# Growth and Decay, Population Change

Growth and decay refer to the direction in which a quantity is changing. If something is growing, it means that a value is increasing (example–world population growth over time). If something is decaying, it means that a value is decreasing (example–population of Japan is decaying over time). A growth or decay factor describes the rate at which a quantity is changing over a certain period of time via a multiplication sequence (factor implies multiplication). For example, to describe a population increase by 10%, multiply by the growth factor 1.10. To describe a population decrease by 10%, multiply by 0.90 (shows a 10% decrease because only 90% of the theoretical population is remaining. A total change is the amount by which a quantity increases or decreases–for example, the total population change for Japan from 2010 to 2016 was a population decrease by 1.13 million (128.06 million in 2010 –> 126.93 million in 2016). The percent change for this population from 2010-2016 would be a 0.88% decrease in population. The average rate of change would be decreasing by .18 million people per year (this means the population is decreasing by less than a quarter of a million people per year). The terms linear growth would refer to a steady decrease per year, resulting in a linear graph while exponential growth or decay means that a quantity is increasing more and more rapidly or decreasing more and more rapidly over time.

See the data for Japan population decay here.

# Population Growth and Sustainability

For my data selection, I chose to examine world population graphs. Below, we see the graph of the changing population from 1750 to the projected population in year 2100. The red line that we see in this graph shows the annual growth rate of the world population. This line expresses how growth was relatively between .4%-.6% from 1750 up through 1930, but after the baby boom post WWII, population growth shot up exponentially. Now, with less people having babies and the population is unable to replenish itself, population growth is now slowing at an exponential rate as well. There are several reasons for this–more women are joining the work force and are either waiting to have kids, having less kids, or not having kids at all. Some women choose not to have children at all due to their perception of the world in its current state, which is something I learned from my political science class this past spring. The other curve seen on this graph is the blue curve of the world population. The dark blue shaded in section represents the actual population growth from 1750 up to 2015. The lighter blue shaded in region represents the projected population growth from 2015 up to the year 2100. The population is still increasing, but at a much slower rate than in the past, which is why the slope of the projected population growth is much less steep than the slope of population growth from 1945 to 2015. This relates to sustainability because our current population growth is not sustainable for our Earth. This is partially due to the amount of food we need to grow to feed this giant population, and the amount of land that we need but do not have to efficiently grow food on (not all land is good for growing crops). This also relates to my research from last week discussing the problems with eating meat, as this population size is not sustainable for having humans be able to consume meat (which the practice of raising the meat in itself isn’t sustainable as well).