|
| year | production | consumption |
| 1980 | 1.45 | .71 |
| 1981 | 1.48 | .83 |
| 1982 | 1.69 | .93 |
| 1983 | 1.84 | 1.05 |
| 1984 | 2.08 | 1.15 |
| 1985 | 2.23 | 1.21 |
| 1986 | 2.09 | 1.24 |
| 1987 | 2.30 | 1.30 |
| 1988 | 2.24 | 1.30 |
| 1989 | 2.32 | 1.35 |
| 1990 | 2.36 | 1.44 |
| 1991 | 2.40 | 1.43 |
| 1992 | 2.39 | 1.43 |
| 1993 | 2.48 | 1.37 |
| 1994 | 2.52 | 1.56 |
| 1995 | 2.60 | 1.59 |
| 1996 | 2.65 | 1.73 |
| 1997 | 2.51 | 1.79 |
| 1998 | 2.48 | 1.85 |
| 1999 | 2.59 | 1.92 |
| 2000 | 2.55 | 2.01 |
| 2001 | 2.69 | 2.23 |
| 2002 | 2.67 | 2.26 |
| 2003 | 2.85 | 2.43 |
| 2004 | 2.86 | 2.58 |
| 2005 | 3.13 | 2.69 |
| 2006 | 3.19 | 2.54 |
| 2007 | 3.25 | 2.71 |
| 2008 | 3.76 | 3.19 |
| 2009 | 3.92 | 3.20 |
| 2010 | 3.85 | 3.31 |
|
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