5000 Cubic Kilometers Of Coal Per Year
Imagine a cube of coal 17 kilometers per side. Now imagine burning one of those cubes each year. If this were a natural phenomenon, people would regard it as a disaster.
We're also burning a 3300 cubic kilometers of oil each year. Imagine a lake of oil 100 meters deep and 1500 kilometers square. Now imagine burning one of those each year.
If an asteroid struck the Earth, or a volcanic caldera erupted, no one would doubt that it could change the climate. Human burning of fossil fuels is a smaller disaster, but it is a disaster, and it will affect Earth's climate.