First direct experimental evidence of greenhouse effect at Earth’s surface
For the first time, scientists have observed in an experiment outside the lab an increase in carbon dioxide’s greenhouse effect at the Earth’s surface. The results of the study were reported last week in the journal Nature.
The greenhouse effect where carbon dioxide (CO2) – and other gases – prevents the solar radiation reflected by the Earth’s surface to reach space and, consequently, raises our planet temperature, is well established. However, the effect has never been experimentally confirmed outside the laboratory, at least until now. In the study led by researchers at the US department of Energy Lawrence Berkeley National Laboratory, scientists measured the CO2‘s capacity to absorb thermal radiation emitted from the Earth’s surface. They focused on two different locations in North America – Oklahoma and the North Slope of Alaska – and collected the data for 11 years over the period 2000-2010.
They found that CO2 was responsible for a significant increase in radiative forcing, which is a measure of how much the planet’s energy balance is perturbed by atmospheric changes, at both locations. They were also able to link this trend to the increase in atmospheric CO2 – from fossil fuels – between 2000 and 2010. “We see, for the first time in the field, the amplification of the greenhouse effect because there’s more CO2 in the atmosphere to absorb what the Earth emits in response to incoming solar radiation” – Daniel Feldman, a scientist at the Berkeley Lab said. “Numerous studies show rising atmospheric CO2 concentrations, but our study provides the critical link between those concentrations and the addition of energy to the system, or the greenhouse effect” – Feldman added.
The scientists used precise spectroscopic instruments operated by the Atmospheric Radiation Measurement Climate Research Facility and controlled for factors such as weather systems moving through the area. These instruments, located at the sites in Oklahoma and Alaska, can measure thermal infrared energy that travels down through the atmosphere to the surface and can distinguish the spectral signature of infrared energy of CO2 from that of clouds and water vapour. The combination of these measurements enabled the scientists to isolate the signals attributed solely to CO2. Atmospheric CO2 emitted an increasing amount of infrared energy: 0.2 W/m2 per decade – roughly 10% of the trend from all sources of infrared energy such as clouds and water vapour.
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