The oceans: Sea level rise & gulf stream

Transcription

1 Lecture Climate Change Lesson 10 The oceans: Sea level rise & gulf stream Rene Orth

2 1 Course webpage

3 Lesson 10 The oceans: Sea level rise & gulf stream 1) Arctic Sea ice 2) Sea level rise 3) Thermohaline circulation 4) Ocean acidification

4 2 Arctic Sea ice Akclimate.org Strong seasonal variations Minimum in September

5 3 Arctic Sea ice Maloney et al. (2013) Arctic could become (seasonally) ice-free Large uncertainties through model and scenario differences

6 4 Arctic Sea ice Arctic Sea ice shrinking mostly off the shore of Russia & Alaska IPCC (2013)

7 5 Also Antarctic sea ice is threatened by climate change IPCC (2013)

8 Summary Arctic sea ice extent varies seasonally with a minimum in September This minimum extent has halved in recent years compared to pre-industrial, seasonally ice-free Arctic during this century is possible

9 Lesson 10 The oceans: Sea level rise & gulf stream 1) Arctic Sea ice 2) Sea level rise 3) Thermohaline circulation 4) Ocean acidification

10 6 Past Sea level rise wikipedia.org Sea level has risen by approx. 120 m since last glacial maximum Comparatively little change in past 6000 years

11 Past Sea level rise 7 Sea level has risen by approx. 20 cm since 1900 IPCC (2013) About ¼ of this is due to thermal expansion

12 8 Past Sea level rise Sea level rise is spatially heterogenous IPCC (2013)

13 9 Past Sea level rise Sea level rise is spatially heterogenous eea.europa.eu

14 10 Past Sea level rise Why sea level rises spatially heterogenous - changes in surface winds (North Pacific, North Atlantic) - post-glacial rebounds (Scandinavia, Canada) - tectonics (subsidence off the coast of South America) - changes in the Earth s gravity field (through ice melting) - local effects (groundwater or gas extraction)

15 11 Past Sea level rise Local effects (groundwater or gas extraction)

16 12 Sea level rise Hypothetic experiment: Melting of Greenland and Antarctic ice sheets IPCC (2013) Less sea level increase close to melting areas due to loss of gravity

17 Summary Arctic sea ice extent varies seasonally with a minimum in September This minimum extent has halved in recent years compared to pre-industrial, seasonally ice-free Arctic during this century is possible Sea level has risen by approx. 20 cm since 1900, due to melting glaciers and ice sheets, and thermal expansion Sea level rise not spatially uniform, but impacted by localregional effects such as e.g. wind, post-glacial rebound, groundwater/gas extraction

18 13 Future Sea level rise IPCC (2013) Sea level rise projected to accelerate

19 14 Future Sea level rise IPCC (2013) Strong differences across scenarios

20 15 Future Sea level rise IPCC (2013) Updated assessment projects higher sea level rise for the same scenario

21 16 Future Sea level rise IPCC (2013) Differences across models for projecting global sea level in 2100

22 17 IPCC (2013) Future Sea level rise Temperature responds increased greenhouse gas emissions with delay of decades, sea level responds with delay of centuries Sea level rise might continue for centuries

23 18 Future Sea level rise eea.europa.eu Strongest impacts on coastal lowlands & harbour cities

24 19 Future Sea level rise IPCC (2013) Strongest impacts on coastal lowlands & harbour cities

25 20 Future Sea level rise Storm surges will threaten areas not affected in the past ucsusa.com

26 21 Future Sea level rise IPCC (2013) Millions of people potentially affected by inundation

27 Summary Arctic sea ice extent varies seasonally with a minimum in September This minimum extent has halved in recent years compared to preindustrial, seasonally ice-free Arctic during this century is possible Sea level has risen by approx. 20 cm since 1900, due to melting glaciers and ice sheets, and thermal expansion Sea level rise not spatially uniform, but impacted by local-regional effects such as e.g. wind, post-glacial rebound, groundwater/gas extraction Projected additional sea level rise of cm until 2100, and continued rise afterwards Impacts on coastal population, so far unaffected areas at risk of storm surges

28 Lesson 10 The oceans: Sea level rise & gulf stream 1) Arctic Sea ice 2) Sea level rise 3) Thermohaline circulation 4) Ocean acidification

29 22 Thermohaline circulation wikipedia.org Global conveyor belt Driven by water density differences (temperature, salinity), and rotation of the Earth (Coriolis force)

30 23 Thermohaline circulation IPCC (2013) Spatial differences in ocean salinity driven by differences in evaporation minus precipitation Spatial differences in ocean temperature driven by differences in (the incidence angle of) radiation highest at equator, lowest at poles

31 24 Gulf stream wikipedia.org Gulf stream is part of the global thermohaline circulation Gulf stream visible in sea surface temperature pattern Stream called florida stream initially, Benjamin Franklin introduced the name gulf stream, corresponding to the Gulf of Mexico

32 25 European vs. American temperatures wikipedia.org

33 26 European vs. American temperatures Europe clearly warmer than America across similar latitudes Caused by transport of heat towards Europe through (1) Gulf stream, and more importantly (2) south-westerly winds

34 Summary Arctic sea ice extent varies seasonally with a minimum in September This minimum extent has halved in recent years compared to preindustrial, seasonally ice-free Arctic during this century is possible Sea level has risen by approx. 20 cm since 1900, due to melting glaciers and ice sheets, and thermal expansion Sea level rise not spatially uniform, but impacted by local-regional effects such as e.g. wind, post-glacial rebound, groundwater/gas extraction Projected additional sea level rise of cm until 2100, and continued rise afterwards Impacts on coastal population, so far unaffected areas at risk of storm surges Gulf stream is north Atlantic branch of global thermohaline circulation driven by water density differences due to salinity and temperature anomalies

35 27 Future of thermohaline circulation IPCC (2013) Ocean s salinity and temperature changes impact strength of thermohaline circulation

36 28 Future of thermohaline circulation IPCC (2013) (Long-lasting) weakening of Gulf stream projected by climate models Collapse of Gulf stream unlikely

37 29 Imprints of thermohaline circulation IPCC (2013) Distribution of total-column anthropogenic CO2 in the ocean Most CO2 taken up in deep water formation areas

38 IPCC (2013) 30 Imprints of thermohaline circulation Additional heat from greenhouse gas-induced radiative forcing mostly taken up by shallow ocean Transport into deep ocean in deep water formation areas

39 31 Imprints of thermohaline circulation Oceans have taken up by far most of the additional heat IPCC (2013)

40 Summary Arctic sea ice extent varies seasonally with a minimum in September This minimum extent has halved in recent years compared to pre-industrial, seasonally ice-free Arctic during this century is possible Sea level has risen by approx. 20 cm since 1900, due to melting glaciers and ice sheets, and thermal expansion Sea level rise not spatially uniform, but impacted by local-regional effects such as e.g. wind, post-glacial rebound, groundwater/gas extraction Projected additional sea level rise of cm until 2100, and continued rise afterwards Impacts on coastal population, so far unaffected areas at risk of storm surges Gulf stream is north Atlantic branch of global thermohaline circulation driven by water density differences due to salinity and temperature anomalies Gulf stream and thermohaline circulation projected to weaken, collapse unlikely Thermohaline circulation controls oceanic uptake of CO2 and related additional heat, most uptake in deep water formation areas

41 Lesson 10 The oceans: Sea level rise & gulf stream 1) Arctic Sea ice 2) Sea level rise 3) Thermohaline circulation 4) Ocean acidification

42 32 Ocean acidification IPCC (2013) Atmospheric CO2 propagates into ocean water, forms carbonic acid which in turn increases H+ concentration (ph value)

43 33 Ocean acidification IPCC (2013) Decreasing ph in concert with increasing atmospheric and oceanic CO2

44 Summary Arctic sea ice extent varies seasonally with a minimum in September This minimum extent has halved in recent years compared to pre-industrial, seasonally ice-free Arctic during this century is possible Sea level has risen by approx. 20 cm since 1900, due to melting glaciers and ice sheets, and thermal expansion Sea level rise not spatially uniform, but impacted by local-regional effects such as e.g. wind, post-glacial rebound, groundwater/gas extraction Projected additional sea level rise of cm until 2100, and continued rise afterwards Impacts on coastal population, so far unaffected areas at risk of storm surges Gulf stream is north Atlantic branch of global thermohaline circulation driven by water density differences due to salinity and temperature anomalies Gulf stream and thermohaline circulation projected to weaken, collapse unlikely Thermohaline circulation controls oceanic uptake of CO 2 and related additional heat, most uptake in deep water formation areas Increased atmospheric CO2 enters ocean, forms carbonic acid and hence acidifies the ocean; nevertheless overall alkaline conditions (ph > 7) likely to persist into the future