Semi-arid ecosystems are increasingly thought to account for a large percentage of interannual variability in land CO₂ uptake, associated with variations in climate drivers such as precipitation. These connections motivate the need for understanding environmental influences beyond tropical rainforest land uptake. It is critically important to investigate connections between the current sensitivity of semi-arid ecosystems to climate as to discern future trends in the strength of the land sink for anthropogenic CO₂. To better inform future projections of carbon balance in earth system models (ESMs), we used a set of Coupled Model Intercomparison Project (CMIP5) ESMs to investigate trends and partitioning of recent CO₂ uptake (1980-2005) from tropical and subtropical regions. We quantified model-to-model differences in net biome productivity (NBP) over semi-arid and tropical regions as well as the sensitivity of NBP to temperature and drought stress for each landcover type. Our results revealed a large spread in NBP among models and between regions. We compared our findings to reanalysis and in situ observations to develop benchmarks for global models and to further probe model-driver relationships in order to constrain long-term projections.