Year	Kg per Square Metre
1980	18.64
1981	18.71
1982	18.79
1983	18.86
1984	18.93
1985	19
1986	19.08
1987	19.16
1988	19.24
1989	19.32
1990	19.39
1991	19.47
1992	19.56
1993	19.66
1994	19.77
1995	19.88
1996	20
1997	20.12
1998	20.23
1999	20.34
2000	20.43
2001	20.52
2002	20.61
2003	20.68
2004	20.76
2005	20.83
2006	20.91
2007	21
2008	21.08