What Happens When Oxygen Levels Change Due to Global Warming

Oxygen seems to exist infinitely in the air. We learned in school that oxygen makes up roughly 21% of our atmosphere. But what would happen if this ratio were to shift?

Global warming is changing the concentration of atmospheric oxygen. Burning fossil fuels directly consumes oxygen from the air on a continuous basis. However, an even greater problem lies in the oceans. As global warming raises ocean temperatures, gas solubility drops, causing dissolved oxygen in the water to plummet. Marine phytoplankton—responsible for producing nearly 70% of the Earth's oxygen—face severe threats of extinction due to rising temperatures and disrupted ocean circulation. Coupled with severe droughts and massive wildfires destroying forests (often called the "lungs of the Earth"), the planet's entire oxygen replenishment loop is under serious strain.

If the oxygen ratio drops significantly, complex organisms will gradually vanish. Only certain anaerobic microorganisms and resilient mutants capable of surviving in oxygen-deprived environments will endure—a scenario tantamount to an apocalypse for humanity.

Conversely, a sharp rise in oxygen levels would be equally disastrous. If atmospheric oxygen were to rise past the current 21% to 25–35% or higher, the planet would spiral completely out of control.

First, global wildfires would become an everyday reality. Higher oxygen levels drastically accelerate combustion, making even wet wood ignite easily. A single lightning strike could turn forests across an entire continent into ash.

Second, mammals would face extinction, and insects would rule the Earth. High oxygen concentrations flood human and mammalian bodies with cell-damaging reactive oxygen species (ROS), leading to oxygen toxicity. In contrast, arthropods—which breathe directly through a system of tracheal tubes—would experience maximized respiratory efficiency. Much like during the Carboniferous Period, giant insects such as massive dragonflies and millipedes would dominate the ecosystem.

Earth's history clearly demonstrates how shifting oxygen levels shape life. Oxygen has always been the fundamental master key determining the trajectory of ecosystems. Around 4.6 billion years ago, the early Earth's atmosphere had virtually 0% oxygen. However, roughly 2.4 billion years ago, the Great Oxidation Event occurred with the emergence of cyanobacteria—photosynthetic microorganisms. As oxygen (which was toxic to existing life at the time) accumulated, most anaerobic organisms went extinct. Yet this ordeal ultimately gave rise to the ozone layer, blocking harmful ultraviolet radiation and paving the way for complex multicellular organisms.

Later, during the Carboniferous Period of the Paleozoic Era around 300 million years ago, oxygen levels surged to an astounding 35%, ushering in the era of giant insects. After countless cycles of rise and fall, the atmosphere eventually settled into the delicate 21% balance that provides the most stable environment for life today.

What must we do to protect this delicate balance? As Earth's history shows, the 21% oxygen ratio is no coincidence—it is the result of 4.6 billion years of intricate biological and planetary regulation. What steps should we take to preserve it?

First, we must accelerate the transition to decarbonization. Reducing fossil fuel usage directly cuts oxygen consumption while curbing carbon emissions.

Second, we must protect marine ecosystems and forests. To safeguard phytoplankton and tropical rainforests—the primary oxygen producers—we need to stop ocean pollution and invest heavily in global reforestation efforts.

The air we breathe is by no means infinite. I hope today's discussion serves as a gentle reminder of just how precious our planet truly is. Thank you.

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