 A climate is a property of a climate system, but there are different views on what sort of property it is. According to what might be called actualist views, a climate is defined by actual conditions in the climate system. Narrower actualist definitions, which have their roots in climatology (see  Section 1),  reference weather conditions only. For example, the climate of a region is often defined as its average weather conditions, or the statistical distribution of those conditions, when long time periods are considered (Houghton 2015: 2; IPCC-glossary: 1450). The standard period of analysis, set by the World Meteorological Organization, is 30 years, defining a “climate normal” for a region. Given recent rates of change in climate system conditions, however, some climate scientists suggest that climate normals should now be defined over much shorter periods (Arguez &amp; Vose 2011). Broader actualist definitions of climate reference conditions throughout the climate system. The Intergovernmental Panel on Climate Change (IPCC), for example, gives a broader definition of climate as “the state, including a statistical description, of the climate system” (IPCC-glossary: 1450). These broader definitions emerged in the second half of the twentieth century in connection with increased efforts to understand, with the help of physical theory, how climates in the narrower sense are maintained and changed via atmospheric, oceanic and other processes. These efforts in effect marked the emergence of climate science itself (see  Section 1).