Year	Kg per Square Metre
1980	23.77
1981	23.97
1982	24.17
1983	24.36
1984	24.55
1985	24.73
1986	24.91
1987	25.09
1988	25.26
1989	25.45
1990	25.64
1991	25.84
1992	26.03
1993	26.23
1994	26.42
1995	26.63
1996	26.84
1997	27.06
1998	27.26
1999	27.45
2000	27.6
2001	27.73
2002	27.87
2003	28.03
2004	28.18
2005	28.34
2006	28.51
2007	28.69
2008	28.88