Spectroscopic measurements of Earth’s atmosphere have provided the first directly observed evidence that rising levels of atmospheric carbon dioxide are altering Earth’s surface energy balance, a parameter known as radiative forcing (Nature 2015, DOI: 10.1038/nature14240). The finding supports climate model results showing that CO2 emissions are causing Earth to warm. Radiative forcing is influenced up or down by a host of factors, including greenhouse gases, aerosols, ozone, and how Earth’s surface absorbs heat from the sun. Relative to preindustrial times, the value is currently positive and climbing steadily, but scientists have not had reliable direct observations of radiative forcing until now. A team led by Daniel R. Feldman of Lawrence Berkeley National Laboratory examined infrared measurements from Lamont, Okla., and Oliktok Point, Alaska, from 2000 to 2010. The researchers determined that the 22-ppm increase in atmospheric CO2 over that period led to a 0.2-W/m2 increase in surface radiative forcing for the decade, with a spring-fall seasonal variation of about 0.1 W/m2. Earth’s total radiative forcing in the atmosphere is currently about 2.3 W/m2, of which CO2’s contribution stands at about 1.8 W/m2, according to the Intergovernmental Panel on Climate Change.