| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 3.2 | 127 |
| 2014 | 4.6 | 119 |
| 2013 | 0.7 | 156 |
| 2012 | 7.5 | 108 |
| 2011 | 4.5 | 125 |
| 2010 | 3.4 | 121 |
| 2009 | 0.5 | 157 |
| 2008 | 2.6 | 135 |
| 2007 | 1.1 | 157 |
| 2006 | 1.9 | 132 |
| 2005 | 0.1 | 170 |
| 2004 | 0.9 | 127 |
| 2003 | -.6 | 185 |
| 2002 | 0.9 | 115 |
| 2001 | 1 | 108 |
| 2000 | 1.1 | 109 |
| 1999 | 0.9 | 107 |
| 1998 | 3.4 | 75 |
| 1997 | 2.4 | 81 |
| 1996 | 1.5 | 81 |
| 1995 | 1 | 85 |
| 1994 | 1.4 | 69 |
| 1993 | 0.8 | 83 |
| 1992 | 1.2 | 60 |
| 1991 | 0.9 | 62 |
| 1990 | 0.8 | 61 |
| 1989 | 0.1 | 87 |
| 1988 | 0.1 | 96 |
| 1987 | 0.1 | 99 |
| 1986 | 0 | 108 |