Simulation models play an important role in understanding the causes and consequences of climate change. The Global Carbon Cycling Model (GLOCO), developed by Tetra Tech’s Research & Development department and the Electric Power Research Institute, is a mechanistic model that incorporates mathematical representations of the basic physical, chemical, and biological processes that affect the global carbon cycle.

It simulates the interactions of the global carbon cycle with the cycles of the major nutrients limiting the growth of terrestrial and oceanic biota, and it can be used to predict future atmospheric levels of carbon dioxide (CO₂) given fossil fuel combustion and land use scenarios. GLOCO evaluates Intergovernmental Panel on Climate Change (IPCC) scenarios for fossil fuel combustion from 1990 to 2100 and historical estimates of fossil fuel combustion from 1850 to the present. The model has been used to compare effects of possible management scenarios and to test scientific hypotheses.

Detailed uncertainty analyses have been conducted to determine both the variability associated with model predictions and the relative importance of individual parameters and combinations of parameters in determining model predictions.