This lecture covers the definitions of climate and climate change according to the IPCC, as well as the feedback mechanisms related to snow properties. It also delves into past climate variations, ice ages, and their impact on the Earth's climate system. The presentation continues with observed and projected future changes in air temperature, precipitation, soil moisture, cryosphere, and sea level. The lecture concludes by discussing the impacts of climate change on snow cover, water availability, glaciers, river temperature, and electricity production, highlighting the challenges and adaptations needed to mitigate these effects.