Letter | Published:

Observational determination of surface radiative forcing by CO2 from 2000 to 2010

Nature volume 519, pages 339343 (19 March 2015) | Download Citation

Abstract

The climatic impact of CO2 and other greenhouse gases is usually quantified in terms of radiative forcing1, 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 spectra3 together with ancillary measurements and thoroughly corroborated radiative transfer calculations4. 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 radiation5,6,7. 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.

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Acknowledgements

This material is based upon work supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division, of the US Department of Energy under Award Number DE-AC02-05CH11231 as part of the Atmospheric System Research Program and the Atmospheric Radiation Measurement (ARM) Climate Research Facility Southern Great Plains. We used resources of the National Energy Research Scientific Computing Center (NERSC) under that same award. I. Williams, W. Riley, and S. Biraud of the Lawrence Berkeley National Laboratory, and D. Turner of the National Severe Storms Laboratory also provided feedback. The Broadband Heating Rate Profile (BBHRP) runs were performed using Pacific Northwest National Laboratory (PNNL) Institutional Computing at PNNL, with help from K. Cady-Pereira of Atmospheric Environmental Research, Inc., L. Riihimaki of PNNL, and D. Troyan of Brookhaven National Laboratory.

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Affiliations

  1. Lawrence Berkeley National Laboratory, Earth Sciences Division, 1 Cyclotron Road, MS 74R-316C, Berkeley, California 94720, USA

    • D. R. Feldman
    • , W. D. Collins
    •  & M. S. Torn
  2. University of California-Berkeley, Department of Earth and Planetary Science, 307 McCone Hall, MC 4767, Berkeley, California 94720, USA

    • W. D. Collins
  3. University of Wisconsin-Madison, Space Science and Engineering Center, 1225 W. Dayton Street, Madison, Wisconsin 53706, USA

    • P. J. Gero
  4. University of California-Berkeley, Energy and Resources Group, Berkeley, 310 Barrows Hall, MC 3050, California 94720, USA

    • M. S. Torn
  5. Atmospheric and Environmental Research, Inc., 131 Hartwell Avenue, Lexington, Massachusetts 02141, USA

    • E. J. Mlawer
  6. Pacific Northwest National Laboratory, Fundamental and Computational Sciences, 902 Battelle Boulevard, Richland, Washington 99354, USA

    • T. R. Shippert

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Contributions

D.R.F. implemented the study design, performed the analysis of all measurements from the ARM sites, and wrote the manuscript. W.D.C. proposed the study design and oversaw its implementation. P.J.G. is the AERI instrument mentor and ensured the proper use of spectral measurements and quality control. M.S.T. mentored the implementation of the study and oversaw its funding. E.J.M. and T.R.S. performed calculations and analysis to determine fair-weather bias. All authors discussed the results and commented on and edited the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to D. R. Feldman.

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https://doi.org/10.1038/nature14240

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