Dec 05 2010
Scribe Post, Human Population.
Friday in class we learned about human population growth rates. We watched a video. Here is a link to that http://www.youtube.com/watch?v=4BbkQiQyaYc
The world population is around 6.9 billion people right now.
Up to 1800- 1 billion
1938- 2 billion
1960-3
1975-4
1987-5
1999-6
This graph shows the growth in population over time for humans. It is an exponential J curve; however, the growth rate has actually decreased from 2.19% in 1960 to 1.2 in 2010. We are still growing exponentially but the drop shows that we may be close to an inflection point. It took us 15 years to get from 3 billion to 4 then 12 years from 4 to 5, but it took us another 12 to get to 6. Now in 2010 we still don’t have 7 billion people and it has been 11 years.
Then we did population calculations using the rule of 70 to show doubling time. AGR stands for Annual Growth Rate and is always a percent. In this problem we are trying to find out the doubling time for an AGR of 1.5%.
70/AGR(%) =Doubling Time
70/(1.5%)=46.6 years≈47 years
2010+47=2057
We won’t have calculators so you must do long division by hand to show your work.
The is equation determine the AGR or rate of annual increase as it is sometimes called. CBR is crude birth rate and CDR is crude death rate. CBR is births + immigration and CDR is deaths + emigration. Crude just means out of 1000, but you multiply by 100 and 2 zeros cancel. This equation is essential in the next equation because AGR helps calculate population growth per year.
(CBR-CDR)/10=AGR%
(14-9)/10=.5%
The final thing we did was Rate of Annual Increase. THis is when you want to find how much a population has grown or will grow if it is a projection. I have attached a picture of one way to do it(3APES at the bottom), but I prefer to take the population say 100 and multiply is by the growth rate say 2%. Then add that to the population.
100*.02=2+100=102
This works-the only error is “CBR is births + immigration and CDR is deaths + emigration.” That is the equation for the change in a population (all factors). When working with CBR or CDR you are just looking at births/deaths. I recommend you delete that sentence from that paragraph and move it up earlier in the discussion. Most of our calculations (esp. for world population) ignore migrations in or out.
Oh, and you never link to original source of image-a must when you borrow images.