Mauna Loa and South Pole Isotopic C13 Ratio (y-axis inverted)

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Description:
The scale of δ¹³C is inverted so that seasonal patterns of CO₂ concentration δ¹³C appear with the same phasing.

Black Dots: Monthly average reduced isotopic ratio of atmospheric carbon dioxide, δ¹³C, versus time at Mauna Loa Observatory, Hawaii (20°N, 156°W) where δ¹³C is in per mil.

Black Curve: The sum of 4 seasonal harmonics and a spline function to the Mauna Loa δ¹³C data. The seasonal harmonics include a linear gain factor, to represent increasing amplitude with time.

Red Dots: Monthly average atmospheric carbon dioxide reduced isotopic ratio, δ¹³C, versus time at South Pole, Antarctica where δ¹³C is in per mil.

Red Curve: The sum of 4 seasonal harmonics and a spline function to the South Pole δ¹³C data. The seasonal harmonics include a linear gain factor, to represent increasing amplitude with time.

Data from Scripps CO₂ Program.
Last updated January 2012.