Often abbreviated to just AGW. This is global warming which has been caused by human activity in addition to natural global warming.
The science around this is difficult to prove, as identifying a clear indicator of the human contribution which is independent of multiple natural causes is very hard to do in reality. The human element to global warming needs to be clearly and precisely measured against a background of natural global warming that has been occurring since the last ice age. Given the, until recent, lack of good direct measurement of the climatic system; a lot of dependence has been place on proxy measurements, which often have high inherent error and many secondary effects that need to be taken into account.