This landmark IPCC report states that there is "a discernible human influence on global climate" despite many uncertainties. The report provides evidence that the Earth's average surface temperature has increased by about 0.3 to 0.6°C since the end of the 19th century. This is an unprecedented warming which most likely cannot be attributed to natural causes only.
For the IPCC mid-range emissions scenario, the models predict based on the "best estimate" of climate sensitivity an increase in global mean surface temperature of about 2°C by 2100 compared to 1990.
This scientific finding encouraged many governments to intensify negotiations on what would later become the Kyoto Protocol in 1997.