Year	Kg per Square Metre
1980	25.91
1981	26
1982	26.09
1983	26.16
1984	26.23
1985	26.3
1986	26.37
1987	26.44
1988	26.52
1989	26.6
1990	26.7
1991	26.78
1992	26.86
1993	26.92
1994	26.99
1995	27.05
1996	27.13
1997	27.21
1998	27.29
1999	27.39
2000	27.5
2001	27.61
2002	27.74
2003	27.87
2004	27.99
2005	28.1
2006	28.22
2007	28.34
2008	28.45