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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 19 Mar 2019

Submitted as: research article | 19 Mar 2019

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Increased water vapour lifetime due to global warming

Øivind Hodnebrog1, Gunnar Myhre1, Bjørn H. Samset1, Kari Alterskjær1, Timothy Andrews2, Olivier Boucher3,4, Gregory Faluvegi5,6, Dagmar Fläschner7, Piers M. Forster8, Matthew Kasoar9,10, Alf Kirkevåg11, Jean-Francois Lamarque12, Dirk Olivié11, Thomas B. Richardson8, Dilshad Shawki9, Drew Shindell13, Keith P. Shine14, Philip Stier15, Toshihiko Takemura16, Apostolos Voulgarakis9, and Duncan Watson-Parris15 Øivind Hodnebrog et al.
  • 1CICERO Center for International Climate Research, Oslo, Norway
  • 2Met Office Hadley Centre, Exeter, UK
  • 3Institut Pierre-Simon Laplace, Paris, France
  • 4CNRS/Sorbonne Université, Paris, France
  • 5NASA Goddard Institute for Space Studies, New York, USA
  • 6Center for Climate Systems Research, Columbia University, New York, USA
  • 7Max-Planck-Institut für Meteorologie, Hamburg, Germany
  • 8University of Leeds, Leeds, UK
  • 9Department of Physics, Imperial College London, London, UK
  • 10Grantham Institute – Climate Change and the Environment, Imperial College London, London, UK
  • 11Norwegian Meteorological Institute, Oslo, Norway
  • 12NCAR/UCAR, Boulder, USA
  • 13Duke University, Durham, USA
  • 14University of Reading, Reading, UK
  • 15Department of Physics, University of Oxford, UK
  • 16Kyushu University, Fukuoka, Japan

Abstract. The relationship between changes in integrated water vapour (IWV) and precipitation can be characterized by quantifying changes in atmospheric water vapour lifetime. Precipitation isotope ratios correlate with this lifetime, a relationship that helps understand dynamical processes and may lead to improved climate projections. We investigate how water vapour and its lifetime respond to different drivers of climate change, such as greenhouse gases and aerosols. Results from 11 global climate models have been used, based on simulations where CO2, methane, solar irradiance, black carbon (BC), and sulphate have been perturbed separately. A lifetime increase from 8 to 10 days is projected between 1986–2005 and 2081–2100, under a business-as-usual pathway. By disentangling contributions from individual climate drivers, we present a physical understanding of how global warming slows down the hydrological cycle, due to longer lifetime, but still amplifies the cycle due to stronger precipitation/evaporation fluxes. The feedback response of IWV to surface temperature change differs somewhat between drivers. Fast responses amplify these differences and lead to net changes in IWV per degree surface warming ranging from 6.4±0.9 %/K for sulphate to 9.8±2 %/K for BC. While BC is the driver with the strongest increase in IWV per degree surface warming, it is also the only driver with a reduction in precipitation per degree surface warming. Consequently, increases in BC aerosol concentrations yield the strongest slowdown of the hydrological cycle among the climate drivers studied, with a change in water vapour lifetime per degree surface warming of 1.1±0.4 days/K, compared to less than 0.5 days/K for the other climate drivers (CO2, methane, solar irradiance, sulphate).

Øivind Hodnebrog et al.
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Status: final response (author comments only)
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Øivind Hodnebrog et al.
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Publications Copernicus
Short summary
Different greenhouse gases (e.g. CO2) and aerosols (e.g. black carbon) impact the Earth’s water cycle differently. Here we investigate how various gases and particles impact atmospheric water vapour and its lifetime, i.e., the average number of days that water vapour stays in the atmosphere after evaporation and before precipitation. We find that this lifetime could increase by around 25 % near the end of this century, from a present-day value of 8 days, if we follow a business-as-usual pathway.
Different greenhouse gases (e.g. CO2) and aerosols (e.g. black carbon) impact the Earth’s...