Oceans and Climate. Caroline Katsman. KNMI Global Climate Division

Transcription

1 Oceans and Climate Caroline Katsman KNMI Global Climate Division Aimée Slangen, Roderik van de Wal (IMAU, Utrecht University) Sybren Drijfhout, Wilco Hazeleger (KNMI, Global Climate) Bert Vermeersen (NIOZ/Delft Technical University)

2 Large-scale ocean circulation driven at the surface, by fluxes of momentum (wind) heat fresh water (evaporation-precipitation) density sea water = function(t,salinity) surface (~ 1000 m): wind-driven circulation deep ocean: thermohaline circulation

3 This lecture i. observing the ocean ii. characteristics ocean circulation iii. ocean and climate abrupt changes in the thermohaline circulation sea level rise

4 ocean observations

5 Observations hydrographic sections: CTD (Conductivity- Temperature-Depth) XBT (expandable BathyThermograph) water samples (O 2, nutrients) moored instruments current meters CTDs

6 Observations satellites: sea surface height currents sea surface temperature ocean color (biological activity) autonomous instruments: profiling floats 2 km depth

7 Argo float network

8 Atlantic Ocean section salinity WOCE section A16 (25 W, Atlantic Ocean) final contact with atmosphere determines characteristics (T,S,O 2..)

9 ocean circulation

10 wind-driven circulation large-scale gyres

11 wind-driven circulation large-scale gyres strong currents on the western side of ocean basins

12 wind-driven circulation large-scale gyres strong currents on the western side of ocean basins Antarctic Circumpolar Current

13 thermohaline circulation currents driven by variations in ocean density (T, S) z deep convection mixing and upwelling spreading EQ geometry basins / forcing determine convection characteristics convective end product differ specific watermasses at selected locations/depths

14 The ocean conveyor belt [Broecker, 1991]

15 convective watermasses NADW AABW NADW: warm (+2 C) salty (35 ) AABW: cold (-2 C) fresh (34.6 )

16 heat transport by oceans thermohaline circulation Atlantic Ocean wind-driven gyres Pacific Ocean small-scale instabilities Southern Ocean [Trenberth and Caron, 2001] 60 S EQ 60 N

17 oceans & climate abrupt changes in the thermohaline circulation

18 multiple equilibria S equator N temperature-driven

19 multiple equilibria S equator N S equator N temperature-driven salinity-driven

20 multiple equilibria temperature strength circulation salinity ratio salinity/temperature-forcing

21 in a warming climate heat uptake melt water S equator N S equator N temperature-driven salinity-driven

22 multiple equilibria temperature strength circulation possible abrupt change salinity ratio salinity/temperature-forcing

23 abrupt change in the past Younger Dryas ( BP): Greenland: -15 C Western Europe: -5 C linked to reduction thermohaline circulation

24 abrupt changes in the future forced collapse forced collapse + greenhouse gas forcing [ what if scenario] just after collapse

25 abrupt changes in the future forced collapse forced collapse + GHG just after collapse T T 2000

26 abrupt changes in the future Netherlands

27 oceans & climate sea level rise

28 Global mean sea level rise reconstructions IPCC 5AR (2013)

29 Global mean sea level rise reconstructions tide gauges IPCC 5AR (2013)

30 Global mean sea level rise reconstructions tide gauges satellites IPCC 5AR (2013)

31 Global mean sea level rise reconstructions tide gauges satellites 3.2 mm/yr 1.7 mm/yr IPCC 5AR (2013)

32 Sea level budget [ ] IPCC 5AR

33 Sea level budget [ ] IPCC 5AR

34 Sea level projections summed contributions of individual components global mean thermal expansion glaciers & ice caps Greenland Antarctica

35 Sea level projections summed contributions of individual components global mean thermal expansion cm IPCC 5AR (2013) glaciers & ice caps Greenland Antarctica

36 oceans & climate regional sea level rise

37 Observed sea level change global mean natural variability + spatially varying long-term trends

38 Causes regional differences changes in ocean density and dynamics + atmospheric loading

39 Causes regional differences changes in Earth s gravity field changing ice sheet mass distribution gravity field state of rest ocean surface geoid NASA

40 Self-gravitation effect gravitational pull on ocean towards large (ice)mass ice sheet

41 Self-gravitation effect ice mass loss melt water added to the ocean ice sheet

42 Self-gravitation effect ice mass loss melt water added to the ocean sea level tilts sea level drop ice sheet

43 Self-gravitation effect ice mass loss melt water added to the ocean sea level tilts rise < global mean ice sheet

44 Self-gravitation effect ice mass loss melt water added to the ocean sea level tilts ice sheet rise > global mean

45 Self-gravitation effect sea level fingerprint Melt water distribution Mitrovica et al (2001)

46 Glacial Isostatic Adjustment

47 Land water storage building of dams NOTE: self-gravitation needs to be accounted for groundwater mining

48 Regional projections ocean expansion glaciers & ice caps Greenland Antarctica GIA land storage

49 Moderate Warm 0.12 m 0.22 m

50 Moderate Warm 0.18 m 0.27 m

51 Moderate Warm 0.07 m 0.09 m

52 Moderate Warm scenario independent 0.15 m

53 Moderate Warm scenario independent 0.0 m

54 Moderate Warm 0.52 m 0.71m

55 Spatial variations

56 Moderate Warm

57 To conclude The oceans plays an important role in climate and (natural and forced) climate change, but we still know surprisingly little about them

58 To conclude The oceans are the principal reservoir for the storage of CO 2, of heat and of ignorance (Walter Munk, The Evolution of Physical Oceanography in the Last Hundred Years, 2002)

59

60 Ocean heat uptake Levitus et al 2009 Levitus et al (2009) m % energy content change ( 93-03) [data source: IPCC (2007)]

61 Caveats sea level projections vertical land movement (natural and human-induced) Jakarta: cm/yr subsidence

62 Caveats sea level projections vertical land movement ocean ice sheet interactions glacier acceleration triggered by ocean warming Holland et al. (Nat. Geosc., 2008)

63 Caveats sea level projections vertical land movement ocean ice sheet interactions ice sheet ocean interactions melt water affects ocean dynamics and sea level Stammer (JGR, 2008)

64 Caveats sea level projections vertical land movement ocean ice sheet interactions ice sheet ocean interactions marginal seas are not resolved IPCC 4AR models IPCC 5AR models

65 AN INTEGRATED FLOOD RISK ASSESSMENT FOR THE NETHERLANDS

66 Sea level projections focused mostly on likely, global mean change coastal protection regional change, worst-case scenario

67 Integrated flood risk assessment Katsman et al (Clim. Change, 2011)

68 Ice sheet dynamics Greenland: - Extrapolation of observations

69 Ice sheet dynamics Greenland - Extrapolation of observations Antarctica persistence / acceleration of observed changes in - Amundsen Sea Embayment - marine glaciers East Antarctica - northern Antarctic Peninsula

70 Storms & surges wind speed current climate future climate Sterl et al (Oce. Sci, 2009)

71 Storms & surges wind speed current climate future climate surge height current climate future climate Sterl et al (Oce. Sci, 2009)

72 Extreme river discharge 1:1250 year discharge of the Rhine river increases by 5 to 40% due to changes in the amount and character of precipitation in the catchment area Beersma et al (2008)

73 Extreme river discharge 1:1250 year discharge of the Rhine river increases by 5 to 40% due to changes in the amount and character of precipitation in the catchment area upstream flooding in Germany will reduce the peak discharge before it reaches the Netherlands extreme discharge increases by 10% Beersma et al (2008)

74 Impacts: Rotterdam harbour Maeslant storm surge barrier - closure frequency current: once every 10 years Katsman et al (Clim. Change, 2011)

75 Impacts: Rotterdam harbour Maeslant storm surge barrier - closure frequency current: once every 10 years 2100, with extreme sea level rise: once every few years few months Katsman et al (Clim. Change, 2011)

76 Impacts: Rotterdam harbour Maeslant storm surge barrier - closure frequency current: once every 10 years 2100, with extreme sea level rise: once every few years few months - larger chance that closure of the barrier coincides with high river discharge quantifying that risk Katsman et al (Clim. Change, 2011)