| Year | Production (billion tons) | Year | Production (billion tons) |
| 2003 | 1.72 | 2007 | 2.53 |
| 2004 | 1.99 | 2008 | 2.80 |
| 2005 | 2.20 | 2009 | 2.97 |
| 2006 | 2.37 | 2010 | 3.24 |