Final answer:
Using the rule of 70 with a growth rate of 2% per year from a starting population of 5.7 billion in 1995, the world population is estimated to double by the year 2030. Growth rates can change over time, influencing the actual doubling time.
Step-by-step explanation:
The question asks by what year the world population will have doubled given an observed relative growth rate of 2% per year, starting from a population of 5.7 billion in 1995. To calculate this, we use the rule of 70, which is a way to estimate the number of years required to double the population at a constant annual growth rate. According to this rule, you divide 70 by the annual growth rate to find the doubling time in years. In this case, with a 2% growth rate, the doubling time is 70 ÷ 2 = 35 years.
Adding 35 years to the starting year of 1995, the population is estimated to have doubled by the year 2030.
It is important to note that the actual population growth may differ due to a variety of factors affecting birth rates, death rates, and public policy. Additionally, in reality, growth rates can change over time. For instance, between 1965 and 1980, the world population growth rate was around 2%, while recent trends predict a slowdown to close to a 1.1% growth rate during the 2005-2015 period and about 1.4% per year thereafter, which could notably increase the doubling time.