Year	Kg per Square Metre
1980	25.17
1981	25.19
1982	25.2
1983	25.22
1984	25.22
1985	25.21
1986	25.21
1987	25.19
1988	25.17
1989	25.15
1990	25.14
1991	25.05
1992	24.97
1993	24.94
1994	24.94
1995	24.94
1996	24.97
1997	24.97
1998	25
1999	25.06
2000	25.13
2001	25.2
2002	25.27
2003	25.33
2004	25.4
2005	25.47
2006	25.53
2007	25.59
2008	25.66