Implications of changes in freshwater flux from the Greenland ice sheet for the climate of the 21st century

Abstract

Two simulations of the 21st century climate have been carried out using, on the one hand, a coarse resolution climate general circulation model and, on the other hand, the same model coupled to a comprehensive model of the Greenland ice sheet. Both simulations display a gradual global warming up to 2080. In the experiment that includes an interactive ice sheet component, a strong and abrupt weakening of the North Atlantic thermohaline circulation occurs at the end of the 21st century. This feature is triggered by an enhanced freshwater input arising mainly from a partial melting of the Greenland ice sheet. As a consequence of the circulation decline, a marked cooling takes place over eastern Greenland and the northern North Atlantic. This result underlines the potential role of the Greenland ice sheet in the evolution of climate over the 21st century.

Current estimates of freshwater flux through Arctic and subarctic seas

“…Though our direct measurements are too brief as yet to comment, the analysis of the historic hydrographic record and modelling appear to agree that the efflux of freshwater from the Arctic has increased steadily over recent decades (Curry and Mauritzen, 2005), and model-based projections suggest that this will continue, reflecting increased circumarctic river inputs (Wu et al, 2005), a progressive thinning and retraction of the Arctic perennial sea-ice (eg Comiso, 2002), an increase in the freshwater production of Greenland (Fichefet et al, 2003) and increases in the combined ice and freshwater outflows through the CAA and Fram Strait (eg Haak et al, 2005).…”

“…The freshwater flux from Greenland is expected to increase. As one recent example based on a mix of modelling techniques, simulations by Fichefet et al (2003) indicate that the annual mean total freshwater flux from Greenland will increase by 15 mSv over the period 1970-2080. Jeff Ridley (Hadley Centre pers.…”

“…These estimates of calving are essentially identical to the total ice discharge of 11 mSv measured by Rignot and Kanagaratnam (2006) using satellite radar interferometry. Thus although it is anticipated by Fichefet et al (2003) that the annual mean total freshwater flux from Greenland will increase by 15 mSv between 1970 and 2080, based on a mix of modelling techniques (see 'Future', Section 5 below), a value of 18 mSv seems appropriate to the present annual freshwater flux from Greenland and is used in Fig. 1.…”

Long-term ice sheet–climate interactions under anthropogenic greenhouse forcing simulated with a complex Earth System Model

“…The discharge of meltwater from the northern hemisphere ice sheets has been proposed as the triggering mechanism for abrupt climate change in the past at the time of the Younger Dryas (Broecker et al 1988;Maier-Reimer and Mikolajewicz 1989). Fichefet et al (2003) found a substantial weakening of the NAMOC in response to increased meltwater fluxes from the GrIS in a twenty-first century simulation. Driesschaert et al (2007) investigated the response of the climate system to different greenhouse gas scenarios with a three-dimensional (3D) EMIC including a dynamic ice sheet component.…”

“…For the studies of past climates, Intermediate Complexity Models (EMICs, for an overview see Petoukhov et al 2005) have been used as tool, due to the long time scales and the limitations imposed by computational resources. For future climate projections, some studies have focused exclusively on the feedbacks between ice sheets and ocean (Huybrechts et al 2002;Fichefet et al 2003), while others have investigated the feedbacks between ice sheets and atmosphere as well (Ridley et al 2005;Driesschaert et al 2007). Only the studies of Ridley et al (2005), with HadCM3, and Mikolajewicz et al (2007b) were performed with General Circulation Models (GCMs) both for the ocean and atmosphere, and with full coupling between the three components ice sheet, ocean, and atmosphere.…”