Researchers observed a spike in carbon dioxide's greenhouse effect on our planet's surface for the first time.
After taking measurements in two North American locations over a period of 11 years, a team of scientists noticed an increasing capacity for atmospheric carbon to absorb thermal radiation from Earth's surface, which is believed to be linked to rises in fossil fuel emissions, Berkeley Lab reported.
The findings support past predictions of human activity's influence on the greenhouse effect, and also back up the accuracy of current climate models. To make their finding, the researchers looked at CO2's influence on radiative forcing ("a measure of how much the planet's energy balance is perturbed by atmospheric changes") by taking measurements at one site in Oklahoma and another in Alaska.
Positive radiative forces are believed to occur when the Earth absorbs more energy from the Sun that it emits back into space. The measurements revealed CO2 was responsible for a boost in radiative forcing at both locations of about two-tenths of a Watt per square meter per decade. The researchers were able to link this phenomenon to a 22 parts-per-million increase in atmospheric CO2 that occured between 2000 and 2010, most of which comes from the burning of fossil fuels.
"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," said Daniel Feldman, a scientist in Berkeley Lab's Earth Sciences Division and lead author of the Nature paper. "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."
The measurements were taken using spectroscopic instruments that measured the thermal energy that moves from the atmosphere to the Earth's surface. Other instruments detected signatures of other sources of infrared energy, such as clouds and water vapor, allowing researchers to pinpoint signals linked exclusively to CO2.
Both measurements showed atmospheric CO2 emitted a rising amount of infrared energy at about 10 percent of the trend from all sources. The data revealed a link between the boost in CO2-caused radiative forcing and the burning of fossil fuels. The findings also revealed for the first time that photosynthesis has an influence on CO2-attributed radiative forcing, which drops in the spring when plants pull more greenhouse gas out of the atmosphere.
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