pdq - carbon down greatly from ancient times? because there's less forest fires? kidding.

Trees are carbon neutral - the c02 absorbed while growing is released when it burns...

Not so for the fossil fuels - ever since we've been mining coal and petroleum.. That's co2 stored for millions of years suddenly being released.

Oh and the reason the British started using coal is because the forests were mostly cut down and charcoal for iron smelting was very expensive.
(And the forests had been cut down all over Europe as well)