Trees use up the carbon dioxide in the air as a part of photosynthesis. This makes trees the main counter to one of the most common greenhouse gases in the atmosphere. Cutting trees down on such a large scale impedes on how much CO2 is being sucked out of the atmosphere, and releases any the trees might have stored. Thus, it is causing climate change. I'd say that it's worse on that alone.
Deforestation is one of the root causes of climate change global warming itself is therefore it is much else than climate change and global warming and deforestation and humans should fully be blamed and at fault for every inch of treacherous destruction that climate change and global warming has caused.