What does unburned fuel do to the atmosphere? And is coal, gas and oil in the ground harmful (being unburned fuel)?

Unburned fuel is also an order of magnitude less in terms of volume than burned fuel. It is also something that’s solvable by better combustion and optimized engines.

Humans are ‘poisoned’ by these things in cities where they live close to thousands of vehicles that pass a few meters away. Inside sometimes a city where this gas accumulates.

And they are not poisoned per se. They lose years of life expectancy and they get preventable diseases. An animal population regulated by predation probably does not notice these differences in life expectancy.

Don’t get me wrong, that’s still a problem, but that’s not an ecological and climatic problem and something that can be addressed after we’ve finished our transition out of the fossil fuel.