By Greg Neimeyer
In an unprecedented finding, scientists have now observed a direct connection between the rising levels of atmospheric carbon dioxide and an increase in the amount of thermal radiation that strikes the EarthÔÇÖs surface. The finding confirms a keystone premise of the theory that humans have contributed to worldwide warming in recent decades, the researchers report in an online February 25 of Nature.
Like other greenhouse gasses, carbon dioxide can absorb and re-radiate infrared light back down to Earth, warming the earth by trapping thermal energy around the planet that would otherwise dissipate into space. To determine how large an effect recent human-generated CO2 increases have had on EarthÔÇÖs energy balance, climate scientist Daniel Feldman of the Lawrence Berkeley National Laboratory in California and colleagues monitored the amount of thermal radiation hitting sites in Alaska and Oklahoma on cloudless days. Because CO2 emits light within a signature range of wavelengths, the researchers could differentiate between energy balance changes caused by CO2 and those caused by a range of other factors, such as water vapor.
Over 10 years of systematic observations, the team found that a rise in CO2 concentrations of 22 parts per million elevated the amount of incoming thermal radiation from CO2 by .20 watts per square meter, an increase of about 10 percent. The researchers say their results agree with the theoretical predictions of CO2-driven warming used in simulations of future climate.
Policy Statement – These findings provide some of the most definitive data to date regarding the human contributions to global warming and climate change, and throw into high relief the responsibility we bear for global policy making to continue monitoring and reducing greenhouse gasses to help reduce or reverse the adverse impact of human contributions to global climate change.