1) Photosynthesis is a key part of the natural carbon cycle, in which carbon moves between organic and inorganic forms as producers convert carbon dioxide into organic compounds and consumers and decomposers release it back through respiration.
2) Humans have disrupted this cycle by extracting and burning fossil fuels, releasing carbon that has been locked away for millions of years back into the atmosphere as carbon dioxide.
3) The increasing levels of carbon dioxide in the atmosphere are enhancing the natural greenhouse effect and leading to increased global warming.