Photosynthesis occurs in two stages: light-dependent reactions and light independent-reactions. This last stage is often called Calvin cycle.
The diagram shows reactions occurred in the thylakoid membranes which are located inside the chloroplasts. Therefore, we can identify that these reactions are the light-dependent reactions. During this part of photosynthesis, the energy from the sunlight is absorbed by a pigment called chlorophyl (Chl). Then, it is sequentially coverted into chemical energy stored in the form of molecules: NADPH (nitotinamide adenine dinucleotide phosphate) and ATP (adenosine triphosphate).
Taking shorter showers or turning off the faucet while brushing your teeth can reduce water waste in your home. Only use your dishwasher or washing machine when there is a full load, and switch to energy-saving appliances if possible.
I do believe that it is both naturally occurring and caused by human activity. Although science has proven that it is something that naturally progresses with time, humans have sped up the process. Hope this helps:)
