Following initial growth rates that averaged 10% to 25% per year in the 1830s through 1850s, it grew at about 4% per year through the last four decades of the 19th century. After a steady slowing of growth in the first four decades of the 20th century to a rate of about 2% per year in the 1930s (the Great Depression years), growth boomed to an average of 6% per year for the decade around 1960, staying around 4% to 5% through 1990. After 1990, average annual growth again slowed steadily to a rate around 2.2% for the ten years ending 2015, approximately double the average world population growth rate of 1.1% for the same period.
Following initial rapid increases averaging 10% to 25% per year in the 1830s through 1850s, it grew at about 4% per year through the last four decades of the 19th century. After a gradual decrease in growth during the first four decades of the 20th century to an average rate of about 2% per year in the 1930s (the Great Depression years), growth surged to an average of 6% per year for the decade around 1960, remaining at 4% to 5% through 1990. After 1990, annual growth again slowed steadily to a rate around 2.2% for the ten years ending 2015, roughly double the average global population growth rate of 1.1% for the same period.