Ecology / Oxygen Cycle — UPSC Mains Model Answer

Forests contribute to net oxygen production through photosynthesis, but their gross contribution is partially offset by respiration and decomposition within the same ecosystem. Large-scale deforestation reduces net photosynthesis, diminishing oxygen output while simultaneously releasing stored carbon. However, the net atmospheric oxygen impact of deforestation alone remains modest given the vast size of the atmospheric oxygen reservoir.

Burning fossil fuels consumes oxygen and releases carbon dioxide, causing a measurable but extremely small decline in atmospheric oxygen — from roughly 20.946% to approximately 20.940% over decades of industrialisation. This change is scientifically detectable but far too marginal to push levels below 20%, making Statement II factually overstated and misleading from a policy-communication standpoint.

Marine phytoplankton are estimated to generate roughly half of Earth's total oxygen production, making them quantitatively more significant than terrestrial forests on a global scale. Ocean warming, acidification, and nutrient stratification threaten phytoplankton biomass and diversity. A sustained decline in phytoplankton populations would therefore carry a proportionally greater impact on atmospheric oxygen than equivalent losses of terrestrial vegetation.

Effective oxygen-cycle governance requires integrating ocean health into climate policy alongside forest conservation. Instruments such as marine protected areas, regulation of ocean-warming drivers through emissions reduction, and monitoring frameworks for phytoplankton trends must complement land-based afforestation programmes to address both production systems coherently.