WEBVTT 00:00:06.595 --> 00:00:08.120 To understand climate change, 00:00:08.120 --> 00:00:09.844 think of the game "Tetris." 00:00:09.844 --> 00:00:14.262 For eons, Earth has played a version of this game with blocks of carbon. 00:00:14.262 --> 00:00:17.797 They enter the atmosphere as carbon dioxide gas from volcanoes, 00:00:17.797 --> 00:00:19.343 decaying plant matter, 00:00:19.343 --> 00:00:20.510 breathing creatures 00:00:20.510 --> 00:00:21.968 and the surface of the sea. 00:00:21.968 --> 00:00:25.888 And they leave the atmosphere when they're used by plants during photosynthesis, 00:00:25.888 --> 00:00:27.512 absorbed back into the ocean, 00:00:27.512 --> 00:00:29.677 or stored in soil and sediment. 00:00:29.677 --> 00:00:32.179 This game of Tetris is called the carbon cycle, 00:00:32.179 --> 00:00:34.682 and it's the engine of life on Earth. 00:00:34.682 --> 00:00:36.761 What's the connection to climate? 00:00:36.761 --> 00:00:39.177 Well, when that carbon dioxide is in the air, 00:00:39.177 --> 00:00:40.820 waiting to be reabsorbed, 00:00:40.820 --> 00:00:42.705 it traps a portion of the sun's heat, 00:00:42.705 --> 00:00:44.844 which would otherwise escape to space. 00:00:44.844 --> 00:00:47.786 That's why carbon dioxide is called a greenhouse gas. 00:00:47.786 --> 00:00:49.579 It creates a blanket of warmth, 00:00:49.579 --> 00:00:51.261 known as the greenhouse effect, 00:00:51.261 --> 00:00:53.929 that keeps our Earth from freezing like Mars. 00:00:53.929 --> 00:00:57.793 The more carbon dioxide blocks hang out in the atmosphere waiting to be cleared, 00:00:57.793 --> 00:00:59.796 the warmer Earth becomes. 00:00:59.796 --> 00:01:01.881 Though the amount of carbon in the atmosphere 00:01:01.881 --> 00:01:05.013 has varied through ice ages and astroid impacts, 00:01:05.013 --> 00:01:09.262 over the past 8,000 years the stable climate we know took shape, 00:01:09.262 --> 00:01:12.141 allowing human civilization to thrive. 00:01:12.141 --> 00:01:14.145 But about 200 years ago, 00:01:14.145 --> 00:01:17.511 we began digging up that old carbon that had been stored in the soil. 00:01:17.511 --> 00:01:20.845 These fossil fuels, coal, oil and natural gas 00:01:20.845 --> 00:01:23.697 are made from the buried remains of plants and animals 00:01:23.697 --> 00:01:26.782 that died long before humans evolved. 00:01:26.782 --> 00:01:29.179 The energy stored inside them was able to power 00:01:29.179 --> 00:01:31.871 our factories, cars and power plants. 00:01:31.871 --> 00:01:37.042 But burning these fuels also injected new carbon blocks into Earth's Tetris game. 00:01:37.042 --> 00:01:39.845 At the same time, we cleared forests for agriculture, 00:01:39.845 --> 00:01:43.466 reducing the Earth's ability to remove the blocks. 00:01:43.466 --> 00:01:46.730 And since 1750, the amount of carbon in the atmosophere 00:01:46.730 --> 00:01:48.761 has increased by 40%, 00:01:48.761 --> 00:01:50.928 and shows no sign of slowing. 00:01:50.928 --> 00:01:53.761 Just like in Tetris, the more blocks pile up, 00:01:53.761 --> 00:01:56.736 the harder it becomes to restore stability. 00:01:56.736 --> 00:01:58.928 The extra carbon dioxide in the atmosphere 00:01:58.928 --> 00:02:00.925 accelerates the greenhouse effect 00:02:00.925 --> 00:02:03.109 by trapping more heat near the surface 00:02:03.109 --> 00:02:05.823 and causing polar ice caps to melt. 00:02:05.823 --> 00:02:09.032 And the more they melt, the less sunlight they're able to reflect, 00:02:09.032 --> 00:02:12.009 making the oceans warm even faster. 00:02:12.009 --> 00:02:15.540 Sea levels rise, coastal populations are threatened with flooding, 00:02:15.540 --> 00:02:17.841 natural ecosystems are disrupted, 00:02:17.841 --> 00:02:21.425 and the weather becomes more extreme over time. 00:02:21.425 --> 00:02:25.005 Climate change may effect different people and places in different ways. 00:02:25.005 --> 00:02:28.552 But, ultimately, it's a game that we're all stuck playing. 00:02:28.552 --> 00:02:30.053 And unlike in Tetris, 00:02:30.053 --> 00:02:32.975 we won't get a chance to start over and try again.