Observational determination of surface radiative forcing by CO2 from 2000 to 2010.
The climatic impact of CO2 and other greenhouse gases is usually quantified in terms of radiative forcing, calculated as the difference between estimates of the Earth's radiation field from pre-industrial and present-day concentrations of these gases. Radiative transfer models calculate that the increase in CO2 since 1750 corresponds to a global annual-mean radiative forcing at the tropopause of 1.82 ± 0.19 W m(-2) (ref. 2). However, despite widespread scientific discussion and modelling of the climate impacts of well-mixed greenhouse gases, there is little direct observational evidence of the radiative impact of increasing atmospheric CO2. Here we present observationally based evidence of clear-sky CO2 surface radiative forcing that is directly attributable to the increase, between 2000 and 2010, of 22 parts per million atmospheric CO2. The time series of this forcing at the two locations-the Southern Great Plains and the North Slope of Alaska-are derived from Atmospheric Emitted Radiance Interferometer spectra together with ancillary measurements and thoroughly corroborated radiative transfer calculations. The time series both show statistically significant trends of 0.2 W m(-2) per decade (with respective uncertainties of ±0.06 W m(-2) per decade and ±0.07 W m(-2) per decade) and have seasonal ranges of 0.1-0.2 W m(-2). This is approximately ten per cent of the trend in downwelling longwave radiation. These results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions, and provide empirical evidence of how rising CO2 levels, mediated by temporal variations due to photosynthesis and respiration, are affecting the surface energy balance.
Lawrence Berkeley National Laboratory, Earth Sciences Division, 1 Cyclotron Road, MS 74R-316C, Berkeley, California 94720, USA.
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DR
Feldman
1] Lawrence Berkeley National Laboratory, Earth Sciences Division, 1 Cyclotron Road, MS 74R-316C, Berkeley, California 94720, USA [2] University of California-Berkeley, Department of Earth and Planetary Science, 307 McCone Hall, MC 4767, Berkeley, California 94720, USA.
W D
WD
Collins
University of Wisconsin-Madison, Space Science and Engineering Center, 1225 W. Dayton Street, Madison, Wisconsin 53706, USA.
P J
PJ
Gero
1] Lawrence Berkeley National Laboratory, Earth Sciences Division, 1 Cyclotron Road, MS 74R-316C, Berkeley, California 94720, USA [2] University of California-Berkeley, Energy and Resources Group, Berkeley, 310 Barrows Hall, MC 3050, California 94720, USA.
M S
MS
Torn
Atmospheric and Environmental Research, Inc., 131 Hartwell Avenue, Lexington, Massachusetts 02141, USA.
E J
EJ
Mlawer
Pacific Northwest National Laboratory, Fundamental and Computational Sciences, 902 Battelle Boulevard, Richland, Washington 99354, USA.
T R
TR
Shippert
D000413:Alaska; D001272:Atmosphere / Q000737:chemistry; D002245:Carbon Dioxide / Q000032:analysis; D019069:Cell Respiration; D017752:Greenhouse Effect / Q000706:statistics & numerical data; D007259:Infrared Rays; D008962:Models, Theoretical; D019370:Observation; D010788:Photosynthesis; D012621:Seasons; D013997:Time Factors
D002245:Carbon Dioxide