September 3, 1999 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? |
Part 1: Modeling the Land Biosphere | |
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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. |
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 |