Carbon dioxide is naturally present in the atmosphere as part of the earth's carbon cycle. human activities are altering the carbon cycle, by adding more co2 to the atmosphere and by influencing the ability of natural sinks, like forests, to remove co2 from the atmosphere. while co2 emissions come from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution. consider the graph above. notice the trend in atmospheric carbon dioxide as recorded at recording stations over antarctica. hypothesize how the schematic of the carbon cycle might change if urbanization and deforestation continues unchecked. a) both the carbon dioxide sinks and the carbon dioxide outputs will increase so the numbers should reach equilibrium. b) the photosynthesis carbon sink will decrease in gigatons; the carbon dioxide output due to combustion will increase. c) all of the carbon dioxide sinks will decrease in gigaton amounts; the carbon dioxide output due to combustion will increase. d) carbon dioxide outputs due to combustion of fossil fuels continues to increase; the rate of photosynthesis will also continue to increase to accommodate this.