WEBVTT 00:00:06.367 --> 00:00:07.998 To understand climate change, 00:00:07.998 --> 00:00:09.747 think of the game Tetris. 00:00:09.747 --> 00:00:13.783 For eons Earth has played a version of this game with blocks of carbon. 00:00:13.783 --> 00:00:17.670 They enter the atmosphere as carbon dioxide gas from volcanoes, 00:00:17.670 --> 00:00:19.340 decaying plant matter, 00:00:19.340 --> 00:00:20.508 breathing creatures 00:00:20.508 --> 00:00:22.010 and the surface of the sea. 00:00:22.010 --> 00:00:25.930 And they leave the atmosphere when they're used by plants during photosynthesis, 00:00:25.930 --> 00:00:27.617 absorbed back into the ocean 00:00:27.617 --> 00:00:29.808 or stored in soil and sediment. 00:00:29.808 --> 00:00:32.185 This game of Tetris is called the carbon cycle, 00:00:32.185 --> 00:00:34.312 and it's the engine of life on Earth. 00:00:34.312 --> 00:00:36.700 What's the connection to climate? 00:00:36.700 --> 00:00:39.151 Well, when that carbon dioxide is in the air, 00:00:39.151 --> 00:00:40.904 waiting to be reabsorbed, 00:00:40.904 --> 00:00:42.783 it traps a portion of the sun's heat, 00:00:42.783 --> 00:00:44.782 which would otherwise escape to space. 00:00:44.782 --> 00:00:47.839 That's why carbon dioxide is called a greenhouse gas. 00:00:47.839 --> 00:00:49.537 It creates a blanket of warmth, 00:00:49.537 --> 00:00:51.219 known as the greenhouse effect, 00:00:51.219 --> 00:00:53.500 that keeps our Earth from freezing like Mars. 00:00:53.500 --> 00:00:57.885 The more carbon dioxide blocks hang out in the atmosphere waiting to be cleared, 00:00:57.885 --> 00:00:59.920 the warmer Earth becomes. 00:00:59.920 --> 00:01:01.883 Though the amount of carbon in the atmosphere 00:01:01.883 --> 00:01:05.010 has varied through ice ages and astroid impacts, 00:01:05.010 --> 00:01:09.385 over the past 8,000 years the stable climate we know took shape, 00:01:09.385 --> 00:01:12.218 allowing human civilization to thrive. 00:01:12.218 --> 00:01:13.967 But about 200 years ago, 00:01:13.967 --> 00:01:17.468 we began digging up that old carbon that had been stored in the soil. 00:01:17.468 --> 00:01:20.941 These fossil fuels, coal, oil and natural gas 00:01:20.941 --> 00:01:23.613 are made from the buried remains of plants and animals 00:01:23.613 --> 00:01:26.908 that died long before humans evolved. 00:01:26.908 --> 00:01:29.136 The energy stored inside them was able to power 00:01:29.136 --> 00:01:32.038 our factories, cars and power plants. 00:01:32.038 --> 00:01:37.083 But burning these fuels also injected new carbon blocks into Earth's Tetris game. 00:01:37.083 --> 00:01:40.087 At the same time, we cleared forests for agriculture, 00:01:40.087 --> 00:01:43.385 reducing the earth's ability to remove the blocks. 00:01:43.385 --> 00:01:46.719 And since 1750, the amount of carbon in the atmosophere 00:01:46.719 --> 00:01:48.718 has increased by 40%, 00:01:48.718 --> 00:01:51.385 and shows no sign of slowing. 00:01:51.385 --> 00:01:53.885 Just like in Tetris, the more blocks pile up, 00:01:53.885 --> 00:01:56.771 the harder it becomes to restore stability. 00:01:56.771 --> 00:01:58.939 The extra carbon dioxide in the atmosphere 00:01:58.939 --> 99:59:59.999 accelerates the Greenhouse Effect 99:59:59.999 --> 99:59:59.999 by trapping more heat near the surface 99:59:59.999 --> 99:59:59.999 and causing polar ice caps to melt. 99:59:59.999 --> 99:59:59.999 And the more they melt, the less sunlight they're able to reflect, 99:59:59.999 --> 99:59:59.999 making the oceans warm even faster. 99:59:59.999 --> 99:59:59.999 Sea levels rise, coastal populations are threatened with flooding, 99:59:59.999 --> 99:59:59.999 natural ecosystems are disrupted, 99:59:59.999 --> 99:59:59.999 and the weather becomes more extreme over time. 99:59:59.999 --> 99:59:59.999 Climate change may effect different people and places in different ways. 99:59:59.999 --> 99:59:59.999 But, ultimately, it's a game that we're all stuck playing. 99:59:59.999 --> 99:59:59.999 And unlike in Tetris, 99:59:59.999 --> 99:59:59.999 we won't get a chance to start over and try again.