Greenland ice melt

Ben Lee

EPS 131

Friday 10/28/2005

Overview:

• Ice melt mechanism

• Past trends

• Recent developments

• Implications

• Natural or anthropogenic?

What happens as ice melts

• Ice melt flows down to bedrock through crevasses and moulins (large tunnels)

• Water between bedrock and ice sheet acts as lubricant

• Allows ice sheet to move faster toward the coastline

• Ice movement-rate increases from 31.3 cm (12.3 inches) per day in winter to 40 cm (15.7 inches) per day in the summer.

• It was initially thought to occur only under small mountain glaciers, not large ice sheets.

NASA P-3B

Laser altimeter + GPS

• Knowing the position and altitude of aircraft and speed of laser allows for the precise calculation of ice sheet elevation.

• Spans an area of about 650 feet wide below aircraft.

• Accuracy within 10 cm.

• Thinning along the coast leading to a rise of sea level of 0.25 mm per year.

• Thickening in Southeast Greenland by about a meter between 2002 and 2003.

• Recent paper in Science [Johannessen et al., 2005] found an increase in ice sheet height of 6.4 +/- 0.2 cm per year above 1500 m elevation.

Implications

• A 25 cm decrease in average height of central Greenland ice sheet would result in a 1 mm increase in the sea level of the world’s oceans.

• A complete melt would result in an increase in the world’s sea level by 7 m.

• Loss of lives, destruction to property and ecosystems, as well as extinction of many species.

• Positive feedbacks

• Weaken or disrupt the thermohaline circulation??

• Benefits???

Natural or Anthropogenic???

• Is the melting part of a natural cycle?Are we entering a natural warming period?Could it be due to large-scale atmospheric circulation (i.e. Arctic Oscillation)?

• Is the melting anthropogenically induced? Global warming from greenhouse gases?

Abdalati, W. and K. Steffen (2001), Greenland ice sheet melt extent: 1979-1999, J. Geophys. Res., 106(D24), 33,983-33,989

Johannessen, O. M., K. Khvorostovsky, M. W. Miles and L. P. Bobylev, Recent Ice-Sheet Growth in the Interior of Greenland, Published online October 20 2005; 10.1126/science.1115356 (Science Express Reports)

National Aeronautics and Space Administration, http://www.nasa.gov

Krabill, W., E. Hanna, P. Huybrechts, W. Abdalati, J. Cappelen, B. Csatho, E. Frederick, S. Manizade, C. Martin, J. Sonntag, R. Swift, R. Thomas and J. Yungel (2004), Greenland Ice Sheet: Increased coastal thinning, Geophys. Res. Lett., 31, L24402, doi:10.1029/2004GL021533

Krabill, W., R. Thomas, K. Jezek, K. Kuivinen and S. Manizade (1995), Greenland ice sheet thickness changes measured by laser altimetry, Geophys. Res. Lett., 22(17), 2341-2344

National Snow and Ice Data Center, http://nsidc.org

References