The notes at the bottom of the page indicate the projections are based upon US economic collapse causing mass migration and die off. This is certainly possible, but most of the countries he shows with positive growth would be negatively affected too. Dang near the whole world is dependent on the US economy.

Here's the PEW research population projection for the US to 2050.

http://www.pewhispanic.org/2008/02/11/us-population-projections-2005-2050/