The Unavoidable Warmness of Burning
Short version: The Earth adjusts its temperature to send back to space as much energy as is received from the Sun. But, the Sun’s shortwave energy passes easily through the air while some of the Earth’s longwave energy is intercepted by carbon dioxide and other “greenhouse” gases, making the Earth warmer than it otherwise would be, with more warming when more greenhouse gas is added to the air. This warmer air picks up water vapor and melts reflective snow and ice, making the total warming even larger.
Friendlier, but longer version: Think about a factory making cars. Many small parts go in, and a few big cars come out. But, the total amount of stuff going in is very nearly the same as the total amount coming out. If they were very different for very long, the factory would either fill up with parts or run out of them. The factory may need to adjust its rate of making cars to match the rate at which parts arrive, speeding up by hiring more workers when the parts arrive rapidly, and slowing down by sending workers home or out for coffee when parts arrive slowly. Keep reading for the longer version!