Two independent programs have collected and analyzed atmospheric CO 2 samples from Point Barrow, Alaska, for radiocarbon content ( 14 C) over the period [2003][2004][2005][2006][2007]. In one program, flask collection, stable isotope analysis, and CO 2 extraction are performed by the Scripps Institution of Oceanography's CO 2 Program and CO 2 is graphitized and measured by accelerator mass spectrometry (AMS) at Lawrence Livermore National Laboratory. In the other program, the University of

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... fornia, Irvine, performs flask collection, sample preparation, and AMS. Over 22 common sample dates spanning 5 yr, differences in measured  14 C are consistent with the reported uncertainties and there is no significant bias between the programs.