1
00:00:08,170 --> 00:00:04,080
Music

2
00:00:08,190 --> 00:00:12,250
Narrator: What safeguards our solar system...

3
00:00:12,270 --> 00:00:16,320
is our star.

4
00:00:16,340 --> 00:00:20,390
The sun provides a shield, stretching beyond the last

5
00:00:20,410 --> 00:00:24,440
planet in its orbit: a force field that deflects these

6
00:00:24,460 --> 00:00:28,480
"cosmic rays." But these

7
00:00:28,500 --> 00:00:32,510
"solar winds" can be dangerous too,

8
00:00:32,530 --> 00:00:36,520
especially during outbursts called coronal mass ejections.

9
00:00:36,540 --> 00:00:40,640
Want a vision of earth gone

10
00:00:40,660 --> 00:00:44,740
wrong? Just look at what solar storms do our

11
00:00:44,760 --> 00:00:48,840
sister planet, Venus. They strip away lighter

12
00:00:48,860 --> 00:00:52,920
elements in its upper atmosphere, hydrogen, oxygen

13
00:00:52,940 --> 00:00:57,000
and the molecule they form: water.

14
00:00:57,020 --> 00:01:01,070
What's left is a witch's brew of noxious

15
00:01:01,090 --> 00:01:05,130
chemicals including thick sulfurous clouds.

16
00:01:05,150 --> 00:01:09,180
How has Earth avoided the grim fate of Venus?

17
00:01:09,200 --> 00:01:13,220
We can see the answer as the solar storm

18
00:01:13,240 --> 00:01:17,240
approaches Earth.

19
00:01:17,260 --> 00:01:21,250
Music

20
00:01:21,270 --> 00:01:25,360
Our planet has a protective shield

21
00:01:25,380 --> 00:01:29,470
all it's own-- A powerful magnetic field

22
00:01:29,490 --> 00:01:33,560
generated deep within its core.

23
00:01:33,580 --> 00:01:37,650
In fact, that's just our first line of

24
00:01:37,670 --> 00:01:41,720
defense. Much of the solar energy that gets through

25
00:01:41,740 --> 00:01:45,790
is reflected back to space by clouds, ice,

26
00:01:45,810 --> 00:01:49,840
and snow. The energy that Earth absorbs

27
00:01:49,860 --> 00:01:53,880
is just enough to power a remarkable planetary

28
00:01:53,900 --> 00:01:57,900
engine: the climate.

29
00:01:57,920 --> 00:02:01,910
It's set in motion

30
00:02:01,930 --> 00:02:05,990
by the unevenness of solar heating, due in part to the

31
00:02:06,010 --> 00:02:10,070
cycles of day and night, and the seasons that cause warm

32
00:02:10,090 --> 00:02:14,140
tropical winds to blow toward the poles and cold

33
00:02:14,160 --> 00:02:18,200
polar air toward the equator.

34
00:02:18,220 --> 00:02:22,260
Wind currents

35
00:02:22,280 --> 00:02:26,300
drive surface ocean currents.

36
00:02:26,320 --> 00:02:30,340
This computer simulation shows the

37
00:02:30,360 --> 00:02:34,370
Gulf Stream winding its way along the coast of North America.

38
00:02:46,480 --> 00:02:38,390
Music

39
00:02:46,500 --> 00:02:50,550
This great ocean river carries enough heat energy

40
00:02:50,570 --> 00:02:54,620
to power the industrial world a hundred times

41
00:02:54,640 --> 00:02:58,670
over. It breaks down

42
00:02:58,690 --> 00:03:02,720
in massive world pools that spread warm tropical

43
00:03:02,740 --> 00:03:06,770
waters over northern seas.

44
00:03:06,790 --> 00:03:10,800
Music

45
00:03:10,820 --> 00:03:14,820
Below the surface they mix

46
00:03:14,840 --> 00:03:18,840
with cold deep currents that swirl around

47
00:03:18,860 --> 00:03:22,930
under sea ledges and mountains.

48
00:03:43,280 --> 00:03:27,020
Music

49
00:03:43,300 --> 00:03:47,330
Earth's climate engine has countless moving parts:

50
00:03:47,350 --> 00:03:51,360
tides and terrain, cross winds and currents--