Most of the global warming is due to the perturbation of which of these cycles?

The correct option is Global carbon cycle.

Global warming is primarily driven by the enhanced greenhouse effect, which occurs when heat-trapping greenhouse gases accumulate in the Earth's atmosphere. Among the various biogeochemical cycles, the global carbon cycle is the most significantly perturbed by human activities, particularly through the burning of fossil fuels (such as coal, oil, and natural gas) and widespread deforestation.

These anthropogenic activities release vast amounts of carbon dioxide (CO₂) into the atmosphere. CO₂ is the primary greenhouse gas emitted by human activities, accounting for the largest share of radiative forcing. This excess carbon dioxide acts like a thermal blanket, trapping infrared radiation (heat) that would otherwise radiate back into space, thereby causing global temperatures to rise.

While the perturbation of other cycles, such as the global nitrogen cycle (which releases nitrous oxide, another greenhouse gas) and the global water cycle (water vapor is a potent greenhouse gas), also affects the climate, their contributions to the current rapid warming trend are not the primary drivers. The water cycle operates largely as a feedback mechanism rather than an initial forcing agent, and nitrogen-based gases contribute far less to total warming than carbon emissions. Therefore, the disruption of the global carbon cycle is the chief contributor to global warming.