We use oil for every modern thing we make, and to power our machinery. As AI begins to express its true hunger, we'll start feeding it from any source we can, including oil and its byproducts. This will exacerbate the oil problem, and accelerate the point where it takes more energy to extract oil than we get from it. From there, things get bad. Real bad.
It will come when our existing generators of electricity are no longer enough to keep up with demand. First, we'll move industries that can be served by both electricity and oil to oil only, and then we'll look to firing up new plants to generate the electricity to meet the rising demand, which will far outstrip the demand we have now. It's a second order effect, but a powerful one.
Of course coal produces the most greenhouse emissions.