-- CHAPTER 2 -
GLOBAL SCALE LAND- AND AQUATIC AREAS
(2-A) -
Components of the Global Surface - [1] Continental Areas, [2] Land Distribution by Elevation, [3] Fresh-Water-Covered Land, [4] Land Distribution by Vegetation Type Before Human Disturbance, [5] Land Distribution by Current Vegetation Type, [6] Biologically Productive Lands, [7] Developing-, Developed- and Transition-Nation Land Area Data, [8] Land Distribution by ClimateGo to the Table of Contents of this Area-Data Document - Go to the Home Page of this Web Site
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(2-A) - Components of the Global Surface
Components of the Earth's Surface: (Areas are in millions of km2) (la)
Area Category |Area |Comments~ ~ |References
Entire Planet |510.0|incl. Oceans|(se68H1)
Oceans~ ~ ~ ~ |361.0| ~ ~ ~ ~ ~ ~|(se92Q1), p.76
Continents~ ~ |148.9|29% of total|(se82M1) (se68H1)
Glaciated Land| 15.8|See below ~ |(se82M1)
Ice-Free Land |133.1|=148.9-15.8 |------
Ice-Free Land |130.0| ~ ~ ~ ~ ~ ~|(se78B3)
Ice-Free Land |133.6| ~ ~ ~ ~ ~ ~|(se91W1)
I. D. B.**~ ~ | 33.2| ~ ~ ~ ~ ~ ~|(se82M1)
** Inland Drainage Basins (Runoff within I.D.B. is termed "endoreic" runoff.)
Hence, land drained by rivers to oceans = (133.1 - 33.2) = 99.9 million km2 ("exoreic" runoff) (se82M1).
Comments: (se68H1) (See below) gives an "exoreic" runoff area of 99.8 million km2.
Ice-free Land Areas draining to Oceans by Continent (se68H1) (la)
Continent |106 km2|Reference
N. America| ~20.7 | (se68H1)
S. America| ~19.4 | (se68H1)
Africa~ ~ | ~19.9 | (se68H1)
Australia | ~ 5.2 | (se68H1)
Europe~ ~ | ~ 9.3 | (se68H1)
Asia~ ~ ~ | ~26.9 | (se68H1)
Totals~ ~ | 101.5 | (se68H1)
Areas are from Livingston, 1963 (se68H1)
Comments: Actual continental areas are greater than the above because closed basins (not draining to oceans) are not counted above, nor is land that is ice-covered but above sea-level.
Ice-covered land and Lands not draining to Oceans (la) (Areas are in millions of km2)
Region~ ~ ~ ~ |Area~ | Comments ~ ~ |Reference
Antarctica~ ~ | 13.0 | ice-covered~ |(se68H1)
Greenland ~ ~ |~ 2.2 | Total Area ~ |(se68H1)
Greenland ~ ~ |~ 0.34| ice-free only|(se68H1)
Closed basins | 34.2 | No runoff~ ~ |(se68H1)
+deserts~ ~ ~ |
Comments:
This leaves 39.2 (148.9 - 13.0 - 2.2 + 0.34 - 34.2 = 99.8 million km2) of ice-free land contributing runoff and water-borne sediments to oceans (se68H1).Return to Table of Contents of this Chapter 2
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[2] Land Distribution by Elevation
Land above 1000 m. elevation (about 3,300 ft.) is about 27% of the world's terrestrial surface. ((se97G2), p. 17) (la)
Land above 3000 m. elevation (about 10,000 ft.) is about 5% of the world's terrestrial surface (se97G2) (la).
Comments: 148.9 * 0.05 = 7.45 million km2 above 3000 m. Tree-lines are rarely above 3000 m., so this land is almost certainly rocks, tundra, low shrub, etc. with little if any potential for serving as cropland, grazing land or forest land.
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Dam Backwaters:
Global dam-based storage basins (backwaters) cover 400,000 km2 ((se90W1), p. 170). (la)
Comments: Since 75% of the world's dams and reservoirs have been built in the past 35 years (se90W1), the global rate of land loss to dam backwaters is 0.75 x 400,000/ 35 = 8580 km2/ year. (la)
Comments: Reservoirs are typically steep-walled - typically forested lands, but they often cover lots of flood plain that is usually cropland or urban land. The urban land loss typically gets replaced elsewhere - typically on cropland.
Lake Inventory by Continent (Encyclopedia Britannica) (Lake Areas are in units of km2) (la)
Region~ ~ |No. | Total Area
These data cover lake-sizes down to about 600 km2. If one plots total area of lakes larger than Size X vs. X, and extrapolates down to X = 0, one obtains a total (global) area of lakes + inland seas of 1.40 million km2. Data for this extrapolation are given below:
If total area of inland seas (Caspian+ Aral+ Dead = 412,000 km2) is deducted, one obtains a total global lake area of about 1.0 million km2. If the total area of lakes+ rivers+ streams is 2.2 million km2 (See estimates above.), then this implies a total area of world's rivers and streams of 1.2 million km2. (la)
Comments: The area covered by dam reservoirs (400,000 km2) is probably not included in these figures.
Lakes, rivers and streams occupy 1.7% as much area as (ice-free?) land does (se77B2).
Comments: 1.7% of 130 million km2 = 2.2 million km2. (la)
(se90W1), p.123, concludes that the total area of lakes, rivers and streams = 2.0 to 3.2 million km2. (la)
Lake Victoria, the world's second-largest freshwater lake (27,000 miles2) (70,000 km2), (20% of the world's freshwater supply), is being filled in by nutrients carried in soil from deforested land. (11/4/99 Nando Times). (la) Comments: Is this lake in Africa?
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[4] Land Distribution by Vegetation Type Before Human Disturbance
World's Vegetation, prior to Historically Widespread Human Disturbance (se35J1) (la)
Land~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | Land Area
Category~ ~ ~ ~ ~ ~ ~ ~ ~ | % (Million km2 )
Tropical forests~ ~ ~ ~ ~ | 13 ( 19.4)
Boreal forests~ ~ ~ ~ ~ ~ | ~9 ( 13.4)
Mid-latitude mixed forests| ~7 ( 10.4)
Mediterranean scrub forest| ~1 (~ 1.5)
Grasslands (semi-arid?) ~ | 19 ( 28.3)
Dryland (arid+ hyperarid?)| 17 ( 25.3)
Mountains ~ ~ ~ ~ ~ ~ ~ ~ | 18 ( 26.8)
Polar ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 16 ( 23.8)
Total ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ |100 (148.9)
Comments: 100% includes ice-covered lands.
(Total is 30% forest+ 19% grassland+ 51% unproductive (last 3 categories))
Comments: Other data give only about 16 million km2 of ice-covered land, so "Polar" above may include some land that is not ice-covered - such as tundra.
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[5] Land Distribution by Current Vegetation Type
Vegetated Surface area of the Earth: 117 million km2 (og95D2). Comments: Apparently this definition includes lands too cold to grow even one crop (e.g. tundra), since most discussions of reasonably biologically productive land consider only about 85-90 million km2 of the Earth's 131 million km2 of ice-free land to fall into this category -- and this includes about 4.7 million km2 of urban land. Part of the difference between 131 million km2 of ice-free land and 117 million km2 of vegetated land is accounted for by 6 million km2 of hyper-arid land. Another part is rock, e.g. on mountaintops.
The global area of tundra is reported to be 8.8 million km2 (se82P2).
Global Biomass Inventory Around 1950 (Ref. 23 of (og78W1)) (Ref. 7 of (og77B1)) ((og90W1), p. 123)
(Areas are in millions of km2) (Plant carbon masses are in Gt.)
Comments:
The area of ice-free land is usually given as about 131 million km2 , suggesting that the area of ice-covered land is about 149-131 = 18 million km2 . The area given above for the "rock-ice-sand" ecosystem type, 24.0 million km2, thus suggests that the area of (rock + sand) to be 6 million km2. However the area of hyper-arid land (i.e. sand) is usually taken as about 6 million km2. This then leaves no land area for the land classification "rock" (which might include alpine meadows). This suggests that the area categorized as grasslands ought to be smaller than the 58.5 million km2 given in the table above.Land areas containing Various Categories of Vegetation (se82P2) (la) (Areas are in millions of km2 )
Life-Zone~ ~ ~ ~ ~ ~ ~ ~ | Land
Group~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | Area
Tropical Forest, wet ~ ~ | ~4.1 (See (4-B)[3])
Tropical Forest, moist ~ | ~5.3 (See (4-B)[3])
Tropical Forest, dry ~ ~ | ~2.4 (see (4-B)[3])
Tropical Forest, very dry| ~3.6 (See (4-B)[3])
Temperate Forest, warm ~ | ~8.6
Temperate Forest, cool ~ | ~3.4
Boreal Forest, wet ~ ~ ~ | ~6.9 (See (4-B)[2])
Boreal Forest, moist ~ ~ | ~4.2 (See (4-B)[2])
Trop. Woodlands, Savanna | 24.0
Temperate Thorn Steppe ~ | ~3.9
Cool Temperate Steppe~ ~ | ~9.0
Tropical Desert Bush ~ ~ | ~1.2
Warm Desert~ ~ ~ ~ ~ ~ ~ | 14.0
Cool Desert~ ~ ~ ~ ~ ~ ~ | ~4.2
Boreal Desert~ ~ ~ ~ ~ ~ | ~2.0
Tundra ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~8.8
Cultivated Lands ~ ~ ~ ~ | 21.2
Wetlands ~ ~ ~ ~ ~ ~ ~ ~ | ~2.8 (See (9-B)[2])
Lakes and streams~ ~ ~ ~ | ~3.2
Global Total ~ ~ ~ ~ ~ ~ |132.8
Land Areas Occupied by various categories of Plant Species (Areas (Col. 2, 3, 4) are in millions of km2 )
FAO's 1986 tabulation of global land-use (se90B1): (la)
Comments: This final figure neglects ice-covered areas such as Antarctica (13 million km2) and 2.2 million-0.34 million = 1.9 million km2 of Greenland.
Comments: Savannas, which some people believe to have been entirely converted from tropical forests, cover a global area of 15 million km2
(df79S1). (la) Open forests are generally believed to cover about 10 million km2.
The usually accepted figure for total land area (including ice covered land) is 148.9 million km2. If these percentages are converted to a total-land-area basis, the 1986 FAO data changes to:
Comments: 2% of the Earth's landmass is wetland (swamps, marshlands, bogs, etc.) (Section (se3-C)). A table in Section (se3-C) gives 4-6 million km2 of swamps, marshes, bogs, peat lands, lakes and streams. Where does this fit into the above breakdown?
Land converted to agriculture and urban or built-up areas | 38 of the 131 million km2 of ice-free land [(se00W1)?].
Land to Croplands and "managed" pastures ~ ~ ~ ~ ~ ~ ~ | 33 million km2
((se00W1), p. 24).
Comments: Apparently "managed pastures" excludes rangeland, since total grazing land includes about 32 million km2. The above numbers come from satellite data and the PAGE analysis ((se00W1), p. 52).
Comments: Since Croplands + "Managed" pastures total 33 million, and Cropland area is about 15 million km2 this appears to indicate an inventory of "Managed Pasture" of 18 million km2
.
Urban or built-up areas~ | ~4.74 million km2 [(se00W1), p. 24]. (See Chapter 7).
Land in agriculture based on national production statistics | 48.5 million km2
(FAO (se00F1)).
Comments: Apparently here the FAO counts all permanent pasture -- including rangeland. (la)
Comments: Since global cropland area is about 15 million km2 , managed pastures + rangeland must be (48.5 - 15) = 33.5 million km2
.
Four major ecological zones of tropical climates are savannas and associated grasslands (49%), evergreen forests (24%), desert (16%), and semi-desert (11%) ((se75S1), Ref. 16) (la). (Total area of land with tropical climates = ?)
Land Use in China -- Areas are in millions of km2
(and in %) (Ref. 2 of (se82B2)) (la)
Comments:
The area of deserts and the area of urban land (cities) in China have been increasing significantly in recent decades, so the above data from around 1980 is probably somewhat obsolete. (See Chapter 6, Section (6-B), "Hyper-arid Lands and Deserts".Return to Table of Contents of this Chapter 2 - Go to Table of Contents of this Document
[6] Biologically Productive Lands
Vegetated Surface area of the Earth:
117 million km2 (se95D3).
Comments: Apparently this definition includes lands too cold to grow even one crop, since most discussions of reasonably biologically productive land consider only about 85-90 million km2 of the Earth's 131 million km2
of ice-free land to fall into this category, and this includes about 4.745 million km2 (se00W1) of developed (urban) land. (la)
87.35 million km2 of land worldwide are being used for permanent and annual crops and permanent pasture or being maintained as forest and woodland (Ref. 16 of (se97C1)) (UNFAO data, 1990).
Comments: 87.35 million is something on the order of the amount of the world's reasonably biologically productive land. Adding urban lands + wetlands would give 93.35 million km2 for the amount of reasonably biologically productive land in the world. The 87.35 million km2
figure suggests a biologically non-productive area of (131- 87.35 = 43.65 million km2. (la)
43.2 million km2 of the earth's 131 million km2 of ice-free land is desert, wastelands and urban areas (se90B1). Comments:
This would suggest that 131-43 = 88 million km2 are reasonably biologically productive land.
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[7] Developing-, Developed- and Transition-Nation Land Area Data
Land Use and Population (Developing vs. Developed Countries) (ice-free land only) (la)
(Developing Countries in Col. 2; Developed Countries in Col. 3) (Ref. 3 of (se82D1))
(* millions of km2)~ ~ ~ ~ ~ |Col.2|Col.3| Total
Land Area *~ ~ ~ ~ ~ ~ ~ ~ ~ |76.19|57.73|133.92
Percent of World's Total ~ ~ |~ 57%|~ 43%|~ 100%
Population (1979) (millions) | 3117| 1218| ~4335
Percent of World's Total ~ ~ | ~72%| ~28%| ~100%
Potentially Cultivable Land *|21.54| 8.77| 30.31
Percent of Land Area ~ ~ ~ ~ | ~ 28| ~ 15| ~ ~22
Percent of World's Potential |~ 71%|~ 29%|~ 100%
Presently Cultivated Land~ * | 7.84| 6.77| 14.61
Percent of Potential ~ ~ ~ ~ | ~36%| ~77%| ~ 48%
Persons/ km2 now cultivated~ | ~400| ~180| ~ 300
Land Use and Population Data in Developing Countries
(Ref. 2 of (se82D1)) (la)Return to Table of Contents of this Chapter 2 - Go to Table of Contents of this Document
[8] Land Distribution by Climate
The total land area of 5 tropical regions is categorized by climate (Ref. (se90W1) Table 18.6 (p. 287)) (Areas are in units of 1000 km2); (la)
Region ~ ~ |Total| Arid |Semi-Arid|Humid|Cold
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