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(A) Variation in the isotopic discrimination of land photosynthesis for three variable Δ scenarios, each of which was optimized to match the rate of change in δ13C since 1978. (B) Measured vs. modeled δ13C. Ice core data sources: WAIS divide (4), Law Dome (53), and Siple Station (54). All runs initiated at a value of δ13C = −6.4‰ in year 1765. In the model–data comparison, trends are significant but not absolute differences.
