According to environmental groups like Greenpeace, fast fashion is a big factor in climate change. The process of producing clothes releases carbon dioxide into the air, which contributes to global warming. And a lot of fast fashion clothing is made of materials like polyester, which can take up to 200 years to break down. That means if you buy a shirt today and throw it away next month, it may wind up in a landfill for the next two centuries. The gases created by landfills (basically enormous garbage dumps covered by dirt) also contribute to climate change.