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This content will become publicly available on April 2, 2019

Title: Observationally derived rise in methane surface forcing mediated by water vapour trends

Atmospheric methane (CH 4) mixing ratios exhibited a plateau between 1995 and 2006 and have subsequently been increasing. While there are a number of competing explanations for the temporal evolution of this greenhouse gas, these prominent features in the temporal trajectory of atmospheric CH 4 are expected to perturb the surface energy balance through radiative forcing, largely due to the infrared radiative absorption features of CH 4. However, to date this has been determined strictly through radiative transfer calculations. Here, we present a quantified observation of the time series of clear-sky radiative forcing by CH 4 at the surface from 2002 to 2012 at a single site derived from spectroscopic measurements along with line-by-line calculations using ancillary data. There was no significant trend in CH 4 forcing between 2002 and 2006, but since then, the trend in forcing was 0.026 ± 0.006 (99.7% CI)W m 2yr -1. The seasonal-cycle amplitude and secular trends in observed forcing are influenced by a corresponding seasonal cycle and trend in atmospheric CH 4. However, we find that we must account for the overlapping absorption effects of atmospheric water vapour (H 2O) and CH 4 to explain the observations fully. Thus, the determination of CHmore » 4 radiative forcing requires accurate observations of both the spatiotemporal distribution of CH 4 and the vertically resolved trends in H 2O.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [1] ;  [1] ; ORCiD logo [3] ;  [4] ;  [1] ;  [5] ;  [6] ;  [7] ;  [8] ;  [2]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
  3. National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States)
  4. Univ. of Wisconsin, Madison, WI (United States)
  5. Univ. of Colorado, Boulder, CO (United States)
  6. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  7. Atmospheric and Envrionmental Research, Lexington, KY (United States)
  8. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-741331
Journal ID: ISSN 1752-0894; 895796
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Nature Geoscience
Additional Journal Information:
Journal Volume: 11; Journal Issue: 4; Journal ID: ISSN 1752-0894
Publisher:
Nature Publishing Group
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1458639