Researchers using spectrometers to measure carbon dioxide levels in Earth’s atmosphere between 2000 and 2010 have confirmed that levels of the greenhouse gas are increasing worldwide.
Led by Dan Feldman of the Lawrence Berkeley National Laboratory in California, a team of scientists measured the amount of infrared radiation absorbed by atmospheric gases, specifically carbon dioxide. Increasing levels of atmospheric carbon dioxide are warming the Earth’s surface through a phenomenon known as the greenhouse effect.
Carbon dioxide and other greenhouse gases, such as methane, absorb infrared radiation that would ordinarily be sent into space, in a manner similar to the way a greenhouse traps heat, warming temperatures inside it. This phenomenon, known as radiative forcing, occurs when more energy enters the greenhouse–or in this case, the planet–than leaves it.
Feldman and his team measured radiative forcing at two research locations, one in Oklahoma, and the other above the Arctic Circle near Barrow, Alaska. Both sites are owned by the US Department of Energy.
Using spectrometers set for accuracy by the United States Office of Weights and Measures, the researchers followed infared radiation arriving on Earth’s surface. That infrared radiation is both absorbed and scattered by greenhouse gases in the planet’s atmosphere.
Spectrometers can pinpoint and identify carbon dioxide because like all molecules, it emits and absorbs energy at very specific wavelengths.
At both research sites, carbon dioxide in the atmosphere increased by 22 parts per million from 2000 to 2010. The concept of parts per million refers to the volume of carbon dioxide molecules within a million air molecules.
Levels of infared energy directed down to the Earth’s surface also increased at both sites during this period due to being scattered by carbon dioxide.
Increasing levels of atmospheric carbon dioxide resulted in more infrared energy being reflected back to Earth instead of being emitted into space.
Warming from other sources such as clouds, water vapor, weather, or even faulty instruments was ruled out by the researchers.
“This is clear observational evidence that when we add carbon dioxide to the atmosphere, it will push the system to a warmer place,” Feldman said.
A report on the study is published in the Feb. 25 issue of the journal Nature.
The researchers are now conducting a second study measuring the effect of other greenhouse gases, such as methane, on global warming.