| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 5.2 | 113 |
| 2014 | 3.5 | 131 |
| 2013 | 5.7 | 106 |
| 2012 | 8.1 | 106 |
| 2011 | 7.4 | 109 |
| 2010 | 8.1 | 95 |
| 2009 | 12.9 | 80 |
| 2008 | 11.3 | 98 |
| 2007 | 7.9 | 103 |
| 2006 | 2.9 | 116 |
| 2005 | 0.9 | 138 |
| 2004 | 0.5 | 149 |
| 2003 | 0.1 | 163 |
| 2002 | 0.1 | 152 |
| 2001 | 0.9 | 111 |
| 2000 | 0.8 | 115 |
| 1999 | 0.6 | 119 |
| 1998 | 0.2 | 146 |
| 1997 | 0.1 | 152 |
| 1996 | 0.1 | 147 |
| 1995 | 0.1 | 136 |
| 1994 | 0.1 | 137 |
| 1993 | 0.2 | 116 |
| 1992 | 0.2 | 94 |
| 1991 | 0.1 | 99 |
| 1990 | 0.2 | 89 |
| 1989 | 0.1 | 86 |
| 1988 | 0 | 106 |
| 1987 | 0 | 106 |
| 1986 | 0.1 | 74 |