Movies map global greenhouse gas movement

 作者:柳坚     |      日期:2017-12-01 07:02:08
By Fred Pearce It’s not exactly an Oscar-winning show, but it is a scientific first. European researchers have produced the first movies of how atmospheric concentrations of the two most important man-made greenhouse gases – carbon dioxide and methane – change with the seasons. The movies cover the period of 2003 to 2005. The data behind the show come from the first space sensor capable of measuring levels of CO2 and methane through the entire depth of the atmosphere. The Scanning Imaging Absorption Spectrometer for Atmospheric Cartography is aboard the European environmental satellite ENVISAT, which was launched in 2002. The sensor observes the spectrum of sunlight shining through the atmosphere. This provides a proxy for concentrations of the gases, because their radiation-trapping properties work at distinct wavelengths. What is most immediately obvious in the two movies is how natural ecosystems “breathe” greenhouse gases. CO2 levels are highest at the end of the winter, before vegetation starts to absorb the gas during the spring growing season. Methane levels are highest in the summer, when forests and swamps release the gas. The researchers say these natural cycles balance out over the year. What nature releases, it later absorbs. But on top of the season variations, however, CO2 shows a strong increase in average annual concentrations (see the movie here). This is caused by human activity, mainly burning fossil fuels, but also deforestation. While the gases eventually mix in the atmosphere, the seasonal short-term “hotspots” revealed in the movies show concentrated sources of emissions, and the “coldspots” reveal sinks, where nature absorbs the gases. Michael Buchwitz at Bremen University in Germany, who compiled the movies, says they have real research value. For instance, the methane movie reveals larger than expected emissions from tropical rainforests, confirming some recent research findings. The next step is to compare the actual geographical and seasonal variations in gas concentrations revealed in the movies with the predictions of models. This, says Buchwitz, should reveal shortcomings in the models and help researchers improve them. The data do not provide direct information on emissions. Nevertheless, they should allow scientists to identify countries that fail to declare all their greenhouse gas emissions to international emissions treaties such as the Kyoto protocol,