way I think 69 00:03:44,600 --> 00:03:47,080 Speaker 1: of it is the two extreme seasons summer and winter, 70 00:03:47,200 --> 00:03:50,800 Speaker 1: and to transition seasons, one could redefine the latter to 71 00:03:50,880 --> 00:03:54,280 Speaker 1: be shorter. In some sense, the summer is becoming longer. 72 00:03:54,400 --> 00:03:56,920 Speaker 1: The summer is not just temperature, but also the character 73 00:03:57,000 --> 00:04:01,280 Speaker 1: of the weather, more convective thunderstorms, etcetera, versus winters, more 74 00:04:01,480 --> 00:04:05,480 Speaker 1: extra tropical storms, cold fronts, etcetera. There's one analysis that 75 00:04:05,560 --> 00:04:08,560 Speaker 1: suggests summers are now thirteen days longer, and winters are 76 00:04:08,600 --> 00:04:15,880 Speaker 1: twenty days shorter than they used to be. Today's episode 77 00:04:15,880 --> 00:04:18,120 Speaker 1: was written by Patrick J. Tiger and produced by Tristan 78 00:04:18,160 --> 00:04:20,839 Speaker 1: McNeil and Tyler Playing. For more on this and lots 79 00:04:20,839 --> 00:04:23,840 Speaker 1: of other curious topics, visit how stuff works dot com. 80 00:04:23,920 --> 00:04:26,760 Speaker 1: Brain Stuff is production of iHeart Radio. For more podcasts 81 00:04:26,760 --> 00:04:29,720 Speaker 1: from my heart Radio, visit the iHeart Radio app, Apple Podcasts, 82 00:04:29,760 --> 00:04:31,560 Speaker 1: or wherever you listen to your favorite shows.