A View from the Back of the Envelope top

Earth's surface as a
20 x 25 Megameter rectangle
Area
The relative size of Earth, Jupiter, Sun

The idea: You can think of Earth's surface as a 20x25 Mm rectangle. A surface area of 500 square Megameters. Sketching areas of interest on graph paper (land vs sea, assorted continents, sky clear/clouded/stormy, etc) is a nice way to get a feel for them.

Earth's surface area is 500 Mm2

Well, it's actually 510 Mm^2, not 500.
A -2% approximation error.
That's 10 missing squares.

Ecosystems example

                   Earth

  20 9 8 7 6 5 4 3 2 110 9 8 7 6 5 4 3 2 1   Mm  MegaMeter  10^6 m  1,000,000 meters
 1 o o o o o o o o o o|o o o o o o o o o o      ~600 miles           1000 km
 2 o o o o o o o o o o|o o o o o o o o o o
 3 o o o o o o o o o o|o o o o o o o o o o   Each letter is a square Megameter  Mm^2
 4 o o o o o o o o o o|o o o o o o o o o o
 5 o o o o o o o o o o|o o o o o o o o o o
 6 o o o o o o o o o o|o o o o o o o o o o
 7 o o o o o o o o o o|o o o o o o o o o o         Productivity color code
 8 o o o o o o o o o o|o o o o o o o o o o             Most, less, little
 9 o o o o o o o o o o|o o o o o o o o o o
10 o o o o o o o o o o|o o o o o o o o o o
11 o o o o o o o o o o|o o o o o o o o o o
12 o o o o o o o o o o|o o o o o o o o o o   open ocean        (332 Mm^2)
13 o o o o o o o o o o|o o o \ \ \ \ \ \ \   continental shelf  (27 Mm^2)
14 o o o o o o o o o o|o o \ \ M M E R l l   Marsh/swamp, Estuary, Reef/algal-bed; lake
15 o o o o o o o o o o|o \ n n n n n n n n   tundra & alpine meadow (8 Mm^2)
16 o o o o o o o o o o|\ \ w w w w w w w w   wood/shrubland     (8 Mm^2)
17 o o o o o o o o \ \|\ g g g g g g g g g   grassland          (9 Mm^2)
18 o o o o o o o \ b b|b b b b b b b b b b   boreal forest      (12 Mm^2)
19 o o o o o o o \ t t|t t t t t t t t t t   temperate forest   (12 Mm^2)
20 o o o o o o o \ T T|T T T T T T T T T T   Tropical  forest   (25 Mm^2)
21 o o o o o o \ \ T T|T T T T T T T T T T   Tropical  forest
22 o o o o o \ % % % %|% % % % % % % % % %   cultivated         (14 Mm^2)
23 \ \ \ \ \ s s s s s|s s s s s s s s s s   savanna            (15 Mm^2)
24 - - - d d d d d d d|d d d d d d d d d d   desert scrub       (18 Mm^2)  [total        ]
25 - - - - - - - - - -|- - - - - - - - - -   ice, sand & rock   (24 Mm^2)  [land 148 Mm^2]

Links
Biomes
Major Biomes of the World
The World's Biomes
Tour of Biomes
Biomes of the World

A View from the Back of the Envelope
Comments encouraged. - Mitchell N Charity <mcharity@lcs.mit.edu>

Notes:
  1 Mm^2 = 10^6 km^2 =~ 400,000 mile^2 (statute miles, not nautical)
Data for the grid above...
 ecosystem type       area        average net primary
                   (10^12 m^2)   productivity (kg(C)/m^2/yr)
  tropical forests       24.5         0.83
 temperate forests       12.0         0.56
    boreal forests       12.0         0.36
 woodland and shrubland   8.0         0.27
 savanna                 15.0         0.32
 grassland                9.0         0.23
 tundra and alpine meadow 8.0         0.065
 desert scrub            18.0         0.032
 rock, ice, and sand     24.0         0.015
 cultivated land         14.0         0.29
 swamp and marsh          2.0         1.13
 lake and stream          2.5         0.23
 open ocean             332.0         0.057
 upwelling zones          0.4         0.23
 continental shelf       26.6         0.16
 algal bed and reef       0.6         0.90
 estuaries                1.4         0.81
  [From Consider a Spherical Cow, pg 257]
There is a version sorted by npp here (near the bottom).
Doables:
  Say the words "graph paper".
  Point out richness of biome graph.
  Discuss tradeoffs on size, shape, arrangement.  Extra ten line.
  Exercises section -
   on a blank 20x25 grid, draw boxes for Earth's continents.
   land/sea, clear/cloud/storm, insolation, 
   Include links to data for exercises.
  On biome grid
    sketch productivities.
    `The sea is a desert (productivity-wise), but there is a lot of it. (x10)'
    describe errors?
  Point out percentages (100Mmsq-20%, etc).

History:
  2003-Feb-03  Fixed links - 1 repaired, 3 removed.
  1999.Dec.14  Created page.
  1999.Dec.09  Nice biome grid.  Page sketch.
  1999.Mar.03  Play.