This site has a wealth of information on past and projected population growth, including historical growth rates.
The world bank site has a wealth of data on many topics that intersect economics, environmental and geographic factors.
Finally, the shape of things to come website is a great resource for age distribution data to help students compare outlooks for different countries side by side.
This site is an amazing resource to look at the climate, soil type and vegetation of a particular area. The whole globe is searchable.
This story maps site is about the age of humans and explores many ways we are affecting the environment.
This compound interest calculator is a good tool to predict future human growth. Just substitute current population for principal and enter current growth rate as the interest rate and watch the population increase!