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The Keeling Curve
The sawtooth pattern is the northern hemisphere's forests breathing: taking up carbon in summer and releasing it in winter. It is the planet's respiration, measured. The underlying rise — from 315 ppm in 1958 to over 420 today — is the single measurement that made global warming a fact rather than a model. Keeling had to fight for funding repeatedly; the series was nearly broken in 1964 and again in the 1970s.
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