1 00:00:00,960 --> 00:00:04,350 Computer models of Earth's atmosphere can tell us a lot. 2 00:00:04,650 --> 00:00:08,430 Trained on how the atmosphere typically operates, the models 00:00:08,430 --> 00:00:12,240 take in data about temperature, wind speed, humidity, and more 4 00:00:12,270 --> 00:00:15,210 to give us important insights into the world around us. 5 00:00:15,870 --> 00:00:19,410 Computer models like NASA's GEOS model can help us study how 6 00:00:19,410 --> 00:00:22,170 chemicals move through the atmosphere, how the ocean 7 00:00:22,170 --> 00:00:25,830 circulates, and where air quality might be affected by fires and 8 00:00:25,830 --> 00:00:30,090 pollution. These models can also provide a look at what might 9 00:00:30,090 --> 00:00:33,870 have been if circumstances were different. For instance, climate 10 00:00:33,870 --> 00:00:36,720 models can forecast how temperatures might change with 11 00:00:36,720 --> 00:00:41,280 different levels of carbon emissions. In 2020, the world 12 00:00:41,280 --> 00:00:44,970 threw the models a new test when people began behaving very, 13 00:00:45,000 --> 00:00:49,380 very differently with almost no warning, a global pandemic 14 00:00:49,380 --> 00:00:53,220 set in. Around the globe, people stopped driving and 15 00:00:53,220 --> 00:00:57,060 flying in large numbers, started staying home, and completely 16 00:00:57,060 --> 00:00:59,850 changed their pollution patterns. In particular 17 00:00:59,910 --> 00:01:03,780 emissions of nitrogen dioxide, a common air pollutant released by 18 00:01:03,780 --> 00:01:07,020 cars, airplanes and many factories, declined 19 00:01:07,050 --> 00:01:11,580 significantly. But just how much did the shutdown change our 20 00:01:11,580 --> 00:01:16,500 emissions? NASA\'92s GEOS atmospheric composition model offers an 21 00:01:16,500 --> 00:01:20,640 answer. The model run functions by assuming that nothing was 22 00:01:20,640 --> 00:01:24,300 different in 2020, that people continued behaving roughly the 23 00:01:24,300 --> 00:01:27,390 same as they would have with no activity shutdowns, adding the 24 00:01:27,390 --> 00:01:31,740 same number of atmospheric pollutants to the air. It's then 25 00:01:31,770 --> 00:01:35,700 a matter of subtraction. Comparing those models to real 26 00:01:35,700 --> 00:01:38,910 world observations made by satellites during the shutdowns 27 00:01:38,940 --> 00:01:42,000 shows how significant the decrease in pollution was in 28 00:01:42,000 --> 00:01:46,080 various cities. Activity shutdowns started in Wuhan, 29 00:01:46,080 --> 00:01:50,760 China. And in January, observed emissions of nitrogen dioxide 30 00:01:50,790 --> 00:01:55,080 began to diverge from what models predicted, about 60% less 31 00:01:55,080 --> 00:01:58,710 than predicted, that is. As the virus and the associated 32 00:01:58,710 --> 00:02:02,310 shutdowns moved west, European cities began to experience 33 00:02:02,310 --> 00:02:06,120 decreased levels of nitrogen dioxide emissions as well. in 34 00:02:06,120 --> 00:02:10,680 Madrid, Spain, nitrogen dioxide emissions were also 60% 35 00:02:10,680 --> 00:02:16,170 less than modeled. Shortly after, cities in the United States 36 00:02:16,200 --> 00:02:21,030 began to follow suit. In March, New York City shut down all but 37 00:02:21,030 --> 00:02:26,370 essential activities and emissions dropped by 45%. 50 of 38 00:02:26,370 --> 00:02:30,750 the 61 analyzed cities show nitrogen dioxide reductions 39 00:02:30,750 --> 00:02:35,610 between 20 and 50% \'97 clearly linking lower NO2 emissions 40 00:02:35,610 --> 00:02:38,460 to pandemic related restrictions, and therefore 41 00:02:38,460 --> 00:02:42,660 human activity. This sudden change in human behavior gives 42 00:02:42,660 --> 00:02:45,360 us new insights into the relationship between human 43 00:02:45,360 --> 00:02:49,650 activities and air pollution, which still has many unanswered 44 00:02:49,650 --> 00:02:54,090 scientific questions. The only way we can fully understand air 45 00:02:54,090 --> 00:02:57,840 pollution is by combining surface observations, satellite 46 00:02:57,840 --> 00:03:02,190 data and computer models. With NASA's satellite monitoring system 47 00:03:02,190 --> 00:03:06,090 and computing capabilities, it's uniquely positioned to provide 48 00:03:06,090 --> 00:03:09,750 detailed information about air quality everywhere in the world.