Abstract: The controversial points of views of IPCC and NIPCC are reviewed. IPCC holds that the global warming is caused by the anthropogenic effect. However, NIPCC says, nature, not human activity, rules the climate. Observations of temperatures in the last one hundred years or so support the hypothesis of the anthropogenic impact, but natural factors such as solar activity, volcanism, and thermohaline circulation also take part in the modulation of temperature changes, especially in frequency band of inter-decadal variability. There is pervasive evidence for solar or cosmic ray forcing of the climate in time scale of last 1 ka to 10 ka, which proves that solar activity played an important role in the formation of MWP or LIA, and the cold events over the North Atlantic in the Holocene, though the mechanism responsible for the linkage of solar activity to the earth’s climate is to be understood. Recently, the point of view that galactic cosmic rays can impact low clouds, thus resulting in climate cooling, is prevailing. However, its influencing mechanism is remained to be further investigated.