The natural greenhouse effect which has maintained global temperatures within the paleo-climatologically observed range is mainly due to water vapour, with other influences coming from a wide range of variables, such as surface albedo and clouds, that can change according to circumstances. The natural greenhouse effect is much larger than that due to CO2 and the other greenhouse gases whose concentration has a direct anthropogenic influence. Much of the uncertainty in global climate change is due to how these two components of the potential greenhouse effect interact. Climate models all
show positive feedback from the water vapour, which is mainly due to a warmer climate increasing
water vapour content in the atmosphere.
Assessments by the IPCC indicate that human influences extend beyond increases in global average temperature to other aspects of climate.
— very probably contributed to sea level rise during the latter half of the 20th century;
— probably contributed to changes in wind patterns, affecting extra-tropical storm tracks and temperature patterns;
— probably increased temperatures of extreme hot nights, cold nights and cold days;
— more likely than not increased risk of heat waves, areas affected by drought since the 1970s and frequency of heavy precipitation events.