The history of the scientific discovery of climate change began in the early 1800s when natural changes in paleoclimate were first suspected and the natural greenhouse effect first identified. In the late 1800s, scientists first argued that human emissions of greenhouse gases could change the climate, but the calculations were disputed. In the 1950s and 1960s, scientists increasingly thought that human activity could change the climate on a timescale of decades, but were unsure whether the net impact would be to warm or cool the climate. During the 1970s, scientific opinion increasingly favored the warming viewpoint. In the 1980s the consensus position formed that human activity was in the process of warming the climate, leading to the beginning of the modern period of global warming science summarized by the Intergovernmental Panel on Climate Change.