| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2015 | 1.7 | 141 |
| 2014 | 3.6 | 129 |
| 2013 | 4.9 | 110 |
| 2012 | 3.3 | 134 |
| 2011 | 1.4 | 143 |
| 2010 | 0.4 | 171 |
| 2009 | 0.6 | 153 |
| 2008 | 0.3 | 174 |
| 2007 | 0.2 | 177 |
| 2006 | 0.8 | 155 |
| 2005 | 0.3 | 154 |
| 2004 | 0 | 172 |
| 2003 | 0.3 | 150 |
| 2002 | 0.2 | 150 |
| 2001 | 0.1 | 151 |
| 2000 | 0.2 | 142 |
| 1999 | 0.1 | 150 |
| 1998 | 0 | 162 |
| 1997 | 0.1 | 159 |
| 1996 | 0.2 | 138 |
| 1995 | 0.1 | 134 |
| 1994 | 0.2 | 117 |
| 1993 | 0 | 144 |
| 1992 | 0 | 128 |
| 1991 | 0 | 134 |
| 1990 | 0 | 129 |
| 1989 | 0.1 | 104 |
| 1988 | 0 | 105 |
| 1987 | 0 | 117 |
| 1986 | 0 | 96 |