Over millions of years, heat and pressure have converted the remains of ancient forests to fossil fuels. the burning of these fossil fuels has a direct effect on which of the following natural cycles

The natural cycle that would have a direct effect of burning of fossil fuels would be the carbon cycle. The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Hope this answers the question.