Year	Million km2
1979	1.1
1980	3.3
1981	3.1
1982	10.8
1983	12.2
1984	14.7
1985	18.8
1986	14.4
1987	22.4
1988	13.8
1989	21.7
1990	21.1
1991	22.6
1992	24.9
1993	25.8
1994	25.2
1996	26.9
1997	25.1
1998	27.9
1999	25.8
2000	29.9
2001	26.5
2002	21.9
2003	28.4
2004	22.8
2005	27.3
2006	29.6
2007	25.2
2008	27.0
2009	24.4
2010	22.6
2011	26.1
2012	21.1
2013	24.0
2014	24.1
2015	28.2
2016	23.0
2017	19.6
2018	24.8