A “Make a Difference” Experiment to Assess the Value of ARM Data in Carbon Cycle Models

Atmospheric Radiation Measurement (ARM) Program data include many of the measurements needed by carbon modelers to predict carbon dynamics in terrestrial ecosystems. How much difference, if any, would using ARM measurements rather than any of several synthetic climate generators typically used by carbon modelers make in estimates of respiration and productivity predicted by carbon models? We designed a “make a difference” simulation experiment to compare differences in carbon flux predictions based on synthetic input data with predictions based on historical measurements taken from the ARM archive. The experimental design used alternative data sources that an intelligent carbon modeler might employ in the absence of ARM measurements. Because “true” carbon fluxes are unknown, our experiment examined only the magnitude of differences created when the same carbon model, BiomeBGC, was driven with synthetic climate rather than actual ARM measurements. The position of ARMderived measurements within a population distribution of synthetic records provided a non-parametric test of significance.