1 00:00:05,384 --> 00:00:08,520 Once there was a world 2 00:00:08,554 --> 00:00:11,823 not so very different from our own. 3 00:00:18,097 --> 00:00:21,232 There were occasional natural catastrophes, 4 00:00:21,267 --> 00:00:23,535 massive volcanic eruptions 5 00:00:23,569 --> 00:00:26,705 and, every once in a while, an asteroid would come 6 00:00:26,739 --> 00:00:29,474 barreling out of the blue to do some damage. 7 00:00:29,508 --> 00:00:33,545 But for the first billion years or so, 8 00:00:33,579 --> 00:00:37,315 it would've seemed like a paradise. 9 00:00:37,350 --> 00:00:39,751 This is what we think the planet Venus 10 00:00:39,785 --> 00:00:44,155 might have looked like when our solar system was young. 11 00:00:44,190 --> 00:00:48,193 Then things started to go horribly wrong. 12 00:02:33,136 --> 00:02:34,636 "The World Set Free" 13 00:02:50,183 --> 00:02:52,617 The planet Venus, 14 00:02:52,652 --> 00:02:54,486 which once may have seemed like a heaven, 15 00:02:54,520 --> 00:02:56,621 turned into a kind of hell. 16 00:02:56,656 --> 00:02:59,724 The difference between the two can be a delicate balance, 17 00:02:59,759 --> 00:03:02,360 far more delicate than you might imagine. 18 00:03:02,395 --> 00:03:07,232 Once things began to unravel, there was no way back. 19 00:03:07,266 --> 00:03:10,468 This is what Venus, our nearest planetary neighbor, 20 00:03:10,503 --> 00:03:12,037 looks like today. 21 00:03:22,348 --> 00:03:25,584 Venus's oceans are long gone. 22 00:03:25,618 --> 00:03:28,587 The surface is hotter than a broiling oven, 23 00:03:28,621 --> 00:03:31,156 hot enough to melt lead. 24 00:03:31,190 --> 00:03:33,492 Why? You might think it's because Venus 25 00:03:33,526 --> 00:03:36,495 is 30% closer to the Sun than the Earth is, 26 00:03:36,529 --> 00:03:38,396 but that's not the reason. 27 00:03:38,431 --> 00:03:40,031 Venus is completely 28 00:03:40,066 --> 00:03:43,168 covered by clouds of sulfuric acid that keep 29 00:03:43,202 --> 00:03:46,104 almost all the sunlight from reaching the surface. 30 00:03:46,138 --> 00:03:49,107 That ought to make Venus much colder than the Earth. 31 00:03:49,141 --> 00:03:52,043 So why is Venus scorching hot? 32 00:03:52,078 --> 00:03:54,179 It's because the small amount of sunlight 33 00:03:54,213 --> 00:03:57,249 that trickles in through the clouds to reach the surface 34 00:03:57,283 --> 00:03:59,384 can't get back out again. 35 00:03:59,418 --> 00:04:02,254 The flow of energy is blocked by a dense atmosphere 36 00:04:02,288 --> 00:04:03,922 of carbon dioxide. 37 00:04:03,956 --> 00:04:07,893 That carbon dioxide gas-- or CO2 for short-- 38 00:04:07,927 --> 00:04:11,229 acts like a smothering blanket to keep the heat in. 39 00:04:11,264 --> 00:04:13,031 No one is burning coal 40 00:04:13,065 --> 00:04:15,700 or driving big gas-guzzlers on Venus. 41 00:04:15,735 --> 00:04:17,569 Nature can destroy an environment 42 00:04:17,603 --> 00:04:20,305 without any help from intelligent life. 43 00:04:20,339 --> 00:04:24,910 Venus is in the grip of a runaway greenhouse effect. 44 00:04:24,944 --> 00:04:28,814 Why does it look like we're inside a bowl? 45 00:04:28,848 --> 00:04:32,083 It's due to the intense atmospheric pressure. 46 00:04:33,786 --> 00:04:36,655 That's the wreck of Venera 13. 47 00:04:36,689 --> 00:04:39,391 In 1982, the scientists and engineers 48 00:04:39,425 --> 00:04:41,793 of what was then the Soviet Union 49 00:04:41,828 --> 00:04:44,596 successfully landed this spacecraft on Venus. 50 00:04:44,630 --> 00:04:46,832 They managed to keep it refrigerated 51 00:04:46,866 --> 00:04:48,567 for over two hours, 52 00:04:48,601 --> 00:04:51,503 so it could photograph its surroundings... 53 00:04:51,537 --> 00:04:55,006 and transmit the images back to Earth 54 00:04:55,041 --> 00:04:58,677 before the onboard electronics were fried. 55 00:05:05,184 --> 00:05:07,619 Venus and Earth started out with about the same amount 56 00:05:07,653 --> 00:05:10,422 of carbon, but the two worlds were propelled 57 00:05:10,456 --> 00:05:12,791 along radically different paths, 58 00:05:12,825 --> 00:05:16,294 and carbon was the decisive element in both stories. 59 00:05:16,329 --> 00:05:20,365 On Venus, it's almost all in the form of gas-- 60 00:05:20,399 --> 00:05:23,802 carbon dioxide-- in the atmosphere. 61 00:05:27,742 --> 00:05:30,711 Most of the carbon on Earth has been stored for eons 62 00:05:30,745 --> 00:05:33,480 in solid vaults of carbonate rock, 63 00:05:33,515 --> 00:05:35,983 like this one, part of a chain that forms 64 00:05:36,017 --> 00:05:38,752 the celebrated White Cliffs of Dover, 65 00:05:38,786 --> 00:05:41,088 right on the English Channel. 66 00:05:41,122 --> 00:05:44,691 What titan built this wonder of the world? 67 00:06:00,311 --> 00:06:04,781 A creature a thousand times smaller than a pinhead. 68 00:06:04,816 --> 00:06:06,783 Trillions of them. 69 00:06:06,818 --> 00:06:09,252 One-celled algae. 70 00:06:14,125 --> 00:06:17,461 Volcanoes supply carbon dioxide to the atmosphere, 71 00:06:17,495 --> 00:06:20,664 and the oceans slowly absorb it. 72 00:06:20,698 --> 00:06:23,333 Working over the course of millions of years, 73 00:06:23,368 --> 00:06:26,503 the microscopic algae harvested the carbon dioxide 74 00:06:26,537 --> 00:06:29,239 and turned it into these tiny shells. 75 00:06:29,273 --> 00:06:31,775 They accumulated in thick deposits of chalk, 76 00:06:31,809 --> 00:06:35,012 or limestone, on the ocean floor. 77 00:06:38,483 --> 00:06:41,852 Later, the restless Earth pushed up the seafloor 78 00:06:41,886 --> 00:06:46,189 and carved out these massive cliffs. 79 00:06:46,224 --> 00:06:48,325 Other marine creatures 80 00:06:48,359 --> 00:06:52,129 took in carbon dioxide to build enormous coral reefs. 81 00:06:52,163 --> 00:06:56,099 And the oceans converted dissolved CO2 into limestone 82 00:06:56,134 --> 00:06:58,168 even without any help from life. 83 00:06:58,202 --> 00:07:01,805 As a result, only a trace amount was left as a gas 84 00:07:01,839 --> 00:07:03,340 in Earth's atmosphere. 85 00:07:03,374 --> 00:07:06,476 Not even three-hundredths of one percent. 86 00:07:06,511 --> 00:07:09,479 Think of it-- fewer than three molecules 87 00:07:09,514 --> 00:07:12,549 out of every ten thousand. 88 00:07:15,653 --> 00:07:18,055 And yet, it makes the critical difference 89 00:07:18,089 --> 00:07:22,659 between a barren wasteland and a garden of life on Earth. 90 00:07:24,228 --> 00:07:26,163 With no CO2 at all, 91 00:07:26,197 --> 00:07:30,000 the Earth would be frozen. 92 00:07:30,034 --> 00:07:32,035 And with twice as many, 93 00:07:32,070 --> 00:07:34,004 we're still talking about only six molecules 94 00:07:34,038 --> 00:07:35,639 out of ten thousand. 95 00:07:35,673 --> 00:07:37,741 Things would get uncomfortably hot 96 00:07:37,775 --> 00:07:40,626 and cause us some serious problems... 97 00:07:40,646 --> 00:07:44,348 but never as hot as Venus; not even close. 98 00:07:44,383 --> 00:07:47,051 That planet lost its ocean to space 99 00:07:47,085 --> 00:07:48,382 billions of years ago. 100 00:07:48,421 --> 00:07:51,623 Without an ocean, it had no way to capture CO2 101 00:07:51,657 --> 00:07:54,348 from the atmosphere and store it as a mineral. 102 00:07:54,383 --> 00:07:56,496 The CO2 from erupting volcanoes 103 00:07:56,530 --> 00:07:59,165 just continued to build up. 104 00:07:59,200 --> 00:08:02,653 Today, that atmosphere is 90 times heavier than ours. 105 00:08:02,604 --> 00:08:05,921 Almost all of it is heat-trapping carbon dioxide. 106 00:08:05,975 --> 00:08:09,311 That's why Venus is such a ferocious inferno 107 00:08:09,345 --> 00:08:12,948 so hostile to life. 108 00:08:12,982 --> 00:08:16,118 The Earth, in stunning contrast, 109 00:08:16,152 --> 00:08:17,820 is alive. 110 00:08:17,854 --> 00:08:20,422 It breathes... 111 00:08:20,456 --> 00:08:22,658 but very slowly. 112 00:08:22,692 --> 00:08:24,993 A single breath takes a whole year. 113 00:08:25,028 --> 00:08:27,296 The forests contain most of Earth's life, 114 00:08:27,330 --> 00:08:30,199 and most forests are in the Northern Hemisphere. 115 00:08:30,233 --> 00:08:32,367 When spring comes to the north, 116 00:08:32,402 --> 00:08:35,437 the forests inhale carbon dioxide from the air 117 00:08:35,471 --> 00:08:38,640 and grow, turning the land green. 118 00:08:38,675 --> 00:08:41,710 The amount of CO2 in the atmosphere goes down. 119 00:08:41,744 --> 00:08:46,281 When fall comes and the plants drop their leaves, they decay, 120 00:08:46,316 --> 00:08:50,219 exhaling the carbon dioxide back into the atmosphere. 121 00:08:50,253 --> 00:08:52,855 The same thing happens in the Southern Hemisphere 122 00:08:52,889 --> 00:08:55,190 at the opposite time of the year. 123 00:08:55,225 --> 00:08:58,193 But the Southern Hemisphere is mostly ocean. 124 00:08:58,228 --> 00:09:00,229 So it's the forests of the north 125 00:09:00,263 --> 00:09:03,732 that control the annual changes in the global CO2. 126 00:09:03,766 --> 00:09:05,534 The Earth has been breathing like this 127 00:09:05,568 --> 00:09:07,146 for tens of millions of years. 128 00:09:07,704 --> 00:09:10,640 But nobody noticed until 1958, 129 00:09:10,674 --> 00:09:13,509 when an oceanographer named Charles David Keeling 130 00:09:13,543 --> 00:09:15,811 devised a way to accurately measure 131 00:09:15,846 --> 00:09:19,048 the amount of carbon dioxide in the atmosphere. 132 00:09:19,082 --> 00:09:22,885 Keeling discovered the Earth's exquisite respiration. 133 00:09:25,224 --> 00:09:27,725 But he also discovered something shocking-- 134 00:09:27,760 --> 00:09:31,396 a rapid rise, unprecedented in human history, 135 00:09:31,430 --> 00:09:33,965 in the overall level of CO2, 136 00:09:33,999 --> 00:09:36,401 one that has continued ever since. 137 00:09:42,842 --> 00:09:46,344 It's a striking departure from the CO2 levels that prevailed 138 00:09:46,378 --> 00:09:49,647 during the rise of agriculture and civilization. 139 00:09:49,682 --> 00:09:53,218 In fact, the Earth has seen nothing like it 140 00:09:53,252 --> 00:09:56,688 for three million years. 141 00:09:56,722 --> 00:09:59,591 How can we be so sure? 142 00:09:59,625 --> 00:10:03,595 The evidence is written in water. 143 00:10:11,775 --> 00:10:14,711 The Earth keeps a detailed diary 144 00:10:14,745 --> 00:10:17,046 written in the snows of yesteryear. 145 00:10:17,081 --> 00:10:19,727 Climate scientists have drilled ice cores 146 00:10:19,762 --> 00:10:22,863 from the depths of glaciers in Greenland and Antarctica. 147 00:10:23,400 --> 00:10:27,937 The ice layers have ancient air trapped inside them. 148 00:10:29,906 --> 00:10:32,475 We can read the unbroken record of Earth's atmosphere 149 00:10:32,509 --> 00:10:35,945 that extends back over the last 800,000 years. 150 00:10:35,979 --> 00:10:38,214 In all that time, 151 00:10:38,248 --> 00:10:40,816 the amount of carbon dioxide in the air never rose 152 00:10:40,851 --> 00:10:43,119 above three-hundredths of one percent. 153 00:10:43,153 --> 00:10:46,889 That is, until the turn of the 20th century. 154 00:10:46,923 --> 00:10:50,092 And it's been going up steadily and rapidly ever since. 155 00:10:50,127 --> 00:10:52,628 It's now more than 40% higher 156 00:10:52,662 --> 00:10:54,897 than before the Industrial Revolution. 157 00:10:54,931 --> 00:10:58,100 By burning coal, oil and gas, 158 00:10:58,135 --> 00:11:01,437 our civilization is exhaling carbon dioxide 159 00:11:01,471 --> 00:11:03,739 much faster than Earth can absorb it. 160 00:11:03,774 --> 00:11:07,243 So CO2 is building up in the atmosphere. 161 00:11:07,277 --> 00:11:09,478 The planet is heating up. 162 00:11:09,513 --> 00:11:12,581 Every warm object radiates a kind of light 163 00:11:12,616 --> 00:11:14,583 we can't see with the naked eye-- 164 00:11:14,618 --> 00:11:16,485 thermal infrared light. 165 00:11:16,520 --> 00:11:21,023 We all glow with invisible heat radiation, even in the dark. 166 00:11:21,058 --> 00:11:24,960 This is what the Earth looks like in the infrared. 167 00:11:24,995 --> 00:11:29,832 You're seeing the planet's own body heat. 168 00:11:34,805 --> 00:11:37,506 Incoming light from the Sun hits the surface. 169 00:11:37,541 --> 00:11:39,942 The Earth absorbs much of that energy, 170 00:11:39,977 --> 00:11:41,711 which heats the planet up 171 00:11:41,745 --> 00:11:45,781 and makes the surface glow in infrared light. 172 00:11:45,816 --> 00:11:48,184 But the carbon dioxide in the atmosphere 173 00:11:48,218 --> 00:11:51,053 absorbs most of that outgoing heat radiation, 174 00:11:51,088 --> 00:11:53,856 sending much of it right back to the surface. 175 00:11:53,890 --> 00:11:56,959 This makes the planet even warmer. 176 00:11:56,994 --> 00:11:59,295 That's all there is to the greenhouse effect. 177 00:11:59,329 --> 00:12:00,963 It's basic physics, 178 00:12:00,998 --> 00:12:03,366 just bookkeeping of the energy flow. 179 00:12:03,400 --> 00:12:06,068 There's nothing controversial about it. 180 00:12:06,103 --> 00:12:08,971 If we didn't have any carbon dioxide in our atmosphere, 181 00:12:09,006 --> 00:12:12,141 the Earth would just be a great big snowball, 182 00:12:12,175 --> 00:12:14,677 and we wouldn't be here. 183 00:12:16,780 --> 00:12:19,515 So, a little greenhouse effect is a good thing. 184 00:12:19,550 --> 00:12:22,618 But a big one can destabilize the climate 185 00:12:22,653 --> 00:12:24,754 and wreck our way of life. 186 00:12:24,788 --> 00:12:28,858 All right... but how do we know that we're the problem? 187 00:12:28,892 --> 00:12:32,695 Maybe the Earth itself is causing the rise in CO2. 188 00:12:32,730 --> 00:12:36,099 Maybe it has nothing to do with the coal and oil we burn. 189 00:12:36,133 --> 00:12:38,701 Maybe it's those damn volcanoes. 190 00:12:40,471 --> 00:12:44,707 Every few years, Mount Etna, in Sicily, blows its stack. 191 00:12:44,742 --> 00:12:48,578 Each big eruption sends millions of tons of CO2 192 00:12:48,612 --> 00:12:50,480 into the atmosphere. 193 00:12:50,514 --> 00:12:52,982 Now, combine that with the output 194 00:12:53,017 --> 00:12:56,319 of all the other volcanic activity on the planet. 195 00:12:56,353 --> 00:12:59,489 Let's take the largest scientific estimate-- 196 00:12:59,523 --> 00:13:03,326 about 500 million tons of volcanic CO2 197 00:13:03,360 --> 00:13:05,495 entering the atmosphere ever year. 198 00:13:05,529 --> 00:13:08,264 Sounds like a lot, right? 199 00:13:08,299 --> 00:13:12,802 But that's not even two percent of the 30 billion tons of CO2 200 00:13:12,836 --> 00:13:15,838 that our civilization is cranking out every year. 201 00:13:15,873 --> 00:13:17,740 And, funny thing, 202 00:13:17,775 --> 00:13:21,611 the measured increase in CO2 in the atmosphere 203 00:13:21,645 --> 00:13:25,481 tallies with the known amount we're dumping there 204 00:13:25,516 --> 00:13:29,485 by burning coal, oil and gas. 205 00:13:29,520 --> 00:13:32,588 Volcanic CO2 has a distinct signature-- 206 00:13:32,623 --> 00:13:34,257 it's slightly heavier than the kind produced 207 00:13:34,291 --> 00:13:36,659 by burning fossil fuels. 208 00:13:36,694 --> 00:13:38,528 We can tell the difference between the two 209 00:13:38,562 --> 00:13:41,164 when we examine them at the atomic level. 210 00:13:41,198 --> 00:13:43,766 It's clear that the increased CO2 in the air 211 00:13:43,801 --> 00:13:46,035 is not from volcanoes. 212 00:13:46,070 --> 00:13:49,372 What's more, the observed warming is as much as predicted 213 00:13:49,406 --> 00:13:51,507 from the measured increase in carbon dioxide. 214 00:13:51,542 --> 00:13:53,443 It's a pretty tight case. 215 00:13:53,477 --> 00:13:55,979 Our fingerprints are all over this one. 216 00:13:56,013 --> 00:14:00,383 How much is 30 billion tons of CO2 per year? 217 00:14:00,417 --> 00:14:02,852 If you compressed it into solid form, 218 00:14:02,886 --> 00:14:04,988 it would occupy about the same volume 219 00:14:05,022 --> 00:14:07,357 as the White Cliffs of Dover. 220 00:14:07,391 --> 00:14:11,794 And we're adding that much CO2 to the air every year, 221 00:14:11,829 --> 00:14:14,364 relentlessly, year after year. 222 00:14:14,398 --> 00:14:17,567 Unlucky for us, the main waste product 223 00:14:17,601 --> 00:14:21,004 of our civilization is not just any substance. 224 00:14:21,038 --> 00:14:24,540 It happens to be the chief climate-regulating gas 225 00:14:24,575 --> 00:14:27,487 of our global thermostat, year in, year out. 226 00:14:29,281 --> 00:14:31,616 Too bad CO2 is an invisible gas. 227 00:14:31,650 --> 00:14:33,784 Maybe if we could see it... 228 00:14:35,287 --> 00:14:37,455 If our eyes were sensitive to CO2-- 229 00:14:37,489 --> 00:14:40,458 and perhaps there are such beings in the cosmos-- 230 00:14:40,492 --> 00:14:43,928 if we could see all that carbon dioxide, 231 00:14:43,962 --> 00:14:46,964 then we would overcome the denial 232 00:14:46,999 --> 00:14:50,568 and grasp the magnitude of our impact on the atmosphere. 233 00:15:05,819 --> 00:15:08,020 But the evidence that the world is getting warmer 234 00:15:08,055 --> 00:15:09,956 is all around us. 235 00:15:09,990 --> 00:15:13,059 For starters, let's just check the thermometers. 236 00:15:13,093 --> 00:15:15,061 Weather stations around the world 237 00:15:15,095 --> 00:15:17,029 have been keeping reliable temperature records 238 00:15:17,064 --> 00:15:18,731 since the 1880s, 239 00:15:18,765 --> 00:15:21,867 and NASA has used the data to compile a map 240 00:15:21,902 --> 00:15:23,569 tracking the average temperatures 241 00:15:23,604 --> 00:15:25,571 around the world through time. 242 00:15:26,974 --> 00:15:28,641 Yellow means warmer temperatures 243 00:15:28,675 --> 00:15:32,645 than the average, for any region in the 1880s. 244 00:15:32,679 --> 00:15:35,915 Orange means hot. 245 00:15:37,417 --> 00:15:40,720 And red means hotter. 246 00:15:40,754 --> 00:15:43,923 The world is warmer than it was in the 19th century. 247 00:15:46,994 --> 00:15:51,664 Back then, at the greatest fair the world has ever seen, 248 00:15:51,698 --> 00:15:56,302 a forgotten genius demonstrated the solution to this problem. 249 00:15:56,336 --> 00:15:57,770 Come with me. 250 00:16:05,263 --> 00:16:07,177 Once there was a world 251 00:16:07,212 --> 00:16:10,013 that was not too hot and not too cold. 252 00:16:10,047 --> 00:16:12,515 It was just right. 253 00:16:12,620 --> 00:16:16,223 Then there came a time when the life it sustained 254 00:16:16,257 --> 00:16:20,594 began to notice our lovely planet was changing. 255 00:16:20,628 --> 00:16:25,298 And it's not as if we didn't see it coming. 256 00:16:27,903 --> 00:16:31,039 As far back as 1896, 257 00:16:31,073 --> 00:16:33,942 the Swedish scientist Svante Arrhenius 258 00:16:33,976 --> 00:16:36,344 calculated that doubling the amount 259 00:16:36,378 --> 00:16:40,148 of CO2 in the atmosphere would melt the Arctic ice. 260 00:16:42,551 --> 00:16:46,087 In the 1930s, the American physicist EO Hulburt, 261 00:16:46,121 --> 00:16:48,022 at the Naval Research Laboratory, 262 00:16:48,057 --> 00:16:49,857 confirmed that result. 263 00:16:49,892 --> 00:16:52,794 So far, it was still just theoretical. 264 00:16:55,097 --> 00:16:58,299 But then, the English engineer Guy Callendar 265 00:16:58,334 --> 00:17:00,435 assembled the evidence to show 266 00:17:00,469 --> 00:17:03,705 that both the CO2 and the average global temperature 267 00:17:03,739 --> 00:17:06,207 were actually increasing. 268 00:17:06,242 --> 00:17:10,578 Even now, man may be unwittingly changing the world's climate 269 00:17:10,613 --> 00:17:12,881 through the waste products of his civilization. 270 00:17:12,915 --> 00:17:14,883 Due to our release, through factories 271 00:17:14,917 --> 00:17:17,585 and automobiles every year, of more than 272 00:17:17,620 --> 00:17:19,888 six billion tons of carbon dioxide, 273 00:17:19,922 --> 00:17:22,323 which helps air absorb heat from the Sun, 274 00:17:22,358 --> 00:17:25,093 our atmosphere seems to be getting warmer. 275 00:17:25,127 --> 00:17:26,961 This is bad? 276 00:17:26,996 --> 00:17:29,664 Well, it's been calculated, a few degrees rise 277 00:17:29,698 --> 00:17:30,965 in the Earth's temperature 278 00:17:31,000 --> 00:17:33,768 would melt the polar ice caps. 279 00:17:38,807 --> 00:17:42,644 In 1960, Carl Sagan's PhD thesis 280 00:17:42,678 --> 00:17:44,512 included the first calculation 281 00:17:44,547 --> 00:17:47,148 of the runaway greenhouse effect on Venus. 282 00:17:47,183 --> 00:17:49,017 This was part of a career-long interest 283 00:17:49,051 --> 00:17:52,153 in the atmospheres of the planets, including our own. 284 00:17:52,188 --> 00:17:56,324 In the original Cosmos series, in 1980, Carl Sagan warned... 285 00:17:56,358 --> 00:17:58,660 We are releasing vast quantities of carbon dioxide, 286 00:17:58,694 --> 00:18:01,529 increasing the greenhouse effect. 287 00:18:01,564 --> 00:18:03,264 It may not take much 288 00:18:03,299 --> 00:18:05,667 to destabilize the Earth's climate, 289 00:18:05,701 --> 00:18:09,137 to convert this heaven, our only home in the cosmos, 290 00:18:09,171 --> 00:18:11,172 into a kind of hell. 291 00:18:16,446 --> 00:18:18,648 Since Carl spoke those words, 292 00:18:18,682 --> 00:18:21,751 we've burdened the atmosphere of our world with an additional 293 00:18:21,785 --> 00:18:26,255 400 billion tons of carbon dioxide. 294 00:18:26,290 --> 00:18:28,157 If we don't change our ways, 295 00:18:28,191 --> 00:18:30,927 what will the planet be like in our children's future? 296 00:18:30,961 --> 00:18:34,263 Based on scientific projections, 297 00:18:34,298 --> 00:18:37,133 if we just keep on doing business as usual, 298 00:18:37,167 --> 00:18:39,535 our kids are in for a rough ride. 299 00:18:39,569 --> 00:18:42,672 Killer heat waves, record droughts, 300 00:18:42,706 --> 00:18:46,509 rising sea levels, mass extinction of species. 301 00:18:46,543 --> 00:18:49,011 We inherited a bountiful world 302 00:18:49,046 --> 00:18:52,181 made possible by a relatively stable climate. 303 00:18:52,215 --> 00:18:54,550 Agriculture and civilization flourished 304 00:18:54,584 --> 00:18:56,519 for thousands of years. 305 00:18:56,553 --> 00:19:02,758 And now, our carelessness and greed put all of that at risk. 306 00:19:04,227 --> 00:19:06,395 Okay, so if we scientists are so good 307 00:19:06,430 --> 00:19:09,398 at making these dire, long-term predictions about the climate, 308 00:19:09,433 --> 00:19:12,301 how come we're so lousy about predicting the weather? 309 00:19:12,336 --> 00:19:16,172 Besides, this year, we had a colder winter in my town. 310 00:19:16,206 --> 00:19:18,140 For all us scientists know, 311 00:19:18,175 --> 00:19:20,042 we could be in for global cooling. 312 00:19:20,077 --> 00:19:22,979 Here's the difference between weather and climate... 313 00:19:23,013 --> 00:19:26,215 Weather is what the atmosphere does in the short term-- 314 00:19:26,250 --> 00:19:28,351 hour to hour, day to day. 315 00:19:28,385 --> 00:19:31,020 Weather is chaotic, which means that even 316 00:19:31,054 --> 00:19:34,023 a microscopic disturbance can lead to large-scale changes. 317 00:19:34,057 --> 00:19:36,892 That's why those ten-day weather forecasts are useless. 318 00:19:36,927 --> 00:19:41,397 A butterfly flaps its wings in Bali, and six weeks later, 319 00:19:41,431 --> 00:19:44,033 your outdoor wedding in Maine is ruined. 320 00:19:44,067 --> 00:19:46,035 Climate is the long-term average 321 00:19:46,069 --> 00:19:48,237 of the weather, over a number of years. 322 00:19:48,272 --> 00:19:50,873 It's shaped by global forces that alter the energy balance 323 00:19:50,908 --> 00:19:53,943 in the atmosphere, such as changes in the Sun, 324 00:19:53,977 --> 00:19:55,611 the tilt of the Earth's axis, 325 00:19:55,646 --> 00:19:58,414 the amount of sunlight the Earth reflects back to space 326 00:19:58,448 --> 00:20:01,684 and the concentration of greenhouse gases in the air. 327 00:20:01,718 --> 00:20:04,020 A change in any of them affects the climate 328 00:20:04,054 --> 00:20:06,622 in ways that are broadly predictable. 329 00:20:06,657 --> 00:20:08,591 My friend's meandering 330 00:20:08,625 --> 00:20:10,726 represents the short-term fluctuations-- 331 00:20:10,761 --> 00:20:13,362 that's weather. 332 00:20:13,397 --> 00:20:14,931 It's almost impossible to predict 333 00:20:14,965 --> 00:20:16,766 what'll attract his interest next, 334 00:20:16,800 --> 00:20:19,869 but not hard to know what the range of his meandering will be, 335 00:20:19,903 --> 00:20:22,638 because I'm holding him on a leash. 336 00:20:24,341 --> 00:20:26,809 We can't observe climate directly-- 337 00:20:26,843 --> 00:20:28,644 all we see is the weather-- 338 00:20:28,679 --> 00:20:30,646 but the average weather, over the course of years, 339 00:20:30,681 --> 00:20:32,315 reveals a pattern. 340 00:20:32,349 --> 00:20:34,750 I represent that long-term trend, 341 00:20:34,785 --> 00:20:36,919 which is climate. 342 00:20:36,954 --> 00:20:40,823 Keep your eye on the man, not the dog. 343 00:20:43,493 --> 00:20:45,795 Weather is hard to predict, like my friend here, 344 00:20:45,829 --> 00:20:48,397 but climate is predictable. 345 00:20:48,432 --> 00:20:51,467 Climate has changed many times in the long history of the Earth 346 00:20:51,501 --> 00:20:54,136 but always in response to a global force. 347 00:20:54,171 --> 00:20:57,473 The strongest force driving climate change right now 348 00:20:57,507 --> 00:21:00,476 is the increasing CO2 from the burning of fossil fuels, 349 00:21:00,510 --> 00:21:02,812 which is trapping more heat from the Sun. 350 00:21:02,846 --> 00:21:05,648 All that additional energy has to go somewhere. 351 00:21:05,682 --> 00:21:07,483 Some of it warms the air. 352 00:21:07,517 --> 00:21:09,585 Most of it ends up in the oceans. 353 00:21:09,620 --> 00:21:13,856 All over the world, the oceans are getting warmer. 354 00:21:13,891 --> 00:21:16,292 It's most obvious in the Arctic Ocean 355 00:21:16,326 --> 00:21:19,195 and the lands that surround it. 356 00:21:21,798 --> 00:21:24,767 Okay, so we're losing the summer sea ice 357 00:21:24,801 --> 00:21:28,371 in a place where hardly anyone ever goes. 358 00:21:28,405 --> 00:21:32,008 What do I care if there's no ice around the North Pole? 359 00:21:41,151 --> 00:21:44,120 Ice is the brightest natural surface on the Earth, 360 00:21:44,154 --> 00:21:47,056 and open ocean water is the darkest. 361 00:21:47,090 --> 00:21:50,660 Ice reflects incoming sunlight back to space. 362 00:21:50,694 --> 00:21:52,728 Water absorbs sunlight 363 00:21:52,763 --> 00:21:56,065 and gets warmer, which melts even more ice, 364 00:21:56,099 --> 00:21:59,335 which exposes still more ocean surface 365 00:21:59,369 --> 00:22:01,337 to absorb even more sunlight. 366 00:22:01,371 --> 00:22:04,807 This is what we call a positive feedback loop. 367 00:22:04,842 --> 00:22:08,578 It's one of many natural mechanisms that magnify 368 00:22:08,612 --> 00:22:11,714 any warming caused by CO2 alone. 369 00:22:11,748 --> 00:22:13,983 We're at Drew Point, Alaska, 370 00:22:14,017 --> 00:22:18,921 on the edge of the Arctic Ocean. 371 00:22:29,037 --> 00:22:32,906 When I was born, the shoreline was a mile farther out, 372 00:22:32,941 --> 00:22:36,944 and it was breaking off at a rate of about 20 feet per year. 373 00:22:36,978 --> 00:22:38,946 Now... 374 00:22:38,980 --> 00:22:43,117 it's being eaten away at about 50 feet per year. 375 00:22:43,151 --> 00:22:45,119 The Arctic Ocean is warming 376 00:22:45,153 --> 00:22:47,488 and at an increasing rate. 377 00:22:47,522 --> 00:22:50,591 So it's ice-free during more of the year. 378 00:22:50,625 --> 00:22:52,593 That leaves the shore here 379 00:22:52,627 --> 00:22:55,129 more exposed to erosion from storms, 380 00:22:55,163 --> 00:22:57,464 which are also getting more powerful, 381 00:22:57,499 --> 00:23:00,667 another effect of climate change. 382 00:23:00,702 --> 00:23:03,670 The northern reaches of Alaska, Siberia and Canada 383 00:23:03,705 --> 00:23:05,539 are mostly permafrost, 384 00:23:05,573 --> 00:23:08,976 ground that has been frozen year-round for millennia. 385 00:23:09,010 --> 00:23:10,811 It contains lots of organic matter, 386 00:23:10,845 --> 00:23:13,547 old leaves and roots from plants 387 00:23:13,581 --> 00:23:16,717 that grew thousands of years ago. 388 00:23:16,751 --> 00:23:18,719 Because the Arctic regions are warming faster 389 00:23:18,753 --> 00:23:20,654 than anywhere else on Earth, 390 00:23:20,688 --> 00:23:22,723 the permafrost is thawing 391 00:23:22,757 --> 00:23:25,726 and its contents are rotting, 392 00:23:25,760 --> 00:23:28,395 just like when you unplug the freezer. 393 00:23:31,266 --> 00:23:34,668 The thawing permafrost is releasing carbon dioxide 394 00:23:34,702 --> 00:23:38,238 and methane, an even more potent greenhouse gas, 395 00:23:38,273 --> 00:23:40,007 into the atmosphere. 396 00:23:40,041 --> 00:23:42,409 This is making things even warmer, 397 00:23:42,444 --> 00:23:46,080 another example of a positive feedback mechanism. 398 00:23:46,114 --> 00:23:48,849 The world's permafrost stores enough carbon 399 00:23:48,883 --> 00:23:52,419 to more than double the CO2 in the atmosphere. 400 00:23:52,454 --> 00:23:53,754 At the rate we're going, 401 00:23:53,788 --> 00:23:55,356 global warming could release most of it 402 00:23:55,390 --> 00:23:57,091 by the end of the century. 403 00:23:57,125 --> 00:24:00,527 We might be tipping the climate past a point of no return 404 00:24:00,562 --> 00:24:03,163 into an unpredictable slide. 405 00:24:03,198 --> 00:24:05,999 Okay, the air, the water 406 00:24:06,034 --> 00:24:08,335 and the land are all getting warmer, 407 00:24:08,370 --> 00:24:11,171 so global warming is really happening. 408 00:24:11,206 --> 00:24:13,340 But maybe it's not our fault. 409 00:24:13,375 --> 00:24:15,409 Maybe it's just nature. 410 00:24:15,443 --> 00:24:17,478 Maybe it's the Sun. 411 00:24:18,947 --> 00:24:21,782 No, it's not the Sun. 412 00:24:23,052 --> 00:24:26,354 We've been monitoring the Sun very closely for decades, 413 00:24:26,389 --> 00:24:29,731 and the solar energy output hasn't changed. 414 00:24:30,227 --> 00:24:33,028 What's more, the Earth is warming more at night 415 00:24:33,063 --> 00:24:35,197 than in daytime, 416 00:24:35,232 --> 00:24:38,033 and more in winter than in summer. 417 00:24:38,068 --> 00:24:41,470 That's exactly what we expect from greenhouse warming, 418 00:24:41,505 --> 00:24:43,739 but the opposite of what increased solar output 419 00:24:43,774 --> 00:24:45,775 would cause. 420 00:24:45,811 --> 00:24:48,013 It's now clear beyond any reasonable doubt 421 00:24:48,047 --> 00:24:50,749 that we are changing the climate. 422 00:24:50,783 --> 00:24:52,751 The Sun isn't the problem. 423 00:24:52,785 --> 00:24:54,586 But it is the solution, 424 00:24:54,621 --> 00:24:56,788 and we've known this for a long time, 425 00:24:56,823 --> 00:25:00,459 much longer than you might think. 426 00:25:03,997 --> 00:25:07,533 Paris, September 1878. 427 00:25:07,567 --> 00:25:11,904 The Eiffel Tower won't be built for years to come. 428 00:25:17,511 --> 00:25:20,313 Witness one of the most glorious spectacles 429 00:25:20,347 --> 00:25:23,349 the world has ever seen. 430 00:25:23,384 --> 00:25:26,619 The magnificent head of the Statue of Liberty 431 00:25:26,654 --> 00:25:29,189 has just been completed. 432 00:25:34,328 --> 00:25:37,564 Thousands of exhibitors from around the planet 433 00:25:37,598 --> 00:25:39,800 covered 66 acres of Paris 434 00:25:39,834 --> 00:25:42,102 with their inventions and goods. 435 00:25:42,136 --> 00:25:45,105 Edison's first public demonstration of the lightbulb 436 00:25:45,139 --> 00:25:47,774 will not take place for another year. 437 00:25:47,809 --> 00:25:50,677 There's no such thing as electrical appliances. 438 00:25:50,711 --> 00:25:53,680 People don't flick switches and press buttons. 439 00:25:53,714 --> 00:25:57,317 It's a hand-cranked, horse-drawn world. 440 00:25:58,725 --> 00:26:01,360 That's the guy we came to see, 441 00:26:01,395 --> 00:26:04,196 the one with the crazy moustache. 442 00:26:04,231 --> 00:26:07,233 He's a math teacher named Augustin Mouchot. 443 00:26:07,267 --> 00:26:09,702 Remember, it's 1878. 444 00:26:09,736 --> 00:26:13,172 This is a world lit mostly by gaslight. 445 00:26:13,206 --> 00:26:15,574 The automobile is still years away. 446 00:26:15,609 --> 00:26:19,378 But Mouchot, here, is dazzling the crowd 447 00:26:19,413 --> 00:26:21,347 with his solar power concentrator. 448 00:26:23,417 --> 00:26:26,686 The Sun belongs to all of us! 449 00:26:26,720 --> 00:26:30,890 Even though it is 150 million kilometers away from us, 450 00:26:30,924 --> 00:26:33,059 feel its awesome power! 451 00:26:33,093 --> 00:26:37,063 My invention concentrates the free energy of the Sun 452 00:26:37,097 --> 00:26:40,066 and converts it into mechanical motion. 453 00:26:40,100 --> 00:26:42,702 It can power any kind of machine. 454 00:26:42,736 --> 00:26:47,073 It can produce electricity or run a printing press 455 00:26:47,107 --> 00:26:49,375 or make ice on a hot day. 456 00:26:52,546 --> 00:26:54,046 Et voilà ! 457 00:27:05,225 --> 00:27:06,192 Think of it, 458 00:27:06,226 --> 00:27:08,628 sunlight converted into ice. 459 00:27:08,662 --> 00:27:11,464 You see, my friends, what wonders we can work 460 00:27:11,498 --> 00:27:14,634 if we harness the bounteous energy of the Sun. 461 00:27:14,668 --> 00:27:18,437 The world will someday run out of coal, 462 00:27:18,472 --> 00:27:22,642 but the magnificent Sun will always be there for us. 463 00:27:37,157 --> 00:27:39,625 Mouchot took home the gold medal from the fair. 464 00:27:39,660 --> 00:27:41,460 But the price of coal tumbled, 465 00:27:41,495 --> 00:27:44,964 becoming so cheap that there was no interest in solar energy. 466 00:27:44,998 --> 00:27:47,733 Besides, no one understood, back then, 467 00:27:47,768 --> 00:27:50,469 what the true cost was of burning fossil fuel. 468 00:27:50,504 --> 00:27:53,639 Mouchot's research funding was cut off. 469 00:27:53,674 --> 00:27:58,077 35 years later, in the early years of the 20th century, 470 00:27:58,111 --> 00:28:00,746 another door opened to an alternative future. 471 00:28:00,781 --> 00:28:04,784 It happened in Egypt, on the banks of the Nile. 472 00:28:14,801 --> 00:28:17,769 Memo to future time travelers... 473 00:28:17,804 --> 00:28:20,105 this would be an excellent entry point 474 00:28:20,139 --> 00:28:23,208 for averting climate change. 475 00:28:23,243 --> 00:28:26,211 Egypt, 1913. 476 00:28:26,246 --> 00:28:29,314 That's Frank Shuman of Philadelphia. 477 00:28:31,084 --> 00:28:33,385 He's only had three years of schooling, 478 00:28:33,419 --> 00:28:38,390 but his genius for innovation more than makes up for that. 479 00:28:38,424 --> 00:28:42,461 Before he was 30, Shuman had invented safety glass. 480 00:28:42,495 --> 00:28:47,299 Its use in automobiles and skylights saved countless lives 481 00:28:47,333 --> 00:28:49,635 and made him a very rich man, 482 00:28:49,669 --> 00:28:53,572 rich enough to pursue his real passion, 483 00:28:53,606 --> 00:28:55,807 solar energy. 484 00:28:55,842 --> 00:28:58,076 Shuman led the team that designed and built 485 00:28:58,111 --> 00:29:01,313 an array of solar energy concentrators. 486 00:29:01,347 --> 00:29:04,816 It could power a steam engine. 487 00:29:04,851 --> 00:29:07,986 Shuman is hoping to use the Sun's power 488 00:29:08,021 --> 00:29:09,588 to irrigate the desert 489 00:29:09,622 --> 00:29:11,423 and turn it green. 490 00:29:11,457 --> 00:29:13,058 The official inauguration 491 00:29:13,092 --> 00:29:16,061 of Shuman's solar power plant, in 1913, 492 00:29:16,095 --> 00:29:17,763 was a dazzling success. 493 00:29:21,134 --> 00:29:24,836 He had invented a practical way to tap the Sun's energy 494 00:29:24,871 --> 00:29:27,472 on an industrial scale, 495 00:29:27,507 --> 00:29:31,310 making solar energy even cheaper than coal. 496 00:29:33,279 --> 00:29:35,747 The British and German governments 497 00:29:35,782 --> 00:29:37,749 both offered Shuman generous funding 498 00:29:37,784 --> 00:29:39,651 to develop his invention. 499 00:29:39,686 --> 00:29:42,688 It was the ideal source of abundant power 500 00:29:42,722 --> 00:29:44,690 in tropical regions, 501 00:29:44,724 --> 00:29:48,527 where imported coal was prohibitively expensive. 502 00:29:48,561 --> 00:29:52,297 But Shuman was dreaming even bigger. 503 00:29:52,332 --> 00:29:54,700 In a letter to Scientific American, 504 00:29:54,734 --> 00:29:57,536 he calculated that his solar power plants, 505 00:29:57,570 --> 00:29:59,872 if deployed in an area of the Sahara Desert 506 00:29:59,906 --> 00:30:03,942 only 150 miles on a side, could supply as much power 507 00:30:03,977 --> 00:30:07,112 as consumed by all the industries of the world. 508 00:30:07,146 --> 00:30:09,114 But it was not to be. 509 00:30:09,148 --> 00:30:12,217 The market for a liquid fossil fuel, petroleum, 510 00:30:12,252 --> 00:30:14,052 was exploding for shipping, 511 00:30:14,087 --> 00:30:16,688 home heating, and cars and trucks. 512 00:30:16,723 --> 00:30:19,358 Oil was abundant, cheaper even than coal, 513 00:30:19,392 --> 00:30:22,162 and much easier to get out of the ground and process. 514 00:30:22,296 --> 00:30:26,766 It took 100 men a week to fuel a ship with coal, 515 00:30:26,801 --> 00:30:29,302 but with oil, one man could do the job 516 00:30:29,336 --> 00:30:30,970 in a single day. 517 00:30:31,005 --> 00:30:34,808 A year after Shuman's triumph in the desert, 518 00:30:34,842 --> 00:30:36,583 World War I broke out. 519 00:30:36,677 --> 00:30:40,363 His solar collectors were recycled into weapons. 520 00:30:40,449 --> 00:30:43,383 Frank Shuman's dream of a solar-powered civilization 521 00:30:43,518 --> 00:30:46,025 would have to wait another century 522 00:30:46,360 --> 00:30:48,052 before it was reborn. 523 00:30:49,127 --> 00:30:51,528 There's another inexhaustible source of clean energy 524 00:30:51,562 --> 00:30:53,563 for the world. 525 00:30:55,233 --> 00:30:58,302 The winds themselves are solar powered, 526 00:30:58,336 --> 00:31:02,706 because our star drives the winds and the waves. 527 00:31:02,740 --> 00:31:04,474 Unlike solar collectors, 528 00:31:04,509 --> 00:31:07,644 wind farms take up very little land, 529 00:31:07,679 --> 00:31:09,947 and none at all, if offshore, 530 00:31:09,981 --> 00:31:12,983 where the winds are strongest. 531 00:31:13,017 --> 00:31:15,852 If we could tap even one percent of their power, 532 00:31:15,887 --> 00:31:20,023 we'd have enough energy to run our civilization. 533 00:31:32,105 --> 00:31:35,407 And more solar energy falls on Earth in one hour 534 00:31:35,442 --> 00:31:38,043 than all the energy our civilization consumes 535 00:31:38,078 --> 00:31:39,912 in an entire year. 536 00:31:39,946 --> 00:31:41,714 If we could harness a tiny fraction 537 00:31:41,748 --> 00:31:43,849 of the available solar and wind power, 538 00:31:43,883 --> 00:31:47,019 we could supply all our energy needs forever, 539 00:31:47,053 --> 00:31:50,256 and without adding any carbon to the atmosphere. 540 00:31:58,633 --> 00:32:00,767 It's not too late. 541 00:32:00,802 --> 00:32:02,869 There's a future worth fighting for. 542 00:32:02,904 --> 00:32:04,538 How do I know? 543 00:32:04,572 --> 00:32:07,908 Every one of us comes from a long line of survivors. 544 00:32:07,942 --> 00:32:11,545 Our species is nothing if not adaptive. 545 00:32:11,579 --> 00:32:14,081 It was only because our ancestors learned 546 00:32:14,115 --> 00:32:15,889 to think long-term, and act accordingly, 547 00:32:15,982 --> 00:32:17,746 that we're here at all. 548 00:32:17,820 --> 00:32:19,888 We've had our backs to the wall before, 549 00:32:19,922 --> 00:32:23,024 and we came through to scale new heights. 550 00:32:23,058 --> 00:32:26,561 In fact, the most mythic human accomplishments of all 551 00:32:26,595 --> 00:32:29,330 came out of our darkest hour. 552 00:32:38,735 --> 00:32:40,402 Once there was a world 553 00:32:40,437 --> 00:32:44,907 rigged with 60,000 hair-triggered nuclear weapons. 554 00:32:44,941 --> 00:32:46,542 The combatants were 555 00:32:46,576 --> 00:32:49,211 the two most powerful countries on Earth, 556 00:32:49,246 --> 00:32:51,380 and they were locked in a deadly embrace, 557 00:32:51,414 --> 00:32:53,983 each vowing that they would rather see 558 00:32:54,017 --> 00:32:55,885 everything we love destroyed 559 00:32:55,919 --> 00:32:58,454 than submit to the will of the other. 560 00:32:58,491 --> 00:33:00,458 When I was three years old, 561 00:33:00,493 --> 00:33:03,028 the largest man-made explosion of all time 562 00:33:03,062 --> 00:33:06,498 was detonated by the Soviet Union. 563 00:33:09,636 --> 00:33:12,772 That terror has subsided, to be replaced by new fears. 564 00:33:12,806 --> 00:33:15,508 The danger that the 2,000 largest cities on Earth 565 00:33:15,542 --> 00:33:18,577 would be reduced to rubble in the space of an afternoon 566 00:33:18,612 --> 00:33:21,580 is no longer one of them. 567 00:33:21,615 --> 00:33:24,250 The nuclear rivalry between the United States 568 00:33:24,284 --> 00:33:25,284 and the Soviet Union 569 00:33:25,318 --> 00:33:29,588 had another by-product. 570 00:33:29,623 --> 00:33:32,692 The Apollo missions to the Moon were an extension 571 00:33:32,726 --> 00:33:36,429 of the arms race that raged between them. 572 00:33:36,463 --> 00:33:38,531 Sending people to orbit the Earth 573 00:33:38,565 --> 00:33:41,600 or go to the Moon requires big, reliable, 574 00:33:41,635 --> 00:33:45,004 powerful rockets-- precisely the same technology 575 00:33:45,038 --> 00:33:47,773 you need to carry a nuclear warhead 576 00:33:47,808 --> 00:33:49,342 halfway around the planet 577 00:33:49,376 --> 00:33:53,512 to destroy your enemy's largest cities. 578 00:33:54,516 --> 00:33:56,317 I believe that this nation 579 00:33:56,352 --> 00:33:59,520 should commit itself to achieving the goal, 580 00:33:59,555 --> 00:34:03,358 before this decade is out, of landing a man on the Moon 581 00:34:03,392 --> 00:34:06,794 and returning him safely to the Earth. 582 00:34:06,829 --> 00:34:09,564 President Kennedy's 1961 speech 583 00:34:09,598 --> 00:34:11,899 electrified the nation, 584 00:34:11,934 --> 00:34:15,303 and it contained much that was remarkably prophetic-- 585 00:34:15,337 --> 00:34:17,805 but not a word about a scientific objective 586 00:34:17,840 --> 00:34:19,807 for going to the Moon. 587 00:34:19,842 --> 00:34:22,076 No questions about the Moon's origin 588 00:34:22,111 --> 00:34:25,213 or the hope of bringing back samples to analyze. 589 00:34:25,247 --> 00:34:28,082 No, the Apollo missions were conceived 590 00:34:28,117 --> 00:34:30,485 as a demonstration of the superior power 591 00:34:30,519 --> 00:34:33,521 and precision of our strategic missiles. 592 00:34:33,555 --> 00:34:35,857 But a funny thing happened to us 593 00:34:35,891 --> 00:34:39,093 on our way to the Moon. 594 00:34:39,428 --> 00:34:41,696 We looked homeward... 595 00:34:41,730 --> 00:34:43,869 and discovered another world-- 596 00:34:43,900 --> 00:34:45,534 our own. 597 00:34:45,568 --> 00:34:48,870 For the first time, we inhabitants of Earth 598 00:34:48,905 --> 00:34:52,033 could step back and see it as it really is-- 599 00:34:52,076 --> 00:34:54,644 one world, indivisible, 600 00:34:54,678 --> 00:34:57,747 and kind of small in the cosmic context. 601 00:34:59,284 --> 00:35:02,219 Whatever the reason we first mustered the enormous resources 602 00:35:02,254 --> 00:35:04,655 required for the Apollo program, 603 00:35:04,689 --> 00:35:07,491 however mired it was in Cold War nationalism 604 00:35:07,525 --> 00:35:09,560 and the instruments of death, 605 00:35:09,594 --> 00:35:12,563 the inescapable recognition of the unity 606 00:35:12,597 --> 00:35:14,565 and fragility of the Earth 607 00:35:14,599 --> 00:35:17,101 is its clear and luminous dividend, 608 00:35:17,135 --> 00:35:19,570 the unexpected gift of Apollo. 609 00:35:19,604 --> 00:35:22,773 A project conceived in deadly competition 610 00:35:22,807 --> 00:35:26,110 made us recognize our community. 611 00:35:36,288 --> 00:35:39,957 What titan built this wonder of the world? 612 00:35:41,060 --> 00:35:44,062 It was the Ifugao people of the Philippines, 613 00:35:44,096 --> 00:35:47,332 working with not much more than their hands. 614 00:35:47,366 --> 00:35:52,003 About 10,000 years ago, our ancestors all over the world 615 00:35:52,037 --> 00:35:55,573 took advantage of another form of climate change, 616 00:35:55,608 --> 00:35:59,844 the gentler climate of the intermission in the ice age-- 617 00:35:59,879 --> 00:36:03,414 they invented agriculture. 618 00:36:03,449 --> 00:36:05,583 They gave up the ceaseless wandering, 619 00:36:05,618 --> 00:36:08,887 hunting and gathering that had been their way of life 620 00:36:08,921 --> 00:36:10,889 for a million years or so, 621 00:36:10,923 --> 00:36:14,526 to settle down and produce food. 622 00:36:14,527 --> 00:36:17,036 They found a way to harvest 623 00:36:17,047 --> 00:36:19,946 ten to a hundred times more solar energy 624 00:36:19,950 --> 00:36:24,721 than the environment naturally provided for their ancestors. 625 00:36:24,755 --> 00:36:28,258 People all over the world made the difficult transition 626 00:36:28,292 --> 00:36:31,561 from nomadic cultures to agricultural ones 627 00:36:31,595 --> 00:36:34,797 that used solar energy more efficiently. 628 00:36:34,832 --> 00:36:38,434 It gave rise to civilization. 629 00:36:38,469 --> 00:36:42,005 We stand on the shoulders of those who did the hard work 630 00:36:42,039 --> 00:36:45,608 that such a fundamental transformation required. 631 00:36:45,643 --> 00:36:49,012 Now... it's our turn. 632 00:36:53,884 --> 00:36:56,452 Once there was a world... 633 00:37:01,292 --> 00:37:05,194 If life ever existed on Venus, it would have had no chance 634 00:37:05,229 --> 00:37:08,831 to avert the hellish destiny of this world. 635 00:37:10,467 --> 00:37:14,103 This runaway greenhouse effect was unstoppable. 636 00:37:23,484 --> 00:37:25,218 Once... 637 00:37:25,252 --> 00:37:27,453 there was a world... 638 00:37:29,456 --> 00:37:31,591 ours. 639 00:37:31,625 --> 00:37:34,260 And that world is now. 640 00:37:34,295 --> 00:37:36,763 There are no scientific or technological obstacles 641 00:37:36,797 --> 00:37:38,631 to protecting our world 642 00:37:38,666 --> 00:37:42,101 and the precious life that it supports. 643 00:37:42,136 --> 00:37:44,003 It all depends... 644 00:37:44,038 --> 00:37:47,006 on what we truly value... 645 00:37:47,041 --> 00:37:50,677 and if we can summon the will to act. 646 00:38:38,021 --> 00:38:40,189 But why, some say, the Moon? 647 00:38:40,223 --> 00:38:43,359 Why choose this as our goal? 648 00:38:43,393 --> 00:38:45,494 And they may well ask, 649 00:38:45,529 --> 00:38:47,997 why climb the highest mountain? 650 00:38:48,031 --> 00:38:51,267 We choose to go to the Moon... 651 00:38:51,301 --> 00:38:53,369 we choose to go to the Moon... 652 00:38:58,943 --> 00:39:01,478 ...we choose to go to the Moon in this decade 653 00:39:01,513 --> 00:39:03,347 and do the other things, 654 00:39:03,381 --> 00:39:07,017 not because they are easy, but because they are hard.