Stories
Slash Boxes
Comments

SoylentNews is people

posted by martyb on Wednesday May 06 2020, @02:53AM   Printer-friendly
from the waste-not-want-not dept.

Arthur T Knackerbracket has found the following story:

The area of agricultural land that will require irrigation in future could be up to four times larger than currently estimated, a new study has revealed.

Research by the University of Reading, University of Bergen and Princeton University shows the amount of land that will require human intervention to water crops by 2050 has been severely underestimated due to computer models not taking into account many uncertainties, such as population changes and availability of water.

The authors of the study, published in Geophysical Research Letters, argue forecasters and policy-makers need to acknowledge multiple future scenarios in order to be prepared for potential water shortages that would have huge environmental costs.

[...] "If the amount of water needed to grow our food is much larger than calculated, this could put severe pressure on water supplies for agriculture as well as homes. These findings show we need strategies to suit a range of possible scenarios and have plans in place to cope with unexpected water shortages."

[...] The new research suggests that projections of irrigated areas made by the Food and Agriculture Organization of the United Nation and others have always underestimated the amount of irrigation required in future by basing them on other assumptions.

The study highlights that the potential global extension of irrigation might be twice, or in the most extreme scenario, even four times larger than what has been suggested by previous models.

[...] Agricultural land where crops cannot be supported by rainwater alone is often irrigated by channelling water from rivers or springs, sprinkler systems, or by controlled flooding. Increased irrigation in future would mean more water consumption, machinery, energy consumption and fertilisers, and therefore more greenhouse gas emissions.

Journal Reference
A. Puy, S. Lo Piano, A. Saltelli. Current Models Underestimate Future Irrigated Areas, Geophysical Research Letters (DOI: 10.1029/2020GL087360)


Original Submission

 
This discussion has been archived. No new comments can be posted.
Display Options Threshold/Breakthrough Mark All as Read Mark All as Unread
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
  • (Score: 1) by khallow on Wednesday May 06 2020, @04:44AM (9 children)

    by khallow (3766) Subscriber Badge on Wednesday May 06 2020, @04:44AM (#990975) Journal
    My point is that the alleged superexponential function grows slower than an exponential function upper bound! And if we tried to put a γ>1, we'd hit a singularity infinity in short order - faster than double exponentials BTW!
  • (Score: 2, Informative) by Anonymous Coward on Wednesday May 06 2020, @05:35AM (8 children)

    by Anonymous Coward on Wednesday May 06 2020, @05:35AM (#990983)

    I still don't get your point then. Double exponential functions grow faster than exponential functions or even factorial functions. You can trivially construct an exponential function that will grow faster in the short term to a given double exponential function, but the growth curve of the double exponential function will win eventually (same as can be done with a linear function for a given exponential function). Nor does that doesn't change the fact that the human growth curve has been super-exponential in nature for quite some time until near-modernity.

    • (Score: 1) by khallow on Wednesday May 06 2020, @12:09PM (7 children)

      by khallow (3766) Subscriber Badge on Wednesday May 06 2020, @12:09PM (#991030) Journal

      Nor does that doesn't change the fact that the human growth curve has been super-exponential in nature for quite some time until near-modernity.

      Assertions don't make it so. It's physically impossible to have superexponential growth in the first place. Even if women bore as many children as possible, it'd probably cap out around one doubling of population every decade or so.

      You can trivially construct an exponential function that will grow faster in the short term

      The point is that you can't construct a superexponential function that successfully models global human population growth over long periods of time because it is bounded from above by an exponential function. Further, they model population growth rate as a power of the present population. Any superexponential growth of that particular model (which corresponds to an exponent greater than one) naturally has an infinite singularity in finite time. In other words, it predicts an impossible result in finite time - so their model doesn't make sense in a regime that they claim existed for much of human history.

      • (Score: 2) by HiThere on Wednesday May 06 2020, @03:13PM (6 children)

        by HiThere (866) Subscriber Badge on Wednesday May 06 2020, @03:13PM (#991064) Journal

        The maximal growth rate for humans is faster than you are supposing, but it *is* bounded by an exponential function. I suspect that the maximal growth rate would be one child per woman per 18 months between the ages of, say, 15 and 45. And all children surviving. That's not very realistic, but it is an reasonable upper bound.

        --
        Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
        • (Score: 1) by khallow on Wednesday May 06 2020, @03:26PM (3 children)

          by khallow (3766) Subscriber Badge on Wednesday May 06 2020, @03:26PM (#991069) Journal

          between the ages of, say, 15

          That time lag is a large part of the reason I asserted doubling was on the order of 10 years. Having children sooner is more important for fast population growth than having more children over a long time span. Ok, I'll download Libre Office to calculate the true exponential rate. Then you will all pay!

          • (Score: 1) by khallow on Wednesday May 06 2020, @03:47PM (2 children)

            by khallow (3766) Subscriber Badge on Wednesday May 06 2020, @03:47PM (#991073) Journal
            Ok, for women who have kids every year from 15 to 45, I get a population double time of.... 5.08 years. Much higher than I was expecting. Every 18 months will be somewhat longer doubling time, but not 5 years longer methinks.
            • (Score: 1) by khallow on Wednesday May 06 2020, @03:56PM

              by khallow (3766) Subscriber Badge on Wednesday May 06 2020, @03:56PM (#991079) Journal
              Sigh, the online poly root solvers I'm using choke on degree 90 polynomials. Wimps.

              Here's the polynomial I'm presently trying to factor:

              x^90-x^60-x^57-x^54-x^51-x^48-x^45-x^42-x^39-x^36-x^33-x^30-x^27-x^24-x^21-x^18-x^15-x^12-x^9-x^6-x^3-1=0

              Multiplication by x is a time step of half a year. This corresponds to saying the number of births 45 years in the future is equal to the number of women who were born in the years 0 through 30 in the future, every 3/2 of a year (which is 18 months). Anyway, once I factor the polynomial, I look for the largest root and that's my exponential factor.

              I also noticed that this works only if I assume women only give birth to more women.
            • (Score: 1) by khallow on Wednesday May 06 2020, @04:00PM

              by khallow (3766) Subscriber Badge on Wednesday May 06 2020, @04:00PM (#991082) Journal
              Assuming equal numbers of women and men brings the doubling time to 6.61 years. 10 years doubling time might be about right for your version of the problem. The polynomial to factor is:

              2x^90-x^60-x^57-x^54-x^51-x^48-x^45-x^42-x^39-x^36-x^33-x^30-x^27-x^24-x^21-x^18-x^15-x^12-x^9-x^6-x^3-1=0
        • (Score: 0) by Anonymous Coward on Wednesday May 06 2020, @07:52PM (1 child)

          by Anonymous Coward on Wednesday May 06 2020, @07:52PM (#991139)

          You are both forgetting many important in human populations. First is that humans don't have distinct generations relative to their lifetime. They overlap to the point where a person can be alive and have grandchildren older than their children. Second is that humans have lived longer over time. Each month of life expectancy adds to the total population of that month due to generational overlap and to the mean number of children per generation by extending reproductive age. Third is that child mortality rate is dropping, meaning that more humans as a proportion of their generation are reaching reproductive age.

          Those are just the big three factors and their most obvious ways of affecting human population. There are tons of papers, including the two that TFA cites, on this subject and plenty of free resources online at a simple web or literature search. Feel free to look it up yourself. Many go into great detail as to why an exponential function won't work for human population data.

          • (Score: 1) by khallow on Wednesday May 06 2020, @10:04PM

            by khallow (3766) Subscriber Badge on Wednesday May 06 2020, @10:04PM (#991176) Journal

            You are both forgetting many important in human populations. First is that humans don't have distinct generations relative to their lifetime.

            Second is that humans have lived longer over time. Each month of life expectancy adds to the total population of that month due to generational overlap and to the mean number of children per generation by extending reproductive age.

            Third is that child mortality rate is dropping, meaning that more humans as a proportion of their generation are reaching reproductive age.

            None of these items are relevant to the population growth extremes we were discussing.