Hey, sorry, but I think you may have misunderstood me.
Let me try and explain clearer so you might be able to understand this time.
You're saying plants cause global warming... Technically this is true. But what do animals eat? Thats right, plants! And a lot of them. This means that in order to eat animals, you have to make a LOT more plants and use a LOT more water than if you just eat the plants. This is very basic logic. Very basic. There is no way around it - An omnivorous diet causes waaaaaaay more greenhouse gases than a vegan one.
Secondly, if you don't have a brain, even if the plant is producing distress hormones or whatever, it had nothing to process them with. However, even if you were right, again, you have to feed animals plants. Therefore, if you want to minimise damage, you should still go vegan as less plants will be 'harmed'. Again, very basic logic.
Please read the definition again, as clearly you haven't understood it. Perhaps if you still can't understand, you should look up the definitions of 'possible' and 'practical'. Essentially the definition means that you can be vegan without avoiding animal suffering entirely, because it appreciates this may not be POSSIBLE or PRACTICAL. Again, if you don't know what these words mean Google will help.