Year	Kg per Square Metre
1980	21.79
1981	21.84
1982	21.9
1983	21.95
1984	22
1985	22.06
1986	22.11
1987	22.16
1988	22.2
1989	22.25
1990	22.29
1991	22.32
1992	22.33
1993	22.34
1994	22.33
1995	22.29
1996	22.23
1997	22.18
1998	22.13
1999	22.09
2000	22.06
2001	22.04
2002	22.02
2003	22.01
2004	22.01
2005	22.01
2006	22.01
2007	22.01
2008	22.02