Year	Kg per Square Metre
1980	24.19
1981	24.21
1982	24.23
1983	24.25
1984	24.28
1985	24.29
1986	24.31
1987	24.32
1988	24.33
1989	24.32
1990	24.3
1991	24.26
1992	24.18
1993	24.09
1994	23.96
1995	23.84
1996	23.71
1997	23.59
1998	23.48
1999	23.4
2000	23.34
2001	23.32
2002	23.33
2003	23.37
2004	23.43
2005	23.51
2006	23.59
2007	23.68
2008	23.78