Arctic Role in Global Climate Change

I. Arctic Role in Global Climate Change.

Polar regions incorporate important environmental thresholds, many of which are associated with water-phase changes. IPCC 2001 (Impacts p. 810)

  1. Ice-albedo feedback.
    • Glaciers.
      • Glaciation (Milankovich - see Monday's lecture notes).
      • Sea level.
    • Sea ice.
      • Productivity.
  2. Thermohaline circulation.
    • Heinrich events.
    • Dansgaard/Oeschger events.
    • Hydrologic cycle (global warming: river runoff may increase by 10-20%).
  3. Greenhouse gases.
    • Source or sink of carbon dioxide and methane dependent on hydrology, rate of decomposition of exposed peat.
      • Bogs, permafrost, clathrates.

II. Global Warming.

"Because of a variety of positive feedback mechanisms, the Arctic is likely to respond rapidly and more severely than any other area on Earth, with consequent effects on sea ice, permafrost, and hydrology." IPCC 2001 (Impacts p. 807)

III. Observed 20th Century Arctic Change.

(already close to the melting point …)

  1. Air temperatures warmed as much as 5°C.
  2. Ocean temperatures have warmed by 1°C over past 20 years, Atlantic water influence has increased.
  3. Sea ice.
    • Sea ice extent decreased 2.9%/decade from 1978-1996.
      • Ice extent in the Nordic Seas has decreased 30% over the past 130 years.
    • Sea ice has thinned by 30% in some places.
    • Later freeze up (5.8 days/100yrs), earlier break up (6.5 days/100yrs).
    • Severe coastal erosion, as much as 40m/yr along the Siberian coast (wave action, thermal abrasion).
  4. Glaciers have generally retreated (and thinned by ca. 1m/yr in some places).
  5. Snow-cover extent is reduced by 10%.
  6. Change in timing snowfall vs. ice formation.
  7. Permafrost is thawing (0.1m/yr).
    • In Alaska it costs $1.5million/km to replace roads.
    • A 2oC warming in Siberian soil temperature led to a 50% decrease in bearing capacity of frozen ground under buildings.
  8. Precipitation has increased.
  9. Productivity has increased.
    • Growing degree days have increased by 20% for agriculture and forestry.
    • Boreal forests are expanding northward at a rate of 100km/°C.
    • But locations and timing are important (geometrid moths, sea ice).

Lecture by Stephanie Pfirman, 2003.