Global Warming

Understanding the essential properties of water helps us understand the effect of global warming.

Arctic Ice Sheet
  • North Pole, floating
  • summer area = 5,000,000 km^3
  • winter area = 10,000,000 km^3
  • thickness = 3-4 m
  • average volume = 20,000 km^3
  • main problem: positive feedback
  • Wikipedia: Polar Ice Packs
Antarctic Ice Sheet
  • South Pole, on land
  • area = 14,000,000 km^2
  • average thickness = 2000 m
  • maximum thickness = 4500 m
  • volume = 30,000,000 km^3
  • main problem: sea level rise

Questions to Consider: Sea Level Rise

  1. Consider an ice cube melting in a glass of water.
  2. Look at the map of the Arctic Ocean.
  3. Look at the map of Antarctica.
  4. If the Antarctic ice cap melts, the volume of water contained in that cap will spread out over the world's ocean in a thin layer. Use dimensional analysis to write an equation that relates the volume of water, the surface area of the ocean, and the depth of the layer.

  5. Sea Level Rise: the easy way. Use the volume of the Antarctic ice sheet and the surface area of the world ocean (360,000,000 km^2), to estimate how much sea level will rise when the Antarctic ice sheet melts.

  6. Sea Level Rise: the easier way. Knowing that the oceans are 4,000 m deep and that 2% of the earth's water is contained in glaciers on land (mostly Antarctica), esitmate the amount of sea level rise whent the glaciers melt.

Current Research

We can make rough estimates of sea level rise, enough to know that mountianous regions won't be flooded. Precise estimates require a lot of careful thought about thermal expansion of water, post-glacial rebound, changing precipitation patterns and the like. A few things seem clear, however.

Within 100 years, if we don't make any changes to our lifestyles:

Does a 1 m sea level rise sound like a big deal? It's certainly not the apocalyptic vision of drowned cities, skyskrapers as islands. But think of Venice - people using the canals to get to their front doors. Or the Maldives, a nation in the Indian Ocean that could disappear completely. Closer to home, we'd definitely see some flooding in coastal cities like Miami and New York. And your beach trip to the Outer Banks? Forget it. Here is a map from the EPA, showing coastal elevations in the Carolinas .

Questions to Consider: Energy of Melting and Warming

Albedo is a measure of how much light something reflects. Positive feedback means if something starts happening (like ice melting), it changes conditions so that it happens faster and faster.
  1. Arctic Ice Sheet
  2. Antarctic Ice Sheet
  3. Comparison: Will the Arctic or Antarctic Ice sheet experience positive feedback if it starts to melt?

  4. Time to melt each ice cap
  5. One m^3 of ice weighs 1000,000 g; one km^3 of ice weighs 10^(15)g.
    Latent heat of melting ice = 80 cal/g, heat capacity of water = 1 cal/g/degree.
  6. The United States uses about 100 Quadrillion BTU's of energy each year, or 100 x 252 x 10^(15) calories. Is that greater or less than the amount of energy you calculated above?