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Response of the Western European climate to a collapse of the thermohaline circulation

Response of the Western European climate to a collapse of the thermohaline circulation
Response of the Western European climate to a collapse of the thermohaline circulation
Two ensemble simulations with the ECHAM5/MPI-OM climate model have been investigated for the atmospheric response to a thermohaline circulation (THC) collapse. The model forcing was specified from observations between 1950 and 2000 and it followed a rising greenhouse gases emission scenario from 2001 to 2100. In one ensemble, a THC collapse was induced by adding freshwater in the northern North Atlantic, from 2001 onwards. After about 20 years, an almost stationary response pattern develops, that is, after the THC collapse, global mean temperature rises equally fast in both ensembles with the hosing ensemble displaying a constant offset. The atmospheric response to the freshwater hosing features a strong zonal gradient in the anomalous 2-m air temperature over Western Europe, associated with a strong land–sea contrast. Since Western Europe climate features a strong marine impact due to the prevailing westerlies, the question arises how such a strong land–sea contrast can be maintained. We show that a strong secondary cloud response is set up with increased cloud cover over sea and decreased cloud cover over land. Also, the marine impact on Western European climate decreases, which results from a reduced transport of moist static energy from sea to land. As a result, the change in lapse rate over the cold sea surface temperature (SST) anomalies west of the continent is much larger than over land, dominated by changes in moisture content rather than temperature.
climate change, thermohaline circulation, western europe, ocean-atmosphere interactions, land-sea contrast, lapse rate
0930-7575
689-697
Laurian, A.
7901ed3e-43da-4f72-b2f2-e45ac2ff3d56
Drijfhout, S.S.
a5c76079-179b-490c-93fe-fc0391aacf13
Hazeleger, W.
0bd826a1-4713-43ab-aace-3ea59d2fc37e
van den Hurk, B.
967386e0-6d51-4ad1-9c80-ef83dc62981d
Laurian, A.
7901ed3e-43da-4f72-b2f2-e45ac2ff3d56
Drijfhout, S.S.
a5c76079-179b-490c-93fe-fc0391aacf13
Hazeleger, W.
0bd826a1-4713-43ab-aace-3ea59d2fc37e
van den Hurk, B.
967386e0-6d51-4ad1-9c80-ef83dc62981d

Laurian, A., Drijfhout, S.S., Hazeleger, W. and van den Hurk, B. (2010) Response of the Western European climate to a collapse of the thermohaline circulation. Climate Dynamics, 34 (5), 689-697. (doi:10.1007/s00382-008-0513-4).

Record type: Article

Abstract

Two ensemble simulations with the ECHAM5/MPI-OM climate model have been investigated for the atmospheric response to a thermohaline circulation (THC) collapse. The model forcing was specified from observations between 1950 and 2000 and it followed a rising greenhouse gases emission scenario from 2001 to 2100. In one ensemble, a THC collapse was induced by adding freshwater in the northern North Atlantic, from 2001 onwards. After about 20 years, an almost stationary response pattern develops, that is, after the THC collapse, global mean temperature rises equally fast in both ensembles with the hosing ensemble displaying a constant offset. The atmospheric response to the freshwater hosing features a strong zonal gradient in the anomalous 2-m air temperature over Western Europe, associated with a strong land–sea contrast. Since Western Europe climate features a strong marine impact due to the prevailing westerlies, the question arises how such a strong land–sea contrast can be maintained. We show that a strong secondary cloud response is set up with increased cloud cover over sea and decreased cloud cover over land. Also, the marine impact on Western European climate decreases, which results from a reduced transport of moist static energy from sea to land. As a result, the change in lapse rate over the cold sea surface temperature (SST) anomalies west of the continent is much larger than over land, dominated by changes in moisture content rather than temperature.

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More information

Published date: April 2010
Keywords: climate change, thermohaline circulation, western europe, ocean-atmosphere interactions, land-sea contrast, lapse rate
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 348363
URI: http://eprints.soton.ac.uk/id/eprint/348363
ISSN: 0930-7575
PURE UUID: d91923c8-c2c6-4abc-834d-e42c9d2bb292

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Date deposited: 12 Feb 2013 13:13
Last modified: 16 Jul 2019 21:43

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Contributors

Author: A. Laurian
Author: S.S. Drijfhout
Author: W. Hazeleger
Author: B. van den Hurk

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