Based on the current state of science, technology, policy development and implementation, the probability of meeting emissions targets is doubtful. This means that global temperature rises will, in all probability, exceed the recommended levels, most likely substantially and earlier than projected. The consequent changes in planetary geo-physics and meteorology will be substantial.
An energy transition refers to a major structural shift in energy systems. There have been several such historical transitions - bio-fuels, such as wood, to water and wind energies and then to fossil fuels. In its current usage, it is used to describe the attempt to replace fossil-based systems of energy production and consumption with renewable energy sources.