How does rubbish affect global warming?

Answer 1

If the garbage contains organic matter this will rot, releasing either carbon dioxide (if it rots in the air (aerobicly)) or methane (if it rots without oxygen (anaerobicly)).

Both these gases are greenhouse gases. Methane is an especially powerful greenhouse gas, 21 times more powerful than carbon dioxide.

Trash does not directly affect global warming. Indirectly it is affected by the manufacture and distribution of goods, once purchased and used, becomes trash. To reduce this effect, we need to consume less, so there will be less manufacturing and transporting by burning carbon fuels, and of course we'll use less open land to dispose of our trash. Unfortunately, the trend so far is in the opposite direction. It may take several more generations before this is realized by the general public.