Year	Kg per Square Metre
1980	26.83
1981	27.09
1982	27.35
1983	27.58
1984	27.82
1985	28.08
1986	28.31
1987	28.57
1988	28.83
1989	29.08
1990	29.31
1991	29.54
1992	29.76
1993	29.98
1994	30.16
1995	30.37
1996	30.6
1997	30.83
1998	31.07
1999	31.32
2000	31.58
2001	31.85
2002	32.11
2003	32.4
2004	32.67
2005	32.95
2006	33.2
2007	33.44
2008	33.66