1 . Humans are responsible for 25% to 40% more of the total share of methane emissions(甲烷排放)than previously estimated, according to a new study in Nature.
Methane is one of the most powerful and effective greenhouse gases: about 28 times more effective than carbon dioxide at trapping heat in the atmosphere. It's responsible for about a quarter of global warming. It's produced naturally by animals, volcanoes, and wetlands, but it's also a byproduct of oil and gas production. It's this last form of methane that the study focused on.
Researchers used ice core measurements from Greenland from 1750 to 2013, plus previous data from Antarctica. They melted the ice to let the small quantities of ancient air trapped inside come out. These act a bit like time capsules,allowing us to learn about the methane in the atmosphere at the time. They used carbon-14, which comes from living things, as a substitute(替代物)to determine whether the methane they found came from biological sources. Until 1870, around the time when we started using fossil(化石)fuels, almost all methane came from these sources. After that, there was a rise in methane that didn't have any carbon-14, from ancient fossil sources in which carbon-14 had disappeared. That allowed the researchers to compare natural methane with methane caused by human activity.
If more methane is created by humans, there's an even bigger opportunity to control how much we release. Methane stays in the atmosphere for only a decade(compared with 200 years for carbon dioxide). So efforts to cut methane, which mostly comes from the production and transportation of gas and oil, could bring great benefit right away.
1. Which methane source does the study focus on?| A．Animals. | B．Wetlands. | C．Volcanoes. | D．Fossil fuels. |
| A．Methane comes mainly from animals and wetlands. |
| B．There is more methane than carbon dioxide in the air. |
| C．Fossil fuels have been used about a century and a half. |
| D．Methane will remain permanently in the atmosphere. |
| A．Optimistic. | B．Skeptical. | C．Disappointed. | D．Unconcermed |
| A．Fossil Fuels Cause Global Pollution |
| B．Humans Produce More Methane than We Thought |
| C．Methane Is the Biggest Cause for Global Warming |
| D．Carbon Dioxide Has Less Impact on Climate than Methane |
