There are different types of uncertainties (natural variability, model and scenario uncertainties) and consequently different ways of how to deal with them.
Models are always a simplification of reality and, therefore, they will never represent reality exactly.
“Uncertainty” has a specific meaning in climate
A climate model ensemble consists of model runs with slight differences in settings or initial conditions, or with different climate models or forcings.
There are many different sources of climate data, all with their advantages and disadvantages.