Syukuro Manabe, a Japanese scientist working at the US weather agency NOAA, builds in 1967 the first physical-mathematical model capable of quantitatively simulating how solar radiation, atmospheric composition, and surface temperature interact, demonstrating through numerical simulation that increased atmospheric carbon dioxide produces a measurable, predictable rise in the planet's surface temperature — a quantitative physical foundation for the greenhouse effect, until then discussed mainly in theoretical terms since Arrhenius's pioneering work in the 19th century. Klaus Hasselmann, at the Max Planck Institute for Meteorology, develops during the 1970s and 1980s statistical methods that allow rigorous distinction between climate-change signals caused by human activity and the natural noise of short-term climate variability, establishing a methodological framework that allows the observed warming to be scientifically attributed to specific causes. Both works, developed independently and separated by more than a decade, constitute the physical and methodological foundation on which all subsequent climate models used by the United Nations Intergovernmental Panel on Climate Change (IPCC) are built to project future global warming and guide international climate-mitigation policy.