Explain the two major processes that drive the normal functioning of the carbon cycle, and then discuss two ways in which humans have negatively impacted this cycle

Question

What will be an ideal response?

Answer 1

Photosynthesis and cellular respiration are the key processes involved in carbon's flux between the biosphere and the atmosphere. Normally carbon (C) contributes only a miniscule amount (0.032%) to the total mass of the lithosphere and atmosphere. During photosynthesis, CO2 is removed from the atmosphere by green plants, algae, and cyanobacteria, where it enters into a series of chemical reactions using light energy to add hydrogen ions and electrons, finally producing energy-rich carbohydrates. All organisms (photosynthetic as well as non-photosynthetic) access this energy through the process of cellular respiration, during which the carbohydrate is broken down, releasing CO2 back to the atmosphere. Deforestation and the burning of fossil fuels have greatly altered this dynamic that has existed between photosynthesis and cellular respiration. Scientists estimate that today, humans harvest approximately 32-40% of global NPP, having replaced natural ecosystems with farmland, cities, and suburbs. This has significantly diminished the amount of carbon stored in Earth's terrestrial ecosystems. For example, when a tropical forest is cleared and converted to pasture, a great amount of CO2 is released into the atmosphere. The burning of fossil fuels has also had a profound effect on Earth's carbon cycle. Between human land use and the burning of fossil fuels, human activities are raising the concentration of CO2 in the atmosphere by about 1% per year.