WEBVTT FILE 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 3 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.