We also can't model every single one of the atoms splitting in a nuclear reactor core, but thanks to stats and models, we can predict how they behave to very high precision.

Knowing whether or not anthropogenic greenhouse gas emissions impact global climate can be reasonably achieved with some modeling assumptions.

We may not be able to predict the weather in each location for the indefinite future, but we certainly can and do understand the general impact of bringing billions of tonnes of new greenhouse gas into a system.