Final answer:
In the last 250 years, the human population has doubled from 1 billion to 2 billion, and then from 2 billion to 4 billion, meaning it has doubled twice in this time frame. We have not yet reached the third doubling to 8 billion, but we are approaching it as the current population exceeds 7 billion.
Step-by-step explanation:
The human population has experienced several doublings over the last 250 years. Beginning around the time of the Industrial Revolution, the human population stood at approximately 1 billion in 1810. From there, the journey to 2 billion took 120 years, reaching in 1930. The progression continued more rapidly with each subsequent billion added in significantly shorter time frames: 30 years to reach 3 billion by 1960, 15 years for 4 billion by 1975, 14 years for 5 billion by 1989, and just 10 years for 6 billion by 1999. Afterward, it slightly decelerated, taking 12 years to reach 7 billion in 2011.
Following this historical trend, if we estimate the number of doublings, starting from 1 billion in 1810, we see the population first doubled by 1930 to 2 billion. The second doubling to approximately 4 billion would have occurred by around the mid-1970s. Given the current world population is now surpassing 7 billion and heading towards 8 billion, we have not quite reached the third doubling, but we are on the cusp of it.
Exponential growth in human population has continued due to scientific advances and other factors that have improved healthcare and living conditions. However, the growth rate has varied with time, with recent predictions suggesting the rate is slowing. As per recent projections, if the current growth rate of about 1.4% per year continues, a complete third doubling from 4 to 8 billion would be realized a little after the year 2020.