Questions on Carbon Dioxide and Global Warming:
In a stark reminder of humanity's impact on the planet, the levels of carbon dioxide (CO2) in Earth's atmosphere have reached an all-time high. As of mid-2025, atmospheric CO2 concentrations are very close to 429 parts per million (ppm), surpassing levels ever recorded and those experienced in more than three million years.
This alarming trend is the result of a steady and accelerating increase in CO2 concentrations over recent decades, primarily driven by human activities. The burning of fossil fuels, deforestation, and land clearing contribute approximately 7 billion tons of carbon annually into the atmosphere. Natural carbon sinks like oceans, forests, and soils absorb only part of this, resulting in a net buildup of CO2 in the atmosphere—a key driver of global warming and climate change.
The Mauna Loa Observatory, situated at an elevation of 3,397 meters over the Pacific Ocean, provides a record representative of a large volume of the Earth's atmosphere. Data collected here shows a sawtooth pattern, with peaks in late spring, mostly caused by the forests of North America and Eurasia.
The Earth's carbon budget for limiting warming to 1.5°C above pre-industrial levels is critically low—only about 130 billion tonnes of CO2 remain as of early 2025 and are expected to be exhausted in just over three years at current emission rates. This underscores the urgent need for emission reductions.
The longevity of fossil fuel CO2 in the atmosphere means that even if emissions stopped immediately, elevated CO2 and its climate effects would persist for centuries to millennia. If the pace of the last decade continues, carbon dioxide will reach 450 ppm as soon as 2035.
Carbon dioxide, a colorless, odorless greenhouse gas, accounts for two-thirds of the global warming caused by human activities. Scientists at Scripps Oceanography collect CO data at NOAA's Mauna Loa Observatory and other worldwide locations, with monthly average CO levels reported for the Mauna Loa record that makes up the Keeling Curve.
The excess carbon dioxide emitted by human activities stays in the atmosphere for decades to centuries. About half of the excess carbon emitted by human activities every year remains in the atmosphere, overwhelming the natural carbon sinks.
The continued rise in carbon dioxide indicates the likelihood that levels will rise far beyond 420 ppm before they stabilize. The rise in carbon dioxide is unambiguously caused by human activity, principally burning fossil fuels. Rare occasions of CO elevation from volcanic emissions are easily distinguished and removed from the Mauna Loa record.
This ongoing rise in atmospheric CO2 is the core factor driving current global warming trends and poses a severe challenge to stabilizing the Earth's climate system. The implications are significant, with the depleted carbon budget for 1.5°C warming indicating that if emissions continue at the current pace, temperature thresholds linked to dangerous climate impacts will be exceeded rapidly. It underscores the importance of rapid and sustained mitigation efforts.
In the realm of environmental science, the continued rise in atmospheric CO2, a key driver of both global warming and climate change, is primarily attributed to human activities such as the burning of fossil fuels, deforestation, and land clearing. This trend, alarmingly close to 429 ppm as of mid-2025, is closely monitored by scientists using technology, like the data collected at the Mauna Loa Observatory, to better understand ocean acidification and its impacts on the climate-change crisis. The persistence of excess CO2 in the atmosphere, caused by human activities, underscores the urgent need for emission reductions to prevent the exhaustion of the Earth's carbon budget and the escalation of climate-change consequences.
