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Tipping Points

Tipping Points. The ‘what’s new’ questions… Give me 2 questions each for the take-home exam. If present trends continue… But what about the tipping points: A slowing or collapse of the Gulf Stream The demise of the Amazon rain forest The release of gas hydrates from the sea floor.

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Tipping Points

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  1. Tipping Points

  2. The ‘what’s new’ questions… • Give me 2 questions each for the take-home exam

  3. If present trends continue… • But what about the tipping points: • A slowing or collapse of the Gulf Stream • The demise of the Amazon rain forest • The release of gas hydrates from the sea floor

  4. What are the chances of the Gulf Stream shutting down this century? • Under what conditions might it occur? • What would be the warning signs?

  5. (1): Collapse of the Gulf Stream

  6. It is the fastest ocean current in the world • It is complex • Volume of water – huge! • Ocean currents are measured in Sverdrups • 1 Sverdrup = a flow of 1 million cubic meters of water per second per square kilometer • Overall - ~ 100 Sverdrups • Northern section: Gulf stream is far warmer than the waters that surround it. • So? • “As air is 770 times as light as water, it follows that the heat from one cubic foot of water will warm more than 3000 cubic feet of air.” (Wallace, 1903) • In the north Atlantic, where the Gulf Stream releases its heat, it warms Europe’s climate as much as if the continent’s sunlight were increased by a third.

  7. History…. • 20,000 years ago: earth’s climate shifted from ice-age to mild climate of today - Gulf Stream repeatedly destabilized • ~ 8,000 years ago, another collapse. • Between 4,200 and 3,900 years ago – slowed • Why? • Vast influxes of freshwater into the north Atlantic • Freshwater disrupts the Gulf Stream because it dilutes its saltiness, preventing it from sinking, and thus disrupting the circulation of the oceans worldwide

  8. What are the chances? • Will there be a sufficient flow of freshwater? • The frozen north does have enough ice to fulfill that liquid potential • Plus – the increasing rainfall

  9. Since 1970: • The Gulf Stream has slowed by 6 million tonnes of water per second over the past 30 years. • Decrease in salinity (from 34,960 ppm to 34,900 ppm.) • it is the differential in salt content (1,900 ppm) that keeps the Gulf Stream moving • Examining the salinity of the Atlantic Ocean from Pole to Pole (1955-69 and 1985-99): • “fresh water has been lost from low latitudes and added at high latitudes, at a pace exceeding the ocean circulation’s ability to compensate.” • World’s evaporation and precipitation rates increased by 5-10%

  10. So: tropical Atlantic is getting saltier. ? • -> temporary quickening of the Gulf Stream before its abrupt shutdown • Why? • More heat transferred to the Poles  melt more ice  freshen the north Atlantic  collapsing the system

  11. How fast could it happen? • Ice cores from Greenland: as the Gulf Stream slowed in the past, the island had a 18F drop in a decade! • So: extreme changes could be felt over Europe and North America within a couple of winters if the Gulf Stream were to slow down • When? • What don’t we know for sure? • Uncertainty about the rate of melting of the ice caps • Complexity of other factors

  12. Different scenarios • “Even with immediate climate policy action, say scientists, there would still be a 25 percent probability of a collapse of the system of currents that keep western Europe warmer than regions at similar latitudes in other parts of the world.” (Schlesinger et al, 2005) • http://www.metoffice.gov.uk/corporate/pressoffice/adcc/BookCh5Jan2006.pdf (you are responsible for this paper)

  13. Flannery: by 2080, Greenland would be 7 F warmer  melt enough ice to raise sea level by 2 inches  enough Sverdrups to shut down the current for some centuries • But: • Then it would get colder  melting of Greenland’s ice halted  current would eventually restart  melting of ice restarted again • Pattern until ice reserve reaches a threshold – insufficient flow to disrupt the Gulf Stream

  14. Other scientists contend… • Chance of major disruption to the Gulf Stream this century – 5% of less (Hadley Centre in England)

  15. Readings • http://yaleglobal.yale.edu/display.article?id=2798 - Will Global Warming Trigger a New Ice Age? (Bill McGuire, 2003) • http://www.guardian.co.uk/environment/2005/dec/01/science.climatechange - Alarm over dramatic weakening of Gulf Stream (Sample, 2005) • http://science.nasa.gov/headlines/y2004/05mar_arctic.htm - A Chilling Possibility (NASA, 2004) • http://environment.newscientist.com/channel/earth/climate-change/dn12528-saltier-north-atlantic-should-give-currents-a-boost.html Saltier North Atlantic should give currents a boost (New Scientist, 2007) • http://sitemaker.umich.edu/section2group2/home - Thermohaline Circulation and the Effects of Global Warming

  16. Consequences? • You tell me…

  17. (2) Collapse of the Amazon Rain Forests • Reserve of carbon in the soil: potential source of CO2 so enormous it dwarfs the amount stored in living vegetation • This carbon is finely balanced: a small change in temperature can turn the soils from an absorber of CO2 to an emitter • How?

  18. Relationships… • Relationship of temperature to decomposition? – positive feedback loop • Hadley Centre’s vegetation model examined 5 plant categories • Broadleaf trees • Needle-leaf trees • Two principal kinds of grasses (C3 and C4) • Shrubs • What happens to the plants as CO2 increases?

  19. When scientists examined the water falling in the western Amazon Basin, they discovered it was low in 18O. Water had been recycled into the atmosphere so many times that most of the 18O had been left behind to the east. • What does this mean? • Plants of the Amazon effectively create their own rainfall • How? • Volume of water transpired by them  forms clouds -> blown westward  moisture falls as rain  transpired…

  20. How do plants transpire? • As CO2 levels increase  plants of the Amazonian rain forest will keep their stomata closed for longer  transpiration will be reduced  less rain • Hadley’s Centre: by 2100, levels of CO2 so high that Amazonian rainfall will decline dramatically, 20% of that decline due to stomata closures • Rainfall reduced from 0.2 inches/day to 0.08 inches/day by 2100; northeastern Amazon: zero rainfall • Then what?

  21. Series of positive feedback loops • By 2100, earth’s atmosphere: close to 1,000 ppm • When? – signs of rain forest collapse around 2040; by 2100, rain forest cover would have been reduced from its present 80% to < 10% • Consequences: you tell me

  22. Readings • http://news.bbc.co.uk/2/hi/americas/6484073.stm - Amazon 'faces more deadly droughts.’ BBC (2007) • http://environment.newscientist.com/channel/earth/climate-change/dn13034-peatland-destruction-is-releasing-vast-amounts-of-cosub2sub.htmlPeatland destruction is releasing vast amounts of CO2 (New Scientist, 2007) • http://environment.newscientist.com/channel/earth/climate-change/mg19626322.900-plants-do-emit-methane-after-all.html Plants do emit methane after all (New Scientist, 2007) • http://environment.newscientist.com/channel/earth/climate-change/mg19626271.900-cosub2sub-dont-count-on-the-trees.html CO2: Don't count on the trees (New Scientist, 2007) • http://www.whrc.org/resources/published_literature/pdf/Amazon-and-Climate-2006.pdf The Amazon in a Changing Climate: Large-Scale Reductions of Carbon Emissions from Deforestation and Forest Impoverishment (2007)

  23. (3) Methane Release from Sea Floor • Calthrates: structure of ice-methane combination in which ice crystals trap molecules of methane in tiny ‘cages’ • Massive volumes lie buried in the seabed: twice as much in energy terms as all other fossil fuels combined • Optimum conditions: where ocean water is more than 1,300 feet deep and bottom temperatures are below 34-35 F • What keeps it solid? • Only the pressure of the overlying water and the cold • Very large volumes also found in the Arctic Ocean

  24. If pressure on clathrates decreases… • If temperature of deep oceans increases… • Colossal amounts of methane could be released • a study of ocean sediments near California, found that during the last two major warming periods, around 11,000 and 15,000 years ago, three times more oil and methane were released than average. Researchers hypothesize that undersea methane ice melt could disturb the seafloor and open new cracks for seepage. • Consequences? • Need to also remember the methane and CO2 stored in the permafrost

  25. Readings • http://sciencenow.sciencemag.org/cgi/content/full/2006/828/1Marine Methane Heats Things Up (Science Now, 2006) • http://depsc.delaware.gov/electric/irp/tolmanpaper.pdfTHE MULTIPLE THREATS OF GLOBAL WARMING, METHANE RELEASE, AND OCEAN ACIDIFICATION (Tolman, 2006) • http://www.sciencedaily.com/releases/2003/02/030226074109.htmFossil Records Show Methane In Seafloor Sediments Released During Periods Of Rapid Climate Warming (2003)

  26. Additional Readings • http://www.climate.unsw.edu.au/bali/

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