Drylands make up approximately 40% of terrestrial ecosystems and hold up to 20% of the global soil organic carbon pool. Most semiarid drylands are, to some extent, grazed by livestock. However, the impact of livestock grazing on carbon cycle dynamics over large spatial and temporal scales remains uncertain, especially as the effects of climate change become more pronounced. Thus far, there has been little work, which has explored how site-specific land management may interact with localized shifts in climate to affect biogeochemical processes in dryland ecosystems globally, particularly in the tropics. We used DAYCENT, an ecosystem simulation model, to explore how grazing intensity and projected climate change may impact biogeochemical dynamics in dryland sites in North America, South America, Asia, and Africa. Our simulation results showed a site-specific biogeochemical response to livestock grazing and climate change, even across ecologically similar dryland systems. In sites that had smaller projected shifts in climate (i.e., the North and South American sites), heavy grazing decreased soil carbon inputs, outputs, and storage. In the other two sites, particularly in the African site, shifts in climate had the largest impact on simulated biogeochemical processes, with a projected 20% decrease in the soil organic carbon pool in the African site by the end of the century. Our study highlights the importance of considering how localized shifts in climate may affect dryland ecosystem function as this may overwhelm land management effects over longer time scales. Our work also suggests that more research is needed to better understand how small-scale, site-specific sensitivity to climate change and land use may influence dryland carbon cycle dynamics at the global scale, particularly in tropical regions.