Creamy vegetable soups can vary really widely in impact on the environment, because creaminess can come either from dairy (relatively high environmental impact), or from alternatives including potatoes, cashews, or soy milk (less greenhouse gas intensive).
For this quick and easy recipe, two potatoes are cooked up with onion in vegetable broth, with broccoli added later. The whole mix goes into your blender (or you can immersion blend), and you can season with salt, pepper, lemon, etc. If you like nutritional yeast, this is a great place for it to introduce a cheesy touch, but it tastes great either way!
See here for the recipe from Bon Appetit. This recipe has you saute the onion in oil, but you can also use water if you are trying to avoid added oil.
Assuming 4 servings, the carbon footprint of this recipe is a climate-cooling 64 g CO2-eq per serving! About half of that footprint comes from the broccoli, with the potato, oil, and onion making up the rest.
Contrast this with a traditional recipe, which has a whopping footprint of 472 g CO2-eq per serving! 89% of the footprint comes from butter and half and half!!