241
Mauna Loa in Hawaii is an ideal site
for an atmospheric research station. The
high altitude and remote location of the
volcano ensure that the air is largely
unaffected by humans or vegetation.See also: Global warming 202–203 ■ The biosphere 204–205 ■ Environmental
feedback loops 224–225 ■ Halting climate change 316–321THE HUMAN FACTOR
was sure that he had a long-enough
series of records to detect a year-
on-year increase.Seasonal changes
Although South Pole funding ended
in 1964, Mauna Loa has produced
data from 1958 onward. Plotted on a
graph, the measurements became
known as the Keeling Curve. It is,
in fact, a series of annual curves,reflecting seasonal changes. During
spring and summer in the Northern
Hemisphere, as new foliage takes
more CO 2 out of the atmosphere,
the global concentration of the gas
declines, reaching a low point in
September. It increases again in
the northern autumn as leaves fall
and photosynthesis declines. Plant
growth in the Southern Hemisphere
later in the year does not make up
for the loss, because most of Earth’s
vegetative cover is in the north.
Ancient air bubbles trapped in
polar ice cores reveal that, over the
past 11,000 years, average CO 2
concentrations were 275–285 ppmv,
but increased sharply from the mid-
19th century. In 1958, the level was
316 ppmv. It rose steadily at a rate
of 1.3–1.4 ppmv each year until the
mid-1970s, then increased by about
2 ppmv each year. By spring 2018 it
had hit 411 ppmv, almost 1.5 times
higher than preindustrial levels. ■19603203403603804001970 1980 1990 2000 2010
YearsCO2 concentration (ppmv)Mauna Loa CO 2 record
(1958 –2015)The Keeling Curve of steadily rising
CO 2 levels is clearly shown on a graph
plotting results from the continuous
monitoring of atmospheric carbon
dioxide (CO 2 ) at Mauna Loa, Hawaii.Bubbles in an ice core provide
a sample of the atmosphere going
back centuries. Scientists measure
the CO 2 in the trapped air bubbles.CO 2 analysis in icecaps
Scientists can measure past
concentrations of carbon
dioxide by analyzing bubbles
of air trapped in Antarctic and
Greenland ice sheets. This
evidence indicates that there
have been several cycles of
variation over the past 400,000
years. These range from lower
readings in the most severe
glaciations—when glaciers
actually formed—to higher
readings during warmer,
interglacial periods. The
increase since the start of the
Industrial Revolution has been
matched by the average global
temperature. This has risen
by 0.13 °F (0.07 °C) per decade
since 1880 and 0.31 °F (0.17 °C)
per decade since 1970.
The Intergovernmental
Panel on Climate Change
(IPCC) warns that unless the
world's governments reduce
greenhouse gas emissions
dramatically, by the year 2100
average temperatures could
be around 7.7 °F (4.3 °C) higher
than they were before the
Industrial Revolution. Such an
increase would cause both a
marked rise in sea levels and
more extreme weather, which
would result in people having
to abandon some regions of
the world entirely.US_240-241_Keeling_Curve.indd 241 12/11/18 6:25 PM