203
See also: Environmental feedback loops 224–225 ■ Renewable energy 300–305
■ The Green Movement 308–309 ■ Halting climate change 316–321THE LIVING EARTH
Arrhenius was building on the
work of scientists Joseph Fourier
and John Tyndall earlier in the
19th century. Fourier had wondered
why Earth was not a freezing
wasteland, when the Sun was too
far away to heat it to its current
temperature. He knew that heated
surfaces—such as the surface of
Earth—emit thermal energy, and
that the thermal energy radiating
back into space should result in
colder temperatures on Earth.
Something was regulating the
temperature, and Fourier theorized
that Earth’s atmosphere, made
up of various gases, acted like a
glass box, containing the air
and keeping it warm. Fourier’s
hypothesis, although oversimplistic,
led to the “greenhouse effect”
theory of Earth’s thermal regulation.
John Tyndall was the first to
prove Fourier’s greenhouse effect
hypothesis. His experiments
demonstrated how, when Earth
cools down at night—by releasing
the heat absorbed from the Sun
during the day—atmospheric
gases, especially water vapor,
absorb the heat (radiation) and
cause a greenhouse effect. This
keeps Earth’s temperature at anaverage 59°F (15°C), although in
recent decades human activities
that release greenhouse gases
have pushed this figure higher.
For example, the 10 warmest years
on record have occurred since 1998.Fueling a warming world
By 1904, Arrhenius had become
concerned about the dramatic
increase of CO 2 due to human
actions—primarily through burning
fossil fuels, such as coal and oil. He
correctly predicted the influence
that CO 2 emissions would have on
global temperatures, but eventually
came to the conclusion that an
increase in global temperatures
could have a beneficial effect on
plant growth and food production.
The burning of fossil fuels has,
in fact, increased CO 2 levels more
quickly than Arrhenius expected,
although the planet has warmed
less than he predicted. Scientists
understand now that global
warming is having damaging
effects on people and on the
environment, and will continue to
do so as long as long as emissions
continue to increase. ■The effects of
global warmingSince the end of the 19th
century, carbon dioxide (CO 2 )
in the atmosphere has
increased by about 25 percent,
and the average global
temperature by around 0.9°F
(0.5 °C). Scientific evidence
proves that these changes
have contributed to melting
glaciers and sea ice followed
by rising sea levels—around
8 in (20 cm) since 1880—as
well as damage to coral reefs.
Other phenomena include
longer wildfire seasons, more
extreme weather, and shifts in
the ranges of animals and
plants, leading to disease,
extinction, and food shortages.
The extent to which global
temperatures will increase
depends on whether (and
how rapidly) global CO^2
emissions diminish. Scientists
predict that, at the current
rate, this increase could
range from 0.5°F to 8°F
(0.3 °–4.6 °C) by 2100, with
the greatest warming likely
to occur in the Arctic regions.The Perito Moreno glacier in
Patagonia is one of the few glaciers
that is still growing. The majority
are slowly melting, causing sea
levels to rise worldwide.If the planet were a patient,
we would have treated
her long ago.
Prince CharlesThe atmosphere may act like
the glass of a greenhouse ...
[raising] the mean temperature
of Earth’s surface.
Nils Ekholm
Swedish meteorologist (1848 –1923)US_202-203_Global_Warming.indd 203 12/11/18 6:25 PM