Aerosol particles affect the climate directly by scattering solar radiation and by absorbing solar and terrestrial radiation, referred to as aerosol–radiation interactions (ARI). In addition, aerosol particles can affect the climate indirectly by modifying cloud microphysical and radiative properties when acting as CCN and as INPs, referred to as aerosol–cloud interactions (ACI).

This chapter introduces the concepts of radiative forcing (RF) and effective radiative forcing (ERF) in the context of different effects associated with ARI and ACI. For example, the ARI of different aerosol types is discussed in view of the aerosol properties introduced earlier. Similarly, different types of ACI are discussed, including the Twomey effect. By doing so, this chapter synthesizes the knowledge on cloud and aerosol microphysics and thermodynamics gained throughout the textbook, and puts them in perspective of the large-scale impacts of aerosols and clouds on climate, that is the Earth energy budget and the hydrological cycle. The concept of climate feedbacks is introduced, and a perspective on climate interventions is presented.

The chapter describes the basic terminology used in the book, the composition of the Earth system and the principles of climate dynamics. It details the main components of the Earth system (atmosphere, ocean, hydrosphere, cryosphere, biosphere and solid Earth) and processes relevant to understanding climate dynamics. The concepts of climate, climate variability and climate change are discussed in the context of Quaternary climate dynamics. The global cycles of energy, water and carbon and their importance for climate evolution and variability are presented. The chapter introduces the mechanisms behind different types of radiative forcing, climate feedbacks and climate sensitivity. The difference between equilibrium and transient climate responses to different climate forcings is specified. The frameworks of stability and instability are introduced and discussed in application to climate. The relationship between the stochasticity of the Earth system and the predictability of climate change is presented.

The greenhouse effect is a fundamental property of the Earth’s climate that is responsible for keeping the planet warm and habitable for life. The concept of the Goldilocks zone describing the habitability of planets is briefly introduced. Basic concepts in atmospheric physics, such as solar and infrared radiation, are introduced using concepts from everyday life, including an analogy with blankets to explain the greenhouse effect. The two main gases responsible for the greenhouse effect – water vapor and carbon dioxide – are described. The historical background of the discovery of the greenhouse effect, including the very first climate model that predicted global warming (formulated by Svante Arrhenius in the 1890s), as well as the recently uncovered role of Eunice Foote, is presented. Climate feedbacks, which can amplify the global warming, are explained.