Geo 105, Main points for temperature for Feb 10

Observations of temperature on Earth

• Variations at all "times scales"
  • Daily variations are very large
  • Seasonal variations of daily average can be very large at many places
    e.g., a mid-latitude continental site like Michigan
  • Annual variations , at a single spot, are large
  • Annual variations , average over a large region, are small To compare variations across large regions, should look at the the differences in annual average temperatures, then
  • Annual variations over the Earth seem to suggest "global warming" in past hundred years or so, but variations are small
  • Variations over millions of years, (oceanic sediments), the variations are tiny if you consider that they slowly change by tens of degrees over millions of years. But, some suggestion that Earth was warmer back in Cretaceous.

What do we expect the temp of Earth to be?

• "First-order" answer is the idealized black-body calculation, where the Earth radiates away, as a uniform black sphere, the incoming solar energy. Gives a reasonable estimate.
• But if we reflect away 30% of incoming energy, due to clouds & ice, then temperature is much colder.
• But, Earth can not instantly transfer all the energy to ensure a uniform temperature
• Due to spherical shape, the equatorial region receives its full share of solar energy, while the polar regions have much less incoming energy. Thus, a solid Earth would be cool at the equator, and incredibly cold in the polar regions!