A) CO2 accumulates. Plants absorb it, they also release it. So does the ocean. And even though the ocean is absorbing more than it releases (making it more acidic), the amount we have been releasing into the atmosphere is still pushing CO2 levels higher and higher. This is easily measured.
B) CO2 historically has not driven temperatures, it's acted as a feedback, making warming temperatures even warmer. Orbital cycles or other factors cause some initial warming, which triggers higher CO2 concentrations, which causes further warming. This is also easily measured in a lab, and shows up in countless lines of observations. CO2 and temperatures have both been higher in the past, but now we're the ones releasing CO2, and we'll have to deal with the results. "Runaway" warming effects are unlikely, but what we expect is going to be plenty expensive enough.
C) Climate models are intended to predict trends, not short-term variation. Longer term trends are easier to predict than random fluctuations, as the random cycles all average out. Only those who don't understand the models (e.g. they're not "all feedback-based models") claim that they're not "working".
D) The effects are already here, you just haven't been looking. They're showing up, not in dramatic unheard-of catastrophes, but in increased likelihood of heat waves, droughts, and fires (in some areas), floods (in other areas), melting glaciers, reduced ice mass (arctic and antarctic). These things aren't new, but they're getting steadily more common, and the costs are already adding up.
Increased CO2 means global average temperatures rise, both on the surface and (more significantly) in the oceans. This has been happening for 150 years, as predicted. More rainfall in some areas, less in others.
There are many studies about the feedback effects of CO2 on plant growth. The overall conclusions are that this will affect the climate, but not very much.
The predictions have been made for decades and longer. They're coming true all around us. Only the deniers refuse to look and see for themselves, insisting that this or that one little thing hasn't changed yet, so nothing could possibly be happening. But a glance at the bigger picture shows overwhelming evidence, which is precisely why there is such a strong consensus among climatologists.