Year	Kg per Square Metre
1980	26.26
1981	26.24
1982	26.22
1983	26.2
1984	26.17
1985	26.15
1986	26.14
1987	26.12
1988	26.11
1989	26.1
1990	26.09
1991	26.08
1992	26.06
1993	26.04
1994	25.99
1995	25.96
1996	25.93
1997	25.95
1998	25.97
1999	25.98
2000	26.02
2001	26.07
2002	26.12
2003	26.18
2004	26.25
2005	26.33
2006	26.44
2007	26.54
2008	26.64