Year	Kg per Square Metre
1980	24.11
1981	24.13
1982	24.15
1983	24.17
1984	24.19
1985	24.19
1986	24.2
1987	24.22
1988	24.23
1989	24.25
1990	24.26
1991	24.25
1992	24.23
1993	24.19
1994	24.13
1995	24.07
1996	24.01
1997	23.96
1998	23.92
1999	23.92
2000	23.94
2001	23.98
2002	24.05
2003	24.14
2004	24.24
2005	24.36
2006	24.47
2007	24.57
2008	24.66