When the Industrial Revolution began, we also devised many ways of using fossil fuel for oil, coal and gas. The only way to utilize these fuels was by burning. As industrialization continued to expand, so did the practice of fossil fuel burning, thereby releasing gases into the atmosphere. The only problem was that these gases had nowhere else to go and have continued to build up over the years.
By building up, they cause the atmosphere to become more efficient in trapping heat, causing climates to turn warmer. This unnatural or man-made result is referred to as global warming.