15. What happened to global airtransportation from 1950 to 1998?

From 1950 to 1998, more and more people use airplane to travel around the world which can decrease the time spending on a certain journey, and the figures in the below table give a detailed description.

Year	People	Freight	Year	People	Freight	Year	People	Freight
1950	28	0.7	1975	697	19.4	1987	1,589	48.3
1955	61	1.2	1976	764	21.5	1988	1,705	53.3
1960	109	2.0	1977	818	23.6	1989	1,774	57.1
1966	229	5.7	1978	936	25.9	1990	1,894	58.8
1967	273	6.5	1979	1,060	28.0	1991	1,845	58.6
1968	309	8.2	1980	1,089	29.4	1992	1,929	62.6
1969	351	9.8	1981	1,119	30.9	1993	1,949	68.4
1970	460	12.0	1982	1,142	31.5	1994	2,100	77.2
1971	494	13.2	1983	1,190	35.1	1995	2,248	83.1
1972	560	15.0	1984	1,278	39.7	1996	2,426	89.2
1973	618	17.5	1985	1,367	39.8	1997	2,570	99.8
1974	656	19.0	1986	1,452	43.2	1998	2,621	99.0

People = Billion passenger kilometers . . . Freight = Billion ton kilometers

Source: Vital Signs 1999, Worldwatch Institute