| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 4 | 121 |
| 2014 | 4.7 | 118 |
| 2013 | 3.7 | 122 |
| 2012 | 3.5 | 131 |
| 2011 | 3.4 | 132 |
| 2010 | 1.2 | 148 |
| 2009 | 1.1 | 146 |
| 2008 | 0.5 | 165 |
| 2007 | 0.7 | 168 |
| 2006 | 0.4 | 164 |
| 2005 | 1 | 134 |
| 2004 | 0.1 | 166 |
| 2003 | 0 | 173 |
| 2002 | 0.3 | 143 |
| 2001 | 0 | 161 |
| 2000 | 0.2 | 143 |
| 1999 | 0.6 | 117 |
| 1998 | 4.4 | 68 |
| 1997 | 1.4 | 98 |
| 1996 | 0.8 | 103 |
| 1995 | 1.2 | 80 |
| 1994 | 0.3 | 103 |
| 1993 | 0.3 | 103 |
| 1992 | 0.1 | 103 |
| 1991 | 0 | 120 |
| 1990 | -.1 | 140 |
| 1989 | -.1 | 137 |
| 1988 | -.2 | 138 |
| 1987 | -.3 | 137 |
| 1986 | 0.1 | 82 |