We will discuss the current state of the science of climate, its variations and change especially since preindustrial times (part of Anthropocene era). Developing mathematical models of the Earth\u27s climate system and utilizing observations, we investigate the forcing of the climate system which includes natural and human causes; processes and interactions that govern the sensitivity of the system; and impacts ranging from globe-wide to regional spatial scales. The use of model simulations and observational evidence of the past-to-present changes leads to attribution and identification of the mechanisms, including traceability to human-induced activities. The climate system perturbations extend across Earth\u27s physical, biogeochemical and ecosystem domains. Understanding of the past climate and scenarios of mankind\u27s development leads to numerical projections of future climate states, including expectations of changes in extremes of societal concern. Challenges on the science side include improving confidence measures in the outcomes which can then provide improved guidance to technical solutions for adaptation and mitigation. The steady progress in the understanding of the nonstationary climate system has led to reliable science-based inputs for policy decision-making
