What is the key concept for this section? What is the range of estimates for the size of the human population in 2050? Summarize the three major population growth trends recognized by demographers....

What is the key concept for this section? What is the range of estimates for the size of the human population in 2050? Summarize the three major population growth trends recognized by demographers. About how many people were added to the world’s population in 2015? What are the world’s three most populous countries? List eight major ways in which we have altered natural systems to meet our needs. Define cultural carrying capacity. Summarize the debate over whether and how long the human population can keep growing.