title: Clouds enhance Greenland ice sheet meltwater runoff.
abstract: The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m(-2). Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise.
authors.affiliation: KU Leuven, Department of Earth and Environmental Sciences, Celestijnenlaan 200E, Leuven 3001, Belgium.
authors.forename: K
authors.identifier: http://orcid.org/0000-0001-5727-9098
authors.initials: K
authors.lastname: Van Tricht
authors.affiliation: KU Leuven, Department of Earth and Environmental Sciences, Celestijnenlaan 200E, Leuven 3001, Belgium.
authors.forename: S
authors.identifier: http://orcid.org/0000-0002-1622-0177
authors.initials: S
authors.lastname: Lhermitte
authors.affiliation: Institute for Marine and Atmospheric research Utrecht-Utrecht University, Utrecht 3584CC, The Netherlands.
authors.forename: J T M
authors.initials: JT
authors.lastname: Lenaerts
authors.affiliation: KU Leuven, Department of Earth and Environmental Sciences, Celestijnenlaan 200E, Leuven 3001, Belgium.
authors.forename: I V
authors.initials: IV
authors.lastname: Gorodetskaya
authors.affiliation: Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: T S
authors.initials: TS
authors.lastname: L'Ecuyer
authors.affiliation: Institute for Marine and Atmospheric research Utrecht-Utrecht University, Utrecht 3584CC, The Netherlands.
authors.forename: B
authors.initials: B
authors.lastname: Noël
authors.affiliation: Institute for Marine and Atmospheric research Utrecht-Utrecht University, Utrecht 3584CC, The Netherlands.
authors.forename: M R
authors.initials: MR
authors.lastname: van den Broeke
authors.affiliation: National Severe Storms Laboratory, NOAA, Norman, Oklahoma 73072, USA.
authors.forename: D D
authors.initials: DD
authors.lastname: Turner
authors.affiliation: KU Leuven, Department of Earth and Environmental Sciences, Celestijnenlaan 200E, Leuven 3001, Belgium.
authors.forename: N P M
authors.initials: NP
authors.lastname: van Lipzig