Biotic influences on climate may be important for sustaining life on Earth. Terrestrial vegetation may contribute by affecting surface-atmosphere fluxes of energy and moisture; the importance of this is examined here by performing two climate simulations with and without vegetation, and using each of the resulting climates as input to a vegetation model. Results suggest that contemporary vegetation increases continental precipitation by 15% while generally reducing temperature extremes, and in a simulation neglecting these effects, the boreal, Amazonian and South-East Asian forests cannot become established. The climatological influences of vegetation increase simulated net primary productivity on land by 28% and allow 69% more vegetation biomass to be sustained, implying that bio-geophysical feedbacks are crucial for maintaining present-day patterns of vegetation.