The Oceans in a Warming World

Transcription

1 The Oceans in a Warming World John Marshall Earth, Atmospheric and Planetary Sciences 1. Review global observations of warming trends. Ocean temperature trends key part of the puzzle. 2. Discuss timing and regional patterns of warming. Earth is not warming up uniformly. Ocean plays a central role in setting patterns & timing. Explore underlying mechanisms using models. 3. Conclude What s happening and why? forcing time

2 Observed surface ocean currents 20 years of observations Satellite altimetry 50 cms cms -1 Ocean is living fluid full of turbulence across myriad space and timescales Vast reservoir, constantly exchanging heat, water, carbon etc with the atmosphere

3 Surface Air Temperature Trend Annual mean relative to average Global mean surface air temperature Global-mean surface air T

4 Update

5 Where is the heat coming from? Incoming Solar Radiation Outgoing Earth Radiation Two possibilities: 1. Radiative imbalance at the top of the atmosphere 2. From the ocean.. which would therefore cool

6 Measuring heat content in the ocean How we used to do it Research ships running long hydrographic sections of temperature and salinity

7 Measuring heat content in the ocean How we do it now (2000 s onwards) Argo Array Argo float Autonomous Profiling Floats Owens, Woods Hole Oceanographic Institution Davis & Roemmich, Scripps Institute of Oceanography

8 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

9 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

10 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

11 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

12 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

13 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

14 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

15 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

16 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

17 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

18 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

19 Air-Ocean Temperatures Annual mean relative to average Surface Air Global mean surface air temperature N Ocean

20 Air-Ocean Temperatures yr 5yr 0 - surface 2kmair ocean 1km Annual means relative to average 1km (relative to this period s average) sin(latitude) S EQ N N 2km

21 Numbers (back of the envelope) Rate of change of heat content Radiative forcing Damping Climate sensitivity 0.5 o C over 1 km in 100 years λλλλ density specific heat RR H Think of a 50W bulb lighting a room of dimension 7m x 7m ~ 50m 2 Everywhere, all the time 1 W m -2 x 5.1 x m 2 = 5 x W = 500 TW (about 30 times current global energy consumption by humans)

22 Sea Level Change Implied sea-level rise due to water over 1 km warming 0.5 o C during 100yr h H Satellite era 3 mm/yr Uncertainties largely due to quantifying the land-ice contribution 10cm Courtesy of Patrick Heimbach, MIT

23 Radiative forcing Total Anthro forcing other GHG W A R M I N G Krakatoa volcanos El Chichon Pinatubo aerosols land use C O O L I N G Tambora Year 2011 Faustian bargain contract with the devil If we clean up the atmosphere, global warming may be accelerated

24 Update

25 Climate Response Functions forcing Impulse functions 4xC0 2 Global average SST response time Green s function response reveals characteristic patterns and timescales MIT Ocean circulation model

26 Anthropogenic Temperature Antarctic upwelling sinking Arctic Zonal average 0 C SST change over 100 years Arctic warms more rapidly than the Antarctic Can think of anthropogenic temperature as a passive tracer advected by ocean circulation and weakly damped at the surface at a rate set by the climate sensitivity Not always true.

27 Spatial Patterns of warming Temperature change ( C) after 100 years 5 Ocean-only MITgcm CMIP5 coupled climate models C 0 (17 models, abrupt 4xCO 2 ) Delayed warming in Southern Ocean

28 Energy accumulation, storage and transport Surface energy accumulation over 100 years Energy (J x ) Ocean temperature change over 100 years 3 Depth (m) Anomalous Heat transport PW 0 60S c o o l i n g 30S Eq Latitude 30N Anomalous Heat transport 60N w a r m i n g C 0 2 1

29 Thinning Ice in the Arctic 10 5 km 2 Northwest Passage surface area Multi-Year Sea Ice Cover yr Arctic ice cap has been thinning, opening up new shipping lanes: access to oil and gas fields, minerals, fishing in international waters

30 Thinning Ice in the Arctic Patrick Heimbach, MIT Dimitris Menemenlic JPL

31 Sea-ice trends Arctic National Snow and Ice Data Center, Boulder average Antarctic average

32 update

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34 Antarctic SST and sea-ice trends last 30 years Southern Ocean SST trends ( ), K/decade infrared (Reynolds 2002) Antarctic sea-ice concentration trends ( ) (standard deviations/decade) microwave, NSIDC (Comiso 2012) Maksym et al (2012) Interior Ocean temperature trend Ute Hausmann sea-ice area anomaly timeseries, by season

35 Wind trends around Antarctica Southern Ocean surface wind trends (in m/s per decade, ERA-Interim annual-mean): vectors Winter (Sep) & summer (Feb) sea-ice edge: black contours Annual-mean zero wind line: magenta contour Bathymetry: colors (in km) Westerly Wind Trends Ute Hausmann Annual-mean SAM trend

36 Conclusions what s happening and why? Gappy obs, short time-series, uneven quality. Uncertainties increase as scale decreases. But global picture fairly clear. Heat and CO 2 from atmosphere Atmosphere is warming because of increased concentrations of GHGs Oceans are warming in response to atmos change Sea level is rising Arctic ice thinning Changing ocean currents Ocean has a cooling effect on the atmosphere Hiatus periods - to be expected and not surprising Ocean is not passive, but plays an active role in setting patterns and timing of warming. Polar asymmetries Observed Change in Ocean Temperature ( ) minus ( ) Ocean is also becoming more acidic Implications for biology and biogeochemistry of the ocean.