The history of global climate on the earth during these 600 million years is presented based on the oxygen isotope data of fossil shells. The paleoclimatic curves clearly show the cyclic changes with different frequencies, such as, glacial-interglacial cycle of 0.1 Ma and Fischer-Arthur cycle of 32 Ma, and Greenhouse-icehouse cycle of 300 Ma. Today is located in the interglacial period of icehouse state. There are essential differences of the environmental systems and conditions between the greenhouse and icehouse states. The greenhouse state characterized by no continental ice sheets, simple climatic zones, more carbon dioxide in atmosphere, small annual temperature range, warmish and humid poles, high sea level, wide continental shelves, low latitudinal and vertical gradients of seawater temperature, warm oceans, slow circulation of bottom currents, anoxic oceans, abundant marine organisms, black shale deposition of oil raw material, sulfide deposits on oceanic ridges, manganese deposits on continental shelves, active magmatism, first spreading, magnetic quiet and active orogeny. A modern greenhouse warming was also compared with the warming after the “Younger Dryas Event” in the postglacial age.