No realistic model climate can warm up by 1.1 C without other aspects of the climate also changing. Other variables besides temperature must change. As the surface and atmosphere warm, the model atmosphere becomes moister, which in turn causes more warming - a positive feedback effect. Snow and sea-ice melt, which enhances warming near the poles. Snow and sea-ice reflect the sun's energy very effectively so, as they melt, more energy is absorbed at the earth's surface.
Feedbacks feed back upon feedbacks, which is why climate modelling is so difficult.
In most models cloud cover increases in a warmer climate. This affects the energy budget in two opposing ways. Clouds reflect sunlight, reducing the amount of energy reaching the surface. Clouds are a major source of uncertainty. If the effects of cloud feedbacks are eliminated, this range is reduced to 1.7-2.3 C.2 Many other feedbacks, particularly those involving chemistry and biology, may also be important.