It doesn't take a scientist to understand that the more heat that gets trapped in our atmosphere, and the more glaciers and ice caps that melt, the worse off we are going to be. I don't need a scientist to tell me that California might have 100 years of this, or Sahara Desert might turn into a tropical rainforest. It is enough for me to know that this will have a devastating impact on ecological systems across the globe, and the vast majority of people live near water, and sea levels are rising.
I live in a state where the majority of the population is rural and most people are farmers. I ask climate change deniers if they "believe" in greenhouses, and they look at me like I am silly. Then I explain to them that what we are doing is creating a very big green house. This usually does the trick.