Future Climate and Sea Level

Transcription

1 Future Climate and Sea Level

2 Tonight: 2 nd night on human changes and controversy around them. three night series : 1) An Inconvenient truth 2) Impacts: Observed Warming and Projected Sea Level Changes 3) The Climate Hoax and discussion (next tues)

3 Outline for tonight 1) Current Warming 2) Sea Level Rise basis, observations, predictions 3) Future Warming- Models and uncertainties

4 Reprise: High levels of greenhouse gases due to human activity

5 Reprise: all these greenhouse gasses correlate with warm periods in proxy records. They are key feedback amplifiers when they are part of natural ice age cycles.

6 Recall: Radiative forcing Source: IPCC Working Group I Fourth Assessment Report Summary for Policymakers.Author: Leland McInnes.

7 Based on increases in greenhouse gasses alone*, you would predict that average global temperatures should start going up. But are they? *unless other feedbacks cancels out their effect

8 1. Observed Warming What are observations of global temperatures?

9 The Land and Oceans have warmed

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11 Land areas are projected to warm more than the oceans with the greatest warming at high latitudes Annual mean temperature change, 2071 to 2100 relative to 1990: Global Average in 2085 = 3.1 o C

12 Problems with temperature records? 1) Complications: - thermometer records can be trickyespecially for older data Urban Heat Island effect concrete is hotter than natural areas Many long temp records come from cities

13 The latest- Oct 2011: picked up by all major newspapers

14 * Very Large study, Fund in part by Koch Brothers (major political conservative foundation) *goal: specially to look at possible bias in temp records Led by physicist at Laurcence Berkeley labs who some have labeled a skeptic Got same answer as before: temp increase of ~ 1 degree globally since Involved scientists with expertise in looking at/ correcting physical data bias

15 Drought and Floods? 2) Global Precipitation patterns

16 Basic Hydrologic Cycle What is effect of increased global temperature?

17 Warmer temps => rev up hydrologic cycle More heat on planet= more evaporation = overall more rain But where? When?

18 Recall : Major circulation cells global moisture bands Warm rising air WIND LOW Pressure Equator WIND Cold sinking air HIGH Pressure 30? N

19 Precipitation patterns have also changed

20 Some areas are projected to become wetter, others drier with an overall increase projected Annual mean precipitation change: 2071 to 2100 Relative to 1990

21 Could this mean LESS water problems overall? BUT: many offsetting effects: Snowmelt earlier, less snow pack (less natural storage) Seawater intrusion to aquifers- removes part of key source Increased variability? (makes storage harder?- may make some of fresh water increase is unusable, if it comes only in relatively rare extreme events) Note: outcome for people depends a LOT on where pop growth occurs The A2 difference is due to heterogeneous population- assume all in cities, but does not specify

22 Drought Severity Index: suggests changes in regularity of rain may offset overall increase in global rain

23 Summary of Observed Climate Changes Temperature increase over last 100 years was about 0.7 C globally All latitudes and seasons Both hemispheres Land and Ocean More at high NH latitudes A few spots where it has cooled or stayed the same Warming was not steady, cooling in the 1940 s s Arctic sea ice and NH snow cover has decreased ~2% increase in precipitation globally Observed Sea Level Change 3 mm/year, but it looks like rate has been increasing!

24 Lights please..

25 Sea Level Changes First: a primer on COASTAL SEA LEVEL CHANGE

26 Two types 1. Eustatic (= Global - the same everywhere) Caused by ocean warming (thermal heat expansion) - Changes in the ice sheet size (which changes the amount of water stored on land)

27 Example: Eustatic Change due to Ice Sheet growth/melt Ice Sheet Melts ICE SHEET Sea Level Rises Continent Ocean Ocean crust Continent

28 Eustatic Sea Level Change due to Global Warming Ocean Warms and expands Sea Level Rises Continent Ocean Ocean crust Continent

29 Type #2: relative 2. Relative (Due to local tectonics) Sediment loading on shelf sea level rises Mantle rebound from ice sheet melting sea level drops Active margin - uplift land sea level drops

30 Relative Sea Level Change due to Sediment Loading on Shelf As sediment load increases Shelf subsides Relative Sea Level Rise X X Continental Shelf Ocean

31 Relative Sea Level Change due to Mantle Rebound Ice Sheets Depressed mantle under continental crust X Mantle Rebounds Relative Sea Level Ice Lowering Sheet Melts Sea Level Rises X Continental Shelf Ocean

32 Recall: on geologic timescales, sea level fluctuates Greatly (Coastlines are rarely in equilibrium ) Major swings in sea level up to 125 meters (300+ feet!)! Sea level back in time Note: we are now at a relatively high sea level time. ( Mostly due to being between ice age cycles)

33 Features from sea level drop / tectonic uplift Ancient terraces Features from sea level rise

34 OUR coast: Tectonic uplift has been much faster than sea level rise during recent time Scruz terrace series

35 Terraces are remarkably obvious if you drive up HWY 1 Scruz terrace series

36 Terraces are remarkably obvious if you drive up HWY 1 Scruz terrace series

37 TODAY - Eustatic Sea Level Rise Causes Coastal Erosion Everywhere - but especially Passive Margins-(no uplift) Recap: Sea level rise today

38 Todays Sea Level Change What are some sources (drivers)?

39 Ocean thermal expansion Currently responsible for 1.6 mm/year of sea level rise Rising temperatures decrease the density of seawater and increase in its volume. A rise in sea level is the only way the oceans can adjust to this change in volume

40 Melting of Alpine Glaciers Currently responsible for 0.77 mm/year of sea level rise Mount Kilimanjaro February 17, 1993 February 20, 2000 Ice fields on Africa's highest mountain shrank by 80 percent in the past century. Snow cap of Mount Kilimanjaro will be gone in two decades.

41 Greenland Ice Sheet Melting Currently responsible for 0.21 mm/year of sea level rise A record maximum melt extent on the Greenland ice sheet in 2002 Since 2000: rate of melting has increased

42 RATES: Observed Sea Level Change Rate of sea level rise has been increasing (currently ~3 mm/year)

43 Overall: current trends EAST Coast: Eustatic sea level rise (due to global warming) Sediment loading on shelf pushing down sea level rise At this moment Total = fast sea level rise about 1 foot per century.

44 Overall-current trends: WEST COAST: Eustatic sea level rise (due to global warming) Tectonic uplift = sea level drop Total = ~ probably very slow sea level rise Overall: on average, relatively slower erosion than east

45 Recall: we are currently in warm period already- so current trends are TINY compared to geological cycles BUT.. Will they stay that way? Major swings in sea level up to 125 meters (300+ feet!)! Sea level back in time Note: we are now at a relatively high sea level time. ( Mostly due to being between ice age cycles)

46 Possible sources for ultimate Sea Level Change 1) Ocean thermal heat expansion: moderate effect, high certainty 3) Changes to water stored on land (rivers/lakes/groundwater): minor effect 2) Changes to cryosphere: possible huge Short term effects of global warming Alpine glaciers and small ice caps melting (contain water to change sea level by 51 cm) moderate effect, high certainty Greenland ice sheet (contains water to change sea level by 7.20 m ~ 20 feet feet) HUGE EFFECT moderate certainty Antarctic ice sheet (whole thing- contains water to change sea level by m = ~ 180 feet) Killer..catastrophic effect..ice age flux scale- high uncertainty Long term effects of natural deglaciation - minor effect

47 Possible sources for ultimate Sea Level Change 2) Changes to cryosphere: Short term effects of global warming Alpine glaciers and small ice caps melting (contain water to change sea level by 51 cm) moderate effect, high certainty Greenland ice sheet (contains water to change sea level by 7.20 m ~ 20 feet feet) HUGE EFFECT moderate certainty Antarctic ice sheet (whole thing- contains water to change sea level by m = ~ 180 feet) Killer..catastrophic effect..ice age flux scale- high uncertainty Long term effects of natural deglaciation - minor effect

48 4. Sea Level Predictions?

49 Greenland Ice Sheet Melting: Model Predictions

50 Predicted Changes in Sea Level due to Thermal Expansion of the Oceans

51 Sea Level Predictions for

52 Greenland ice sheet contains water equivalent to 7.2 m of sea level rise.

53 Total Greenland ice sheet contains water equivalent to 7.2 m of sea level rise.

54 Maldives and other island nations will be influenced by even small changes in sea level