| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 21.7 | 66 |
| 2014 | 21.3 | 65 |
| 2013 | 9.5 | 89 |
| 2012 | 2.8 | 139 |
| 2011 | 6.3 | 118 |
| 2010 | 2.9 | 125 |
| 2009 | 2.2 | 123 |
| 2008 | 1.1 | 154 |
| 2007 | 2.2 | 135 |
| 2006 | 5.5 | 99 |
| 2005 | 2.7 | 112 |
| 2004 | 5.5 | 84 |
| 2003 | 4.7 | 80 |
| 2002 | 2.6 | 86 |
| 2001 | 3.5 | 77 |
| 2000 | 1.3 | 98 |
| 1999 | 0.7 | 113 |
| 1998 | 2.6 | 82 |
| 1997 | 2.9 | 76 |
| 1996 | 0.2 | 126 |
| 1995 | 0.1 | 128 |
| 1994 | 0.2 | 120 |
| 1993 | 0 | 142 |
| 1992 | 0 | 145 |