Below is a chart calculating world population using the low variant scale, which is the historically accurate one. This scale seems accurate up to present date so I can assume it's validity, but look at the year 2100.  The world population drops below present values. How intriguing.




Source: Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat,  
World Population Prospects: The 2010 Revision




For definition of variables, check the link 
Sunday, April 29, 2012; 11:45:35 AM

World
Population (thousands)
Low variant
1950-2100

Year   Population

1950   2 532 229
1955   2 772 882

1960   3 038 413

1965   3 333 007

1970   3 696 186

1975   4 076 419

1980   4 453 007

1985   4 863 290

1990   5 306 425

1995   5 726 239

2000   6 122 770

2005   6 506 649

2010   6 895 889

2015   7 217 275

2020   7 480 225

2025   7 689 135

2030   7 867 332

2035   8 006 642

2040   8 096 725

2045   8 131 432

2050   8 112 191

2055   8 046 170

2060   7 940 112

2065   7 798 443

2070   7 624 235


2075   7 420 399

2080   7 191 850

2085   6 946 100

2090   6 691 274

2095   6 433 361

2100   6 177 378