ABSTRACT
This chapter summarises the current assessment of Working Group 1 of the International Panel on Climate Change (IPCC) in its Fifth Assessment Report of September 2013, entitled Climate Change 2013: The Physical Science Basis. Based in Stockholm, Sweden, Working Group 1 (WG1) assesses the physical scientific aspects of the global climate system and its change morphologies. The distinction between the two lies in the difference between naturally occurring and long-cycle environmental variability and changing physical circumstance, on one hand, and physically altered environmental conditions that are traceable to the choices humans have made within their environment on the other. Natural and anthropogenic substances and processes that alter the balance of the Earth's energy budget are the drivers of climate change. The strength of specific drivers is quantified as 'radiative forcing' (RF) which is defined as the change in energy flux caused by a change driver, and is calculated at the tropopause or at the top of the atmosphere.
