Statistics you must find from the library, your text, the ...



Worksheet for Estimating Potential Limits to Population Growth - Science 1102 - Dr. D.

There is no single "right" answer to each of these questions. I expect answers to vary from student to student. As you make these estimates, you will have to make decisions on what numbers to use and how to calculate your estimates. That is part of the point of this exercise. Fill in the empty boxes :

|Column A |Column B |Column C |

|Statistics you must find from the library, your text, the |Calculation you used to estimate value in |Your estimate. Do not use previously published estimates|

|internet, lecture, etc. |Column C (show equation or describe). Some equations or hints are given. |in this column, rather derive your estimates based on |

| | |stats from Column A. |

Section 1: Estimating Future Population Size

|Column A Statistic to look up |Column B Calculation |Column C Your estimate |

|A1. Global population size in the year (Y1) |B1. Calculation for annual growth rate: |C1. Annual growth rate (“percent growth”) based on your |

|(any year prior to Y2 below): | |A1 and A2 estimates: |

| |C1 = [(A2-A1)/A1] * 100 | |

| |(Y2-Y1) | |

|A2. Global population size at present (or recent) year | | |

|(Y2) ________ (later than Y1): |show work: | |

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|A3. None: you will use figure derived in C1 |B3. Calculation for doubling time: |C3. Doubling time (years): |

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| |Hint: use equation on p. 78 | |

Section 2: Estimating Available Agricultural Land

|Column A Statistics |Column B Calculation |Column C Your estimate |

|A4. Amount of Earth's land that can be potentially used |Briefly explain how you derived your estimates of A4 and A5 and cite your source: |C4. Ratio of all potential agricultural land to land |

|for agriculture (potential arable or cultivable land): | |currently used by agriculture: |

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|A5. Amount of Earth's land that is currently being used | | |

|for agriculture: | | |

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|Hint: see ‘Helpful References’ section |B4. Calculation for Ratio in C4: | |

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|A6. None: you will use figures derived above |B6. Calculation for C6: |C6. Potential number of people the Earth can support |

| | |based on the agricultural land available (C4): |

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| |Hint: Use A2 and C4 to calculate C6 (see ‘Math Reminders’ section) or just estimate | |

|A7. None: you will use figures derived above |B7. Use your estimate from C6 and the graph of “projected population size” in the |C7. Number of years until Earth's population is so large |

| |back section of this handout. |that all potential agricultural is being used: |

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Section 3: Estimating Available Freshwater

|Column A Statistics |Column B Calculation |Column C Your estimate |

|A8. Percent of ‘runoff’ used by humans (Estimate from |Briefly explain how you derived your estimates of A8 and cite your source: |C8. Ratio of Earth's available runoff to runoff used by |

|information in Chapter 10 of the textbook, OR find from | |humans: |

|the attached article “Anthropogenic Disturbance of the | | |

|Terrestrial Water Cycle.”): | | |

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| |B8. Calculation for Ratio in C8: | |

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| |Hint: a ‘percentage’ is the ratio a number to 100. | |

|A9. None: you will use figures derived above |B9. Calculation for C9 |C9. Potential number of people the Earth can support |

| | |based on all available runoff (C8): |

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| |Hint: Use A2 and C8 to calculate C9 (see ‘Math Reminders’ section) or just estimate | |

|A10. None: you will use figures derived above |B10. Use your estimate from C9 and the graph of “projected population size” in the |C10. Number of years until Earth's population is so large|

| |back section of this handout. |that all availble runoff water is being used: |

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BEFORE YOU TURN THIS WORKSHEET IN, GO TO THE CLASS WEB PAGE AND ENTER YOUR DATA IN THE "Population Worksheet Survey Form"

Questions to be answered and turned in with this worksheet:

1. Assuming that all your raw data and calculations are correct, what else does your estimate of “doubling time” (C3) assume (i.e. what conditions might cause this estimate to become wrong)?

2. Assuming that all your raw data and calculations are correct, what else does your estimate of “population size the earth can support” (C6 or C9) assume (i.e. what conditions might cause this estimate to become wrong)?

3. Do you think that your estimate of the “total number of people the Earth could support” would change if everyone on Earth lived at the average U.S. standard of living? Explain your answer and make a guess on this number.

Projected Population Size graph:

[pic]

Source: United Nations

Helpful mathematical reminders:

• To estimate one variable from another using a line graph, find the known variable value on the appropriate axis and sketch a line perpendicular to that axis from that point. Where your sketched line intersects the line on the graph, sketch another line perpendicular to the first sketched line. Where this second line intersects the other axis is the value of your unknown variable.

• A ratio is simply a comparison of two numbers in which one number is divided by a second. So the ratio of 100 to 50 can be expressed as 100:50 or 100/50 or 2:1 or 2/1 or "the first number is 2 times as large as the second".

• If you are assuming the ratio of A to B is the same as the ratio of C to D, then the if you know A, B, and D and wish to calculate C, then C=(A/B)*D. So, for example, if the ratio of all potential agricultural land to land currently used by agriculture is 4:3 and the global population size at present is 6.3 billion, then:

|Number of people the Earth can support based on the | |

|agricultural land used presently |= (4/3) * 6,000,000,000 |

Helpful references for finding the required stats:

I have found a few web sites helpful in estimating the amount of agricultural land:

1.

The difficulty with this site is that there are not statistics available for the entire world, so you will have to sum the arable lands (both for potential and for actual,, separately) for each of the seven world regions. To use, select the ‘Actual and potential available arable land’ near the bottom of the Terrastat database list, and then the world region, and hit the display statistic button. The stats will be listed by country, but don’t panic, they are summed by region at the bottom of the table.

2.

This website is an essay that provides separate estimates for developing and developed countries for “cultivable” and “under cultivation” so you will have to use a little math to calculate C4 (the ratio of all potential agricultural land to land currently used by agriculture).

3.

The difficulty with this site is that the terminology is confusing. The term ‘Agricultural Area’ appears to be all land that is farmed (permanent and actual arable) and permanent pasture. The term “Arable and Permanent Crops” appears to estimate all land actually being farmed but not grazed. This site does not appear to estimate potential arable land. To use, select "Land use" in table to go to stat calculator form. Be sure to select an option in all four of the menu boxes before submitting the form. Use “WORLD+” under country menu.

Other sites on agriculture of interest:

ifpri.2020/synth/islam.htm









For the statistic in A8, the following exert from an article in the journal “Bioscience” may be useful.

[pic]



Anthropogenic Disturbance of the Terrestrial Water Cycle.

Author/s: Charles J. Vorosmarty

Issue: Sept, 2000

RECENT ANALYSIS DEMONSTRATES THAT HYDRAULIC ENGINEERING HAS PRODUCED GLOBAL-SCALE IMPACTS ON THE TERRESTRIAL WATER CYCLE

The terrestrial water cycle plays a central role in the climate, ecology; and biogeochemistry of the planet. Mounting historical evidence for the influence of greenhouse warming on recent climate, and modeling projections into the future, highlight changes to the land based water cycle as a major global change issue (Houghton et al. 1995, Watson et al. 1996, SGCR 1999). Disturbance of the hydrologic cycle has received significant attention with respect to land--atmosphere exchanges, plant physiology, net primary production, and the cycling of major nutrients (Foley et al. 1996, Sellers et al. 1996, McGuire et al. 1997). Changes in land use are also recognized as critical factors governing the future availability of fresh water (Chase et al. 2000).

Another important but seldom articulated global change issue is direct alteration of the continental water cycle for irrigation, hydroelectricity, and other human needs. Although the scope and magnitude of water engineering today are colossal in comparison with preindustrial times, most of the very same activities--irrigation, navigation enhancement, reservoir creation--can be traced back several thousand years in the Middle East and China. Stabilization of water supply has remained a fundamental preoccupation of human society and is a key security concern for most nations. Reducing flood hazard, enhancing food security, and redirecting runoff from water-rich to water-poor areas continue to provide a major challenge to our engineering infrastructure.

In this article we address three issues. First, we document the nature and magnitude of direct human alteration of the terrestrial water cycle, specifically through construction of engineering works for water resource management. We focus on the redistribution of freshwater among major storage pools and the corresponding changes to continental runoff. Second, we explore some of the impacts of this disturbance on drainage basins, river systems, and land-to-ocean linkages. Finally, we review key uncertainties regarding our current understanding of human-water interactions at the global scale and make suggestions on potentially useful avenues for future research.

Evidence for global-scale human impacts on the terrestrial water cycle

Although an exact inventory of global water withdrawal has been difficult to assemble, the general features of anthropogenic water use are more or less known. Reviews of the recent literature (Shiklomanov 1996, Gleick 2000) show a range in estimated global water withdrawals for the year 2000 between approximately 4000 and 5000 km3/yr Despite reductions in the annual rate of increase in withdrawals from 1970 (Shiklomanov 1996, 2000, Gleick 1998a), global water use has grown more or less exponentially with human population and economic development over the industrial era. By one account (L'vovich and White 1990), there was a 15-fold increase in aggregate water use between 1800 and 1980, when the global population increased by a factor of four (Haub 1994). Aggregate irretrievable water losses (consumption), driven mainly by evaporation from irrigated land, increased 13-fold during this period. Global consumption for 1995 has been estimated at approximately 2300 km3/yr, or 60% of total water withdrawal (Shiklomanov 1996). To place such water use into perspective, it is necessary to consider the global supply of renewable water. Using recent estimates of long-term average runoff from the continents totaling approximately 40,000 km3/yr (Fekete et al. 1999, Shiklomanov 2000) and an estimated withdrawal of 4000-5000 km3/yr, humans exploit from 10% to 15% of current water supply. It therefore might appear that water withdrawal over the entire globe is but a small fraction of continental runoff and that water poses no major limitation to human development. However, of the 31% of global runoff that is spatially and temporally accessible to society, more than half is withdrawn (35%) or maintained for instream uses (19%; Postel et al. 1996). And, by the early 1990s, several arid zone countries showed relative use rates much larger than the global average (e.g., Azerbaijan, Egypt, and Libya, which were already using 55%, 110%, and 770% of their respective sustainable water supplies; WRI 1998). Contemporary society is thus highly dependent on, and in many places limited by, the terrestrial water cycle defined by contemporary climate.

This dependency is likely to intensify as a consequence of population growth and economic development. From 1950 to 1998, water availability had already decreased from 16,000 to 6700 m3/yr per capita (WRI 1998, Fekete et al. 1999). If we assume no appreciable change in global runoff over the next several decades, a projected increase in global population by 2025 to approximately 8 billion people (WRI 1998) means that per capita supplies will continue to decline to approximately 5000 m3/yr (WRI 1998). Tabulating these statistics from the standpoint of accessible water, per capita availability would be reduced to approximately 1500 m3/yr. Given an estimate of mean global water use of 625 m3/yr per capita for 2025 (Shiklomanov 1996, 1997), withdrawals could therefore exceed 40% of the accessible global water resource even with presumed increases in use efficiency. This has obvious implications for human society and natural ecosystems, both of which are highly dependent on renewable s upplies of water.

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