1. Burning fossil fuels has decreased the total energy available in the world. Fossil fuels are non-renewable, so over humanity's course of fossil fuel usage, fossil fuel supplies get depleted, therefore the total energy in the world decreases.
2. If fossil fuels are discontinued, carbon emissions in the world would vastly decrease, if not completely eliminated. This would slow climate change and global warming. A discontinuation of fossil fuels would require a massive increase in investment into renewables. The scale of renewable energy projects would thus increase. The world's energy collection capacity would also become more dependent on natural variable factors such as wind, water supply and movement, and insolence, and therefore the world's energy supply would become more variable. When fossil fuels are burned, the amount burned and the rate at which usable energy is extracted from it can be controlled.