evidence: About a billion years from now, all surface water will have disappeared and the mean global temperature will reach 70 °C (158 °F). [...] Since the start of the 20th century, the global mean surface temperature of the Earth has increased by more than 0.7°C and the rate of warming has been largest in the last 30 years. [...] Currently, surface temperatures are rising by about 0.2 °C per decade.