| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 33.8 | 53 |
| 2014 | 25.4 | 60 |
| 2013 | 26 | 57 |
| 2012 | 15.8 | 79 |
| 2011 | 12.6 | 87 |
| 2010 | 12.3 | 86 |
| 2009 | 9 | 89 |
| 2008 | 13.3 | 94 |
| 2007 | 6.5 | 112 |
| 2006 | 4.6 | 106 |
| 2005 | 7.6 | 86 |
| 2004 | 4.5 | 87 |
| 2003 | 2.7 | 93 |
| 2002 | 0.5 | 130 |
| 2001 | 0.8 | 116 |
| 2000 | 2.8 | 71 |
| 1999 | 1.8 | 89 |
| 1998 | 1.9 | 96 |
| 1997 | 1.4 | 97 |
| 1996 | 0.1 | 142 |
| 1995 | 0 | 156 |
| 1994 | 0.1 | 130 |
| 1993 | 0.1 | 121 |
| 1992 | 0 | 126 |
| 1991 | 0 | 127 |
| 1990 | 0 | 120 |
| 1989 | 0 | 123 |
| 1988 | 0 | 111 |
| 1987 | 0 | 107 |
| 1986 | 0 | 99 |