Agriculture now occupies ~40% of Earth’s land surface, contributes nearly a quarter of global greenhouse gas emissions, and requires copious input resources, such as water, fertilizer, and land. In particular, ~70% of Earth’s available freshwater resources go towards agricultural production, and in some regions, like South Asia, the proportional use is closer to 90%. Much of this is driven by groundwater extraction – effectively another “fossil fuel” – and there is a need to better understand the environmental and climate impacts, interactions, and consequences of introducing and re-distributing these large amounts of water on Earth’s surface. In this seminar, I will review the current status of global irrigated agriculture and recent advances in understanding and modeling climate-irrigation interactions. I will then describe my specific efforts to model and quantify these interactions using the NASA GISS ModelE earth system model (ESM), a state-of-the-art ESM contributing to major UN climate assessment activities. While the effects of irrigation are global in scope, I will focus my discussion on South Asia, which is arguably the most heavily irrigated place on Earth and where the resulting climate interactions appear increasingly robust and substantial. In particular, my work has shown that current irrigation can weaken the regional monsoonal circulation, cool the land surface (thereby countering regional climate change trends), and alter rainfall distributions in space and time. These findings, which have also been corroborated by a host of other independent studies, have significant ramifications for regional rainfed agriculture, climate adaptation options, and the prevalence of overall climate change signals in South Asia and elsewhere. Lastly, I will discuss key uncertainties and limitations to these studies, and suggest future trajectories for agriculture-irrigation-climate modeling efforts.