Climate models (also known as Earth system models) integrate our understanding of the basic physics and chemistry of the atmosphere, ocean, and land. They are used to explore scenarios of future climate change and impacts that would result from different levels of future emissions of CO2 and other greenhouse gases. Climate models represent the entire world as a very large number of “grid boxes.” Each box has a single value of every variable that’s predicted (temperature, water, wind, etc) and mechanistic equations are used to advance the model forward in time. We use these models to “predict the past” from 1850 to now in order to evaluate their fidelity, and we use dozens of different models to do the simulations so that we can estimate uncertainties in the predictions. They work very well for the global average, but less well at smaller scales. We can’t predict economic, policy, and technological developments so instead we use a wide range of scenarios to define pathways of future emissions (Representative Concentration Pathways – RCPs). Each of these scenarios is then used to estimate future.