Climate dynamics is very much about exchanges of energy in the Earth System, in particular in the form of heat. An ongoing accounting of where heat goes and its manifestations is a great need and has implications for interpreting the recent past and immediate future. Large uncertainties challenge our ability to infer these changes. Improving the accuracy of our estimates of Earth’s climate state and variability will improve knowledge and understanding of the climate system. This in turn will be translated into improved climate assessments and more reliable climate models, synthesizing the observations, performing attribution of what is happening and why, and in making predictions and projections on all space and time scales.