Year	Kg per Square Metre
1980	26.19
1981	26.2
1982	26.2
1983	26.19
1984	26.19
1985	26.18
1986	26.17
1987	26.15
1988	26.12
1989	26.09
1990	26.05
1991	26
1992	25.92
1993	25.79
1994	25.67
1995	25.59
1996	25.55
1997	25.54
1998	25.52
1999	25.48
2000	25.45
2001	25.43
2002	25.43
2003	25.44
2004	25.47
2005	25.5
2006	25.55
2007	25.6
2008	25.67