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...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Veröffentlicht in:Nature geoscience 2018-04, Vol.11 (4), p.238-243
Hauptverfasser: Feldman, D. R., Collins, W. D., Biraud, S. C., Risser, M. D., Turner, D. D., Gero, P. J., Tadić, J., Helmig, D., Xie, S., Mlawer, E. J., Shippert, T. R, Torn, M. S.
Format: Artikel
Sprache:eng
Schlagworte:
Online-Zugang:Volltext
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Beschreibung
Zusammenfassung: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 2  yr −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 2 O) and CH 4 to explain the observations fully. Thus, the determination of CH 4 radiative forcing requires accurate observations of both the spatiotemporal distribution of CH 4 and the vertically resolved trends in H 2 O. Observations of the radiative forcing from methane at the Earth’s surface are influenced by absorption effects from water vapour, according to spectroscopic measurements and line-by-line calculations.
ISSN:1752-0894
1752-0908
DOI:10.1038/s41561-018-0085-9