Geoscience Reference
In-Depth Information
Figure 2.1: The Keeling Curve
Monthly measurements of atmospheric CO
2
concentrations from Mauna Loa, Hawaii, dating back to 1958. The original measurements
were made by Charles Keeling. The record is maintained and updated by scientists with the Scripps Institution of Oceanography. [From
Scripps Institute of Oceanography/NOAA Earth System Research Laboratory.]
These records indicate a steady two-century-long rise in CO
2
concentrations coincident with the
Industrial Revolution, culminating in modern levels that appear unprecedented in hundreds of
thousands of years at least, long before modern humans arrived on the scene. The CO
2
that was
building up in the atmosphere as the Industrial Revolution progressed, moreover, had humanity's
fingerprints all over it; analysis of the carbon isotopes indicated that the source lay in the burning of
fossil fuels. At current rates of fossil fuel burning, CO
2
concentrations, it was estimated, would reach
twice preindustrial levels within about four decades. We'd potentially need to reach back tens of
millions of years, halfway to the age of dinosaurs, to find previous levels that high.
(2) Scientists also knew that this increase in atmospheric CO
2
(and other trace gases produced
by human activity, such as methane) must have a warming effect on Earth's surface. In fact, that had
been known for nearly two centuries. The esteemed French scientist and mathematician Joseph
Fourier (1768-1830) is generally credited with discovery of the warming effect of these gases. Other
great nineteenth-century scientists such as England's John Tyndall (1820-1893) and Sweden's Svante
Arrhenius (1859-1927) helped work out the basic physics and chemistry.
Earth is heated from above by the Sun. The only thing keeping the planet from getting hotter and
hotter is its ability to cool off by emitting its own invisible form of radiation (infrared radiation) to
space. Certain gases in our atmosphere such as carbon dioxide, however, impede this heat loss
mechanism by absorbing a fraction of that radiation and reradiating some of it back down toward the
surface, rather than allowing it to escape to space. This requires Earth's surface to send even more
infrared radiation out to space. And that it can only do by warming up.
This effect, which in some respects resembles how a greenhouse works, is known as the
