Assuming I have time, and an audience that isn't too entrenched, I will try to respond with with something that goes like:
Science is both a method of acquiring new knowledge and a largely self-consistent model containing the already acquired knowledge. As we acquire new knowledge, we must update the model.
If our sum of all knowledge was perfect, then we'd never update the model. But, over time, the model tends towards "better than before".
As it is physically impossible to be an expert in all things, at some point you have to trust that the people that have been updating or refining the model where it relates to their specific expertise are largely doing so in good faith and in accordance with the scientific method.
This is not the same as faith. The model can be wrong in places and will get updated over time. This is a process. If you understand the process, then you understand science.
(I sometimes will use different phrasing -- the word "model" throws some people, so instead I'll use "the whole body of knowledge" or something like that.)
