Final answer:
The total anthropogenic carbon input to the atmosphere each year is approximately 100 billion metric tons, with a significant portion coming from the burning of fossil fuels and changes in land use.
Step-by-step explanation:
The correct option is d:
The total anthropogenic input of carbon into the Earth's atmosphere each year is approximately 100 billion metric tons. This staggering amount of carbon is primarily released through the combustion of fossil fuels and deforestation, contributing to rising CO2 levels, which have increased by about 45% since pre-industrial times. The Global Carbon Cycle details that human activities currently emit more than 30 billion tons of CO2 every year, and when considering other sources of anthropogenic carbon, the total is even higher.
The anthropogenic carbon emissions from burning fossil fuels alone are estimated to be around 5.5 billion metric tons of carbon as CO2 annually. Combining this with other sources of anthropogenic carbon releases, including land use changes and industrial processes, leads us to the greater figure. Moreover, evidence shows that such emissions from human activity now exceed those from natural sources such as volcanoes by a vast margin.