Wednesday, March 21, 2012 CC-BY-NC
Wed, March 21

Maintainer: admin

1from last class - warming and precipitation

1.1climate change impacts - arctic

1.1.1arctic tundra

  • 10 degree summer isotherm (doesn't get above 10 degrees celcius in summer)
  • treeless
  • long winters (little sun), short growing season (very sunny - almost as sunny as it is in MTL)

1.1.2permafrost - frost over a summer

  • 4 types: alpine (largest of which in Himalayas), continuous, subsea (under ocean, formed during last glacial period, areas that weren't under water in last glacial period, now it is cold enough that it isn't really melting), discontinuous
  • permafrost isn't static - the temp changes (in some places, it is getting colder - this happens in places where the snow is melting i.e. less insulation)

1.1.3ice sheets

  • 'mass of ice that is 50,000 square killometers ... '
  • only two exist: antarctic, greenland (99% of freshwater)
  • form through accumulation of snow (just like glaciers)
  • snow builds up, it gets so big that it flows outward, keeps flowing outward until it reaches the water
  • thickness! greenland: 1.6 km, antarctic: 4.5 km max
  • sea level rise if melted: greenland - 6m, antarctic - 20m regions
  • lack trees
  • permafrost
  • similar to arctic tundra
  • small ice sheet
  • difference between glaciar and perennial snow field - glacier is much heavier, snow is compreseed into ice, and the pressure/mass causes it to flow (like a fluid) downhill
  • several features: accumulation zone (top): increase of mass, it flows downhill. ablation zone: more melting than gaining of snow. equilibrium point: melting matches ice movement
  • glacier transportation of materials: at top: plucking (not much mass at the top, just picking up stuff)
  • glacier movement: drag - movement at the bottom is moving slower than at the top - forms crevasses

1.2climate change effects

  • interested in number of freezing/melting days (increasing: chart from alaksa weather station)
  • interested in changes of snow pack (animals ability to hibernate)

1.3energy budgets in the poles

  • 90% of energy bouncing back: snow (the rest goes to melting the snow)
  • 20-30%: soil (the rest goes to heating the air)
  • 10-60%: water (the rest goes to heating the water)

1.4melting the permafrost

  • Seward Peninsula in Alaska
  • consquences: local (erosion)
  • affects tundra: ice to water, ice has bigger volume than water (by 10%) so the landscape subsides, effects hydrology
  • ecosystems rely on permafrast: drunken trees - trees anchor to permafrost, water in ecosystems - dry to wet + water cycles.. big disturbance to ecosystem, fire - increases flammability of forest
  • foundation of buildings crumble (oil + gas infrastructure - oil pipelines)
  • artic regions are very wet in summer - to access regions is to drive on ice in the winter - w/decrease in length of winter, duration of ice roads in Alaska have decreased by 50% (50% less time for resource extraction)
  • most important: things are stored in permafrost: 700 gigatons of carbon (1-2 times of all carbon in atmosophere), when it melts, it becomes active, microrobes release carbon into air. also huge methane stores in subsea permafrost
  • as permafrost melts, becomes wetter, so anaerobic respiration, so more co2

1.5sea ice in the arctic

  • total decrease of ice in arctic ocean: ~50% decrease 1979 - 2007 (- decrease 7 million to 4 million square kilometers
  • could send ships through arctic
  • changes albedo -> positive feedback
  • ice is unstable and will break up - may end up blocking current shipping lanes

  • appears to be melting faster than we expect - feedback loop is stronger than expected

  • navy says that the ice is thinning
  • polar bears - hang out on the ice - either get trapped or are limited to fishing on the land
  • melting ice -> highly productive ocean (nutrients get released from ice). productive zone moves with the ice melting moving - ecosystem is tightly coupled to this. if no more ice melting, then no more fisheries
  • mining + oil: opportunities in the sea floor that is being melted
  • (note, melting of ice doesn't affect sea level)

1.6how to glaciers melt

  • melts of the end - slow gradual melting
  • sudden melting events: melting on the surface -> pools of water -> lakes start to melt downwards -> forming a tunnel and a river through the glacier -> weak point as well as a lubricated layer for the glacier to move really quickly on ('moulin')
  • 1/3rd surface and end melting, 2/3rd glacier melting off and moving into the sea (moulin)

1.7quantifying the change of melting

  • changes of gravity due to melting: Nature paper: himalyas aren't melting, but Patagonia is melting quickly. from glaciers, mass loss rate of 148 gigatons of ice left glaciers and went into the oceans +/- 30 gigatons. contributes to 0.4mm sea level riseper year. from ice sheets, 1.06 mm/year (paper looked at every single glacier, quantitatively!)

1.8larson b ice shelf

  • 3,200 square kilometers of ice slid into ocean
  • melting from moulins
  • without this ice shelf, an abrupt movement of ice into the ocean - now an order of magnitude more ice sliding into ocean

1.9movie: effect of melting glaciers in the Himalayas - glacial lake outbursts floods

  • melting glacier into a lake could overflow the lake and cause a 'silent tsunami', destroying mountain villages
  • some lakes are at different lattitudes, and are sepparated by a natural dam (a moraine). if the upper lake rises from glaciar melting, then the natural dam could break

1.10ice sheets - greenland

  • surface elevation vs ice thickness - surface elevation goes down in the thickest places, because the ice is so heavy, it pushes it into the land
  • as ice melts, there will be some rebound in the land from the released pressure
  • greenland - melting towards edges, gaining towards the center (melting is not uniform!)
  • predictions when the greeland ice sheet will melt: melting of the ice sheet of greeland won't happen for thousands of years (i.e. not really a concern for us)

1.11contribution of sea level rise

  • most of it is within the small glaciers and ice caps

1.12sea level rise

  • erosion near costal communities
  • flooding of costal communities
  • in canada: land is still rebounding from the previous ice age - the rate of rebounding is as fast as the rise in sea level
  • but tropical areas where the land isn't rebounded, there will be trouble in 500-700 yrs