1 00:00:06,595 --> 00:00:08,120 To understand climate change, 2 00:00:08,120 --> 00:00:09,844 think of the game "Tetris." 3 00:00:09,844 --> 00:00:14,262 For eons, Earth has played a version of this game with blocks of carbon. 4 00:00:14,262 --> 00:00:17,797 They enter the atmosphere as carbon dioxide gas from volcanoes, 5 00:00:17,797 --> 00:00:19,343 decaying plant matter, 6 00:00:19,343 --> 00:00:20,510 breathing creatures 7 00:00:20,510 --> 00:00:21,968 and the surface of the sea. 8 00:00:21,968 --> 00:00:25,888 And they leave the atmosphere when they're used by plants during photosynthesis, 9 00:00:25,888 --> 00:00:27,512 absorbed back into the ocean, 10 00:00:27,512 --> 00:00:29,677 or stored in soil and sediment. 11 00:00:29,677 --> 00:00:32,179 This game of Tetris is called the carbon cycle, 12 00:00:32,179 --> 00:00:34,682 and it's the engine of life on Earth. 13 00:00:34,682 --> 00:00:36,761 What's the connection to climate? 14 00:00:36,761 --> 00:00:39,177 Well, when that carbon dioxide is in the air, 15 00:00:39,177 --> 00:00:40,820 waiting to be reabsorbed, 16 00:00:40,820 --> 00:00:42,705 it traps a portion of the sun's heat, 17 00:00:42,705 --> 00:00:44,844 which would otherwise escape to space. 18 00:00:44,844 --> 00:00:47,786 That's why carbon dioxide is called a greenhouse gas. 19 00:00:47,786 --> 00:00:49,579 It creates a blanket of warmth, 20 00:00:49,579 --> 00:00:51,261 known as the greenhouse effect, 21 00:00:51,261 --> 00:00:53,929 that keeps our Earth from freezing like Mars. 22 00:00:53,929 --> 00:00:57,793 The more carbon dioxide blocks hang out in the atmosphere waiting to be cleared, 23 00:00:57,793 --> 00:00:59,796 the warmer Earth becomes. 24 00:00:59,796 --> 00:01:01,881 Though the amount of carbon in the atmosphere 25 00:01:01,881 --> 00:01:05,013 has varied through ice ages and astroid impacts, 26 00:01:05,013 --> 00:01:09,262 over the past 8,000 years the stable climate we know took shape, 27 00:01:09,262 --> 00:01:12,141 allowing human civilization to thrive. 28 00:01:12,141 --> 00:01:14,145 But about 200 years ago, 29 00:01:14,145 --> 00:01:17,511 we began digging up that old carbon that had been stored in the soil. 30 00:01:17,511 --> 00:01:20,845 These fossil fuels, coal, oil and natural gas 31 00:01:20,845 --> 00:01:23,697 are made from the buried remains of plants and animals 32 00:01:23,697 --> 00:01:26,782 that died long before humans evolved. 33 00:01:26,782 --> 00:01:29,179 The energy stored inside them was able to power 34 00:01:29,179 --> 00:01:31,871 our factories, cars and power plants. 35 00:01:31,871 --> 00:01:37,042 But burning these fuels also injected new carbon blocks into Earth's Tetris game. 36 00:01:37,042 --> 00:01:39,845 At the same time, we cleared forests for agriculture, 37 00:01:39,845 --> 00:01:43,466 reducing the Earth's ability to remove the blocks. 38 00:01:43,466 --> 00:01:46,730 And since 1750, the amount of carbon in the atmosophere 39 00:01:46,730 --> 00:01:48,761 has increased by 40%, 40 00:01:48,761 --> 00:01:50,928 and shows no sign of slowing. 41 00:01:50,928 --> 00:01:53,761 Just like in Tetris, the more blocks pile up, 42 00:01:53,761 --> 00:01:56,736 the harder it becomes to restore stability. 43 00:01:56,736 --> 00:01:58,928 The extra carbon dioxide in the atmosphere 44 00:01:58,928 --> 00:02:00,925 accelerates the greenhouse effect 45 00:02:00,925 --> 00:02:03,109 by trapping more heat near the surface 46 00:02:03,109 --> 00:02:05,823 and causing polar ice caps to melt. 47 00:02:05,823 --> 00:02:09,032 And the more they melt, the less sunlight they're able to reflect, 48 00:02:09,032 --> 00:02:12,009 making the oceans warm even faster. 49 00:02:12,009 --> 00:02:15,540 Sea levels rise, coastal populations are threatened with flooding, 50 00:02:15,540 --> 00:02:17,841 natural ecosystems are disrupted, 51 00:02:17,841 --> 00:02:21,425 and the weather becomes more extreme over time. 52 00:02:21,425 --> 00:02:25,005 Climate change may effect different people and places in different ways. 53 00:02:25,005 --> 00:02:28,552 But, ultimately, it's a game that we're all stuck playing. 54 00:02:28,552 --> 00:02:30,053 And unlike in Tetris, 55 00:02:30,053 --> 00:02:32,975 we won't get a chance to start over and try again.