An observationally based constraint on the water-vapor feedback

TitleAn observationally based constraint on the water-vapor feedback
Publication TypeJournal Article
Year of Publication2013
JournalJournal of Geophysical Research: Atmospheres
Volume118
Pages12,435–12,443
Date Published11/2013
Abstract / Summary

The increase in atmospheric concentrations of water vapor with global warming is a large positive feedback in the climate system. Thus, even relatively small errors in its magnitude can lead to large uncertainties in predicting climate response to anthropogenic forcing. This study incorporates observed variability of water vapor over 2002–2009 from the Atmospheric Infrared Sounder instrument into a radiative transfer scheme to provide constraints on this feedback. We derive a short-term water vapor feedback of 2.2 ± 0.4 Wm−2K−1. Based on the relationship between feedback derived over short and long timescales in twentieth century simulations of 14 climate models, we estimate a range of likely values for the long-term twentieth century water vapor feedback of 1.9 to 2.8 Wm−2K−1. We use the twentieth century simulations to determine the record length necessary for the short-term feedback to approach the long-term value. In most of the climate models we analyze, the short-term feedback converges to within 15% of its long-term value after 25 years, implying that a longer observational record is necessary to accurately estimate the water vapor feedback.

URLhttp://onlinelibrary.wiley.com/doi/10.1002/2013JD020184/abstract
DOI10.1002/2013JD020184
Journal: Journal of Geophysical Research: Atmospheres
Year of Publication: 2013
Volume: 118
Pages: 12,435–12,443
Date Published: 11/2013

The increase in atmospheric concentrations of water vapor with global warming is a large positive feedback in the climate system. Thus, even relatively small errors in its magnitude can lead to large uncertainties in predicting climate response to anthropogenic forcing. This study incorporates observed variability of water vapor over 2002–2009 from the Atmospheric Infrared Sounder instrument into a radiative transfer scheme to provide constraints on this feedback. We derive a short-term water vapor feedback of 2.2 ± 0.4 Wm−2K−1. Based on the relationship between feedback derived over short and long timescales in twentieth century simulations of 14 climate models, we estimate a range of likely values for the long-term twentieth century water vapor feedback of 1.9 to 2.8 Wm−2K−1. We use the twentieth century simulations to determine the record length necessary for the short-term feedback to approach the long-term value. In most of the climate models we analyze, the short-term feedback converges to within 15% of its long-term value after 25 years, implying that a longer observational record is necessary to accurately estimate the water vapor feedback.

DOI: 10.1002/2013JD020184
Citation:
Gordon, ND, AK Jonko, PM Forster, and KM Shell.  2013.  "An observationally based constraint on the water-vapor feedback."  Journal of Geophysical Research: Atmospheres 118: 12435–12443.  https://doi.org/10.1002/2013JD020184.