1
00:00:00,600 --> 00:00:03,360
Speaker 1: Welcome to brain stuff front House, stuff works dot Com

2
00:00:03,680 --> 00:00:12,640
Speaker 1: where smart Happens. Hi a Marshall Brain with today's question,

3
00:00:13,080 --> 00:00:17,040
Speaker 1: how do they measure sea level? An accurate measurement of

4
00:00:17,160 --> 00:00:20,759
Speaker 1: sea level is very hard to pin down. It seems

5
00:00:20,800 --> 00:00:23,920
Speaker 1: like it would be easy, but it's actually quite complicated.

6
00:00:24,320 --> 00:00:28,480
Speaker 1: It's an important measurement though, for two reasons. First, by

7
00:00:28,560 --> 00:00:32,040
Speaker 1: having an accurate sea level measurement, it's possible to measure

8
00:00:32,040 --> 00:00:36,400
Speaker 1: the height of everything on land accurately. Second, by knowing

9
00:00:36,520 --> 00:00:39,640
Speaker 1: sea level, we can determine if the oceans are rising

10
00:00:39,760 --> 00:00:43,839
Speaker 1: or falling over time. The concern is that global warming

11
00:00:43,840 --> 00:00:47,400
Speaker 1: and other weather changes caused by man might be leading

12
00:00:47,400 --> 00:00:50,800
Speaker 1: to an overall rise in sea level. If so, coastal

13
00:00:50,880 --> 00:00:54,720
Speaker 1: cities are in big trouble. The problem with measuring the

14
00:00:54,840 --> 00:00:58,080
Speaker 1: level of the sea is that there are so many

15
00:00:58,160 --> 00:01:01,360
Speaker 1: different things that perturb it. If you could take planet

16
00:01:01,440 --> 00:01:04,120
Speaker 1: Earth and move it out into deep space so that

17
00:01:04,160 --> 00:01:07,160
Speaker 1: the Sun, the Moon, and the other planets didn't affect it,

18
00:01:07,600 --> 00:01:12,040
Speaker 1: and there were no temperature variations worldwide, then everything would

19
00:01:12,080 --> 00:01:16,199
Speaker 1: settle down like a still pond. Rain and wind would stop,

20
00:01:16,280 --> 00:01:19,160
Speaker 1: and so would the rivers. Then you could measure the

21
00:01:19,280 --> 00:01:22,600
Speaker 1: sea level accurately. If you did this, the level of

22
00:01:22,640 --> 00:01:26,320
Speaker 1: the ocean's water projected across the entire planet would be

23
00:01:26,360 --> 00:01:29,399
Speaker 1: called the g oid. On land, you can think of

24
00:01:29,440 --> 00:01:32,360
Speaker 1: the geoid as the level that ocean water would have

25
00:01:32,520 --> 00:01:34,560
Speaker 1: if you were to dig a canal from the ocean

26
00:01:34,760 --> 00:01:38,200
Speaker 1: shore to any point on land. But the Earth is

27
00:01:38,280 --> 00:01:41,080
Speaker 1: not in deep space. It's in the middle of a

28
00:01:41,200 --> 00:01:45,160
Speaker 1: chaotic solar system. There are all sorts of things changing

29
00:01:45,160 --> 00:01:48,840
Speaker 1: the water level at any given point, including the tides

30
00:01:49,000 --> 00:01:52,320
Speaker 1: which are caused by the moon, large and small waves

31
00:01:52,440 --> 00:01:56,120
Speaker 1: caused by wind and the tides, high and low pressure

32
00:01:56,160 --> 00:01:59,560
Speaker 1: areas in the atmosphere, which changed the surface level of

33
00:01:59,600 --> 00:02:02,680
Speaker 1: the ocean, and by pushing or pulling on it, temperature

34
00:02:02,760 --> 00:02:05,840
Speaker 1: changes in the ocean itself which changed the density and

35
00:02:05,960 --> 00:02:10,040
Speaker 1: volume of the ocean's water, rainfall and river water flowing

36
00:02:10,040 --> 00:02:12,600
Speaker 1: into the ocean, and so on. If you were to

37
00:02:12,720 --> 00:02:15,720
Speaker 1: stand on the ocean shore and try to measure the

38
00:02:15,800 --> 00:02:18,160
Speaker 1: sea level with a ruler, he would find it to

39
00:02:18,160 --> 00:02:22,240
Speaker 1: be impossible. The level changes by the second from the waves,

40
00:02:22,520 --> 00:02:24,920
Speaker 1: by the hour from the tides, and by the weak

41
00:02:25,320 --> 00:02:29,239
Speaker 1: from planetary and solar orbit changes. To get around all

42
00:02:29,280 --> 00:02:34,480
Speaker 1: these different variations scientists try using something called tide gauges.

43
00:02:35,160 --> 00:02:38,200
Speaker 1: A tide gauge is a large like one foot in

44
00:02:38,240 --> 00:02:42,160
Speaker 1: diameter and long like ten or twenty or thirty feet

45
00:02:42,240 --> 00:02:46,040
Speaker 1: long pipe with a small hole below the water line.

46
00:02:46,440 --> 00:02:50,720
Speaker 1: This pipe is often called a stilling well. Even though

47
00:02:50,800 --> 00:02:54,480
Speaker 1: the waves are changing the water level outside the gauge constantly,

48
00:02:54,840 --> 00:02:58,360
Speaker 1: they have little effect. Inside the gauge, the sea level

49
00:02:58,400 --> 00:03:02,240
Speaker 1: can be read relatively accurate lee inside this pipe. If

50
00:03:02,320 --> 00:03:05,200
Speaker 1: read on a regular basis over a time span of

51
00:03:05,360 --> 00:03:09,240
Speaker 1: years and then average, you can get a good measurement

52
00:03:09,280 --> 00:03:12,920
Speaker 1: of sea level. You can see that getting an accurate reading,

53
00:03:13,040 --> 00:03:16,640
Speaker 1: for example, down to the millimeter level, is extremely difficult.

54
00:03:17,040 --> 00:03:19,760
Speaker 1: Satellites are now used as well, but they suffer from

55
00:03:19,800 --> 00:03:23,160
Speaker 1: many of the same problems. Scientists do the best they can,

56
00:03:23,560 --> 00:03:27,120
Speaker 1: using extremely long time spans to try to figure out

57
00:03:27,200 --> 00:03:30,240
Speaker 1: what this sea level actually is and whether or not

58
00:03:30,400 --> 00:03:34,440
Speaker 1: it is actually rising. The general consensus seems to be

59
00:03:34,520 --> 00:03:38,360
Speaker 1: that the ocean's rise about two millimeters per year right now.

60
00:03:42,440 --> 00:03:44,480
Speaker 1: This episode of brain Stuff is brought to you by

61
00:03:44,560 --> 00:03:47,960
Speaker 1: Linda dot Com. Linda dot Com offers thousands of engaging,

62
00:03:48,000 --> 00:03:51,160
Speaker 1: easy to follow video tutorials taught by industry experts to

63
00:03:51,200 --> 00:03:54,840
Speaker 1: help you learn software, creative and business skills. Membership starts

64
00:03:54,840 --> 00:03:58,400
Speaker 1: at twenty five a month and provides unlimited seven access.

65
00:03:58,560 --> 00:04:01,200
Speaker 1: Try Linda dot com free for seven days by visiting

66
00:04:01,240 --> 00:04:03,280
Speaker 1: Linda dot com slash brainstuff