Year	Kg per Square Metre
1980	27.18
1981	27.22
1982	27.23
1983	27.22
1984	27.22
1985	27.21
1986	27.2
1987	27.21
1988	27.22
1989	27.25
1990	27.27
1991	27.32
1992	27.37
1993	27.44
1994	27.51
1995	27.58
1996	27.65
1997	27.75
1998	27.86
1999	27.97
2000	28.08
2001	28.19
2002	28.3
2003	28.41
2004	28.52
2005	28.62
2006	28.72
2007	28.82
2008	28.91