In
their ongoing endeavor to understand our
planet as a whole system, Earth scientists are increasingly using computer
models to help them visualize the causes and effects of climate and
environmental change. These models serve as predictive "tools" that allow
scientists to ask "what if...," and have computers give them answers. An
obvious question to ask nowadays is: What if humans continue to release
greenhouse gases into the atmosphere at a rising rate? How will this affect
global climate? How will the biosphere (life on Earth) respond to these
changes? |
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Actually, these questions were first asked more than 100 years ago by Swedish
physicist Svante Arrhenius. In the latter part of the nineteenth century,
Arrhenius observed humans burning coal and fossil fuels to feed our rapidly
industrializing economies and wondered what effect the resulting carbon dioxide
might have on regional and global temperatures. He then set out to construct by
hand (there were no computers in Arrhenius' day) the first climate model of the
Earth. Based on his calculations, in 1896, Arrhenius predicted that doubling
the amount of carbon dioxide in the atmosphere would raise Earth's average
temperature by about 5°C (Arrhenius 1896). But he estimated that it would take
humans about 1,000 years to release that much carbon dioxide; and if we did, he
and other scientists speculated that the effect would merely prolong the growing
season at higher latitudes--a change that would benefit humans, and farmers in
particular. |
Svante Arrhenius, in 1896, is seated on the table to the right of center.
(Photograph courtesy of the Royal Swedish Academy of Sciences & Physics Today.) |
Although his calculations were surprisingly
accurate, Arrhenius greatly underestimated the rate at which humans would
produce carbon dioxide. Over the last 100 years, carbon dioxide levels have
already risen by 23 percent. Yet, scientists haven't seen a corresponding rise
in temperature (average global temperatures have risen only about 0.5°C, smaller
than Arrhenius expectation by a factor of 2 or 3). Why is this? Because there
are many more variables that influence climate than Arrhenius' model took into
consideration. (Many of these other variables are illustrated and explained
throughout the Earth Observatory.)
Earth scientists are continuing the modeling effort that Arrhenius began. The
main differences today are: (1) scientists discovered many new things during the
course of this century that give them a much deeper understanding of Earth's
climate system, (2) scientists now have computers that enable them to perform
more complex mathematical calculations in a fraction of the time it takes to do
them by hand, and (3) over the last four decades, NASA and its partnering
agencies launched increasingly sophisticated satellite sensors enabling them to
collect more and better data every day on local, regional, and global scales.
Data from ground-based measurements and satellite sensors are fed into the new
models, enabling scientists to visualize the current condition of the Earth's
climate system, as well as to predict where and how it will change in the
future. The accuracy of these models continues to improve over time.
The data used in this study are available in one or more of NASA's Earth Science Data Centers. |
Comparing Arrhenius model results (top) to current measurements of the
Earth's average global temperature (bottom), scientists find there is less
warming today than Arrhenius predicted. The left column in the top table
contains multipliers for the amount of atmospheric carbon dioxide in
Arrhenius' day, while the right column contains the predicted effect on
average global temperature. Arrhenius predicted that doubling carbon
dioxide (or multiplying by 2.0) would raise the Earth's temperature by
5.49°C.
In the bottom table, the middle column shows actual measurements of
relative carbon dioxide (also listing units in "parts per million"), while
the right column shows actual average temperature measurements. Today,
scientists know that carbon dioxide is one of a number of important
variables that influence temperature.
Model data from: Svante Arrhenius, On the Influence of Carbonic Acid
in the Air upon the Temperature of the Ground, Philosophical Magazine 41, 237 (1896)
Global Surface Air Temperatures (GISTEMP) from the Goddard Institute for Space Studies
Carbon Dioxide data from the NOAA Climate Monitoring and Diagnostics Laboratory |