Coal, tar, petroleum, diesel/kerosene, gasoline, natural gas and other crude or distilled petroleum products are concentrated high-energy fuels that come from ancient rocks.
They contain energy molecules made when the sun shone on the earth ages ago. Most fossil energy people use in Vancouver comes from Alberta about 100 million years ago. It travelled through time in the rocks and flowed across space in a pipeline. Fossil fuels are mostly burned in transportation to race though spacetime.
Fossil burning is changing the earth's climate. The carbon that the earth had locked away in rocks is thrown back into the atmosphere and this causes the global climate to heat back up to the temperature it was in the age of the reptiles. This will cause the extinction of the fuzzy little mammals, including humans.
Coal has a lot of carbon and burns slow and very hot. It makes a lot of greenhouse gas and other pollution that damages our lungs and hearts.
Natural gas, on the other hand, burns fast and not so very hot and produces more water vapour and less greenhouse gas in the exhaust.
Gasoline is in the middle. It is greener if it has fresh fuel (ethanol) added to make it burn cleaner to make less local air pollution.
Diesel puts more carbon into the atmosphere than gasoline. If it is mixed with (fresh fuel) vegetable oil and burned in well-tuned engine, it makes less air pollution than dirty gasoline, especially if it is used in a public bus.