The Carbon and Climate Problem: Bathtub Analogy
Think of the atmosphere as a bathtub and carbon emissions as the water filling the tub
(Figure 1). Earth’s atmosphere contains about 800 billion tons of carbon dioxide. Fossil
fuel combustion adds about 8 billion tons of carbon per year. Ocean and land biospheres
can soak up some of the carbon in the atmosphere, but only about half of the carbon we
emit to the atmosphere every year. As a result, the level of carbon in the tub is rising
because the remaining carbon (roughly 4 billion tones per year) accumulates in the
atmosphere.
In pre-industrial times, the atmosphere contained only about 600 billions tons of carbon,
compared with the roughly 800 billion tons in the atmosphere today (Figure 2).
Atmospheric carbon changes of a similar magnitude (200 billion tons) have meant the
difference between Ice Ages and the relatively familiar climate of the recent past.
Almost every year, the fossil fuel tap opens wider. Forecasts and trend data indicate that
in 50 years, we’ll be adding carbon into the atmosphere at twice today’s rate. We expect
the amount of carbon in the atmosphere will reach 1200 billion tons, double the preindustrial value, even before the turn of the century. The Earth’s temperature will
continue to rise at an unprecedented rate, unless we do something to get off this path.
Work Cited
Hotinski, R. (2011). Stabilization Wedges: A Concept & Game. The Carbon
Mitigation Initiative at Princeton University. <cmi.princeton.edu/wedges>
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