WEBVTT Kind: captions Language: en 00:00:00.190 --> 00:00:04.410 Climate change refers to the change in global climate patterns of the last century. 00:00:04.930 --> 00:00:11.610 Most scientists accept that it is a reality tied to carbon dioxide and other greenhouse gases emitted through human activities, 00:00:11.980 --> 00:00:13.980 including the use of fossil fuels. 00:00:14.170 --> 00:00:16.289 Greenhouse gases trap heat in the Earth's atmosphere, 00:00:16.750 --> 00:00:22.920 causing temperatures to rise. In fact, the ten warmest years on record have all occurred since 1998. So 00:00:23.650 --> 00:00:25.650 how did we get here? In 00:00:26.019 --> 00:00:33.808 1769, James Watts' version of the steam engine was patented, and this innovation led to the widespread use of coal, a major fossil fuel both 00:00:33.809 --> 00:00:37.409 then and now, to power industry, agriculture, and textile production. 00:00:37.870 --> 00:00:43.469 As a result, the productivity of these industries dramatically increased in the period known as the Industrial Revolution. 00:00:44.440 --> 00:00:48.270 Studies reveal the beginnings of a sharp increase in CO2 in the Earth's atmosphere 00:00:49.120 --> 00:00:51.120 corresponding to this period. 00:00:51.129 --> 00:00:55.948 Since then, engines powered by carbon-based fuels have proliferated in cars, planes and ships. 00:00:56.500 --> 00:01:00.090 These fuels are used to generate power and manufacture goods too. 00:01:00.760 --> 00:01:04.500 Activities beyond fossil fuel use also generate greenhouse gas emissions. 00:01:05.170 --> 00:01:08.549 Deforestation is one example, since trees absorb carbon dioxide. 00:01:09.159 --> 00:01:14.219 The amount of CO2 in the atmosphere is higher today than it has been for hundreds of thousands of years. The 00:01:14.439 --> 00:01:21.539 effects are significant and include melting polar ice, rising sea levels, severe storms, droughts and flooding. The 00:01:21.850 --> 00:01:23.850 consequences include widespread destruction, 00:01:24.369 --> 00:01:32.279 particularly for those living in coastal areas and on islands, the extinction of plants and animals, water scarcity, and changing crop and fishery yields. 00:01:32.890 --> 00:01:36.599 Climate change can contribute to hunger, refugee flows and more. 00:01:37.090 --> 00:01:41.579 These consequences will occur unevenly across time and place, but will affect everyone. 00:01:42.310 --> 00:01:48.570 There is wide scientific agreement about the urgent need to address climate change, but less political consensus about how. 00:01:49.659 --> 00:01:55.078 The possibilities can be grouped into three categories: mitigation, adaptation and geoengineering 00:01:56.320 --> 00:01:59.429 Mitigation refers to efforts to reduce or prevent emissions of greenhouse 00:01:59.770 --> 00:02:06.839 gases, whether by increasing the efficiency of fossil fuel use, using cleaner fuels, or preserving or replanting forests. 00:02:07.450 --> 00:02:13.799 Electric and fuel-efficient cars, mass transit, and bike sharing programs are all examples of mitigation efforts. 00:02:14.709 --> 00:02:19.768 Energy use from fossil fuels is a major emission source. But reducing these emissions at a scale that 00:02:19.900 --> 00:02:25.890 prevents the worst effects of climate change, while providing the power necessary for a growing world, is an enormous challenge. 00:02:26.620 --> 00:02:31.440 There are two policy approaches for mitigation efforts: top-down and bottom-up. A 00:02:31.900 --> 00:02:38.250 top-down strategy sets an overall international goal and assigns each country a particular action to fulfill that goal. A 00:02:38.709 --> 00:02:45.149 bottom-up approach does not bind countries to specific steps. The 2015 Paris agreement in which countries themselves 00:02:45.459 --> 00:02:48.539 decided what mitigation actions to take is one prominent example. 00:02:49.599 --> 00:02:54.539 Top-down agreements have proved harder to reach because countries disagree on how to share the burden of cutting emissions. 00:02:55.299 --> 00:02:58.439 Developed powers such as the United States and European countries, 00:02:58.840 --> 00:03:04.410 major developing states such as China and India, and smaller developing countries all have differing views. 00:03:05.620 --> 00:03:08.039 Another policy response is adaptation, 00:03:08.049 --> 00:03:15.689 which aims to reduce the world's exposure to climate changes effects. This includes moving people from areas prone to flooding and using barriers, 00:03:16.269 --> 00:03:20.009 regulations such as building codes, and other steps to protect those who stay. 00:03:20.829 --> 00:03:27.749 Large-scale adaptation, including the relocation of entire island countries, is expensive, and governments differ on who should pay. A 00:03:28.510 --> 00:03:30.400 third policy area, 00:03:30.400 --> 00:03:37.289 geoengineering, aims to reverse climate changes effects such as by releasing particles into the atmosphere to deflect some of the sun's rays. 00:03:37.510 --> 00:03:44.039 But the science remains in development, and the effects are uncertain. There is also no consensus on who would approve any such act. 00:03:44.829 --> 00:03:50.789 Geoengineering is thus controversial, but will likely remain a possibility if climate change and its predicted effects advance. 00:03:51.579 --> 00:03:58.469 Greenhouse gases affect us all, no matter where they are emitted. This problem and the threats it poses require a response 00:03:58.750 --> 00:04:01.830 from governments, businesses and citizens worldwide.