This technical report is aimed at introducing the climate system and simple climate models (SCMs). This report has two objectives namely: to explain how SCMs work, the processes that are induced in them, what their strengths and weaknesses are in relation to more complex models and the purposes to which they are applied. The second objective is to fully document the procedures and assumptions used to generate the trace gas concentration, global mean temperature change and global mean sea level rise projections. This report also attempts to reflect the importance of this document as tools for scientific and policy analysis. It further extensively analyses the global climate and climate system specifically looking at human effects to the composition of the atmosphere and cloud, surface and dynamical interactions between clouds, land surface, oceans and atmospheric motions. This analysis is further made by an assessment of radiative forcing, fast and slow feedbacks, climate sensitivity and regional climate response. The report also examines the hierarchical structure of the atmosphere and ocean climate models, carbon cycle models, atmospheric chemistry and aerosols model, models of ice sheets, computes the rise in sea level and utilization of simple and complex models in policy development. This report further describes the simple climate models used in the IPCC Second Assessment Report and makes a comparison of surface temperature changes and ocean thermal expansion as stimulated by atmosphere-ocean general circulation models (AOGCMs) and SCMs.