Climate change is affecting the production of feed on dairy farms. Warming climates also affect the performance of dairy cattle and the interactions between feed production and animal performance. Process level simulation of dairy production systems provides a tool for whole-farm evaluation of the effects of changing weather patterns and increased atmospheric carbon dioxide concentration. Several farm scale models have been used to study the adaptation of dairy production to climate change in Northern Europe, Australia, New Zealand and the United States. The Integrated Farm System Model (IFSM) provides one of the more comprehensive and flexible models of American dairy production systems. IFSM simulates crop growth, harvest and feeding along with animal performance and environmental impacts as influenced by daily weather. Simple routines are also included to represent the effect of atmospheric carbon dioxide on crop growth. The model has been used to explore the impacts of projected climate change over the next century, and simulation results indicate that changing weather patterns can have a very negative impact on farm performance and profitability using current practices. However, adapting to the climate through the use of more suitable crop varieties and species along with appropriate planting and harvest dates can reduce these negative impacts. For some regions, a warming climate can enable greater use of double and triple cropping systems. Keeping land in production throughout the year offers the benefits of reducing nutrient losses to the environment and increasing feed production, but potential adverse effects such as weed and insect control must be maintained. Although current models provide a good foundation, further work is needed to improve the representation of climate effects on crop and animal production. Through continued development, whole farm simulation models provide valuable tools for evaluating, optimizing and adapting dairy production systems to our changing climate.