Page 707 - Environment: The Science Behind the Stories

Graph Type: Line Graph Yearly data show an increase in ozone
hole size before the Montreal Protocol,
A line graph is used when a data set involves a sequence of and stabilization afterwards
some kind, such as a series of values that occur one by one 30
and change through time or across distance. In a line graph, a
line runs from one data point to the next. Line graphs are most 25 Montreal
Protocol
appropriate when the y-axis expresses a continuous numerical
variable, and the x-axis expresses either continuous numerical 20
data or discrete sequential categories (such as years). FIGURE B.2 Millions of sq km 15
shows values for the size of the ozone hole over Antarctica in
recent years. Note how the data show that the size of the hole 10
increases until 1987, when the Montreal Protocol (p. 490) came 5
into force, and then begins to stabilize afterwards.
0
1979 1985 1990 1995 2000 2005 2010
Year
FIGURE B.2 Size of the Antarctic ozone hole before and after
a treaty that was designed to address it. (Figure 17.27, p. 490)

Plotting these two data sets together reveals
that they rise and fall in tandem and suggests
that they may influence one another

160,000
One useful technique is to plot two or more data
140,000
Numbers of hares and lynx 100,000 Hare Lynx may be related, and if so, the nature of that rela-
sets together on the same graph. This allows us to
120,000
compare trends in the data sets to see whether they
tionship. In FIGURE B.3, recorded numbers of a pred-
80,000
ator species rise and fall immediately following
60,000
those of its prey, suggesting a possible connection.
40,000
20,000

0
1850 1860 1870 1880 1890 1900 1910 1920 1930 1940
Year
FIGURE B.3 Fluctuations in recorded numbers of hare and lynx
in Canada. (Figure 4.4, p. 96)

Key Concept: Projections 8 Developing countries

Besides showing observed data, graphs can show data that are Developed countries Projected future
predicted for the future. Such projections of data are based on 6 data are plotted
models, simulations, or extrapolations from past data, but they as a dashed line
are only as good as the information that goes into them—and Global population (billions) 4
future trends may not hold if conditions change in unforeseen Known past data
are plotted as a
ways. Thus, in this textbook, projected future data are shown solid line
with dashed lines, as in FIGURE B.4, to indicate that they are less 2
certain than data that have already been observed. Be care-
ful when interpreting graphs in the popular media and on the 0
Internet, however; often newspapers, magazines, web sites, 1950 1975 2000 2025 2050
and advertisements will show projected future data in the Year
same way as known past data! FIGURE B.4 Past and projected population growth for
developing and developed countries. (Figure 8.21, p. 225)
B-2

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