The gas released by burning fossil fuels is primarily carbon dioxide (CO2). When fossil fuels such as coal, oil, and natural gas are combusted for energy, they release CO2 as a byproduct. This process occurs in power plants, vehicles, and various industrial processes. Carbon dioxide is a significant greenhouse gas, contributing to climate change and global warming by trapping heat in the atmosphere. The increase in CO2 levels due to fossil fuel combustion is a major environmental concern, prompting efforts towards sustainable energy alternatives like wind, solar, and hydroelectric power to mitigate climate impact and reduce emissions.