Underlying proposals to add iron to the ocean as a means to mitigate climate change is the brutal fact that atmospheric carbon dioxide levels have increased precipitously since the 1850s and continue to rise. CO2 levels for the past 1,000 years were derived from ice cores. The inset shows direct atmospheric CO2 observations from Mauna Loa, Hawaii, beginning in 1958. (Adapted from Sarmiento & Gruber. Inset: from C.D. Keeling and the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory)[back]
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