Environmental Science
Atmospheric CO₂
Quick fact
The concentration of atmospheric CO₂ has increased by over 50% since the Industrial Revolution, from about 280 parts per million (ppm) to over 420 ppm today—a level not seen in millions of years.
Why this is interesting
You breathe it out every second, but the tiny amount of CO₂ in the air—just 0.04%—holds the key to Earth's climate. How can such a small fraction cause such enormous changes?
Read the full explanation
Understanding Atmospheric CO₂
Imagine Earth wrapped in a thin blanket of gases. Carbon dioxide (CO₂) is one of many gases, but it's special: it's transparent to sunlight but traps outgoing heat, like a greenhouse's glass. This 'greenhouse effect' is natural and essential—without it, Earth would be frozen. However, by burning fossil fuels (coal, oil, gas) and clearing forests, humans have added huge amounts of extra CO₂ to the atmosphere. This thickens the blanket, trapping more heat and warming the planet. The concentration is measured in parts per million (ppm): for every million air molecules, how many are CO₂? Before 1750, it was about 280 ppm; today it's over 420 ppm. This rise correlates closely with global temperature increase.
A deeper explanation
CO₂ is a long-lived greenhouse gas because its molecular structure absorbs and re-emits infrared radiation, which is the heat Earth radiates after absorbing sunlight. The more CO₂, the more heat stays in the lower atmosphere. This is a positive radiative forcing—an energy imbalance that warms the planet. The carbon cycle naturally moves CO₂ between the atmosphere, oceans, plants, and soil. Human activities inject CO₂ far faster than natural processes can remove it, leading to accumulation. Crucially, the ocean absorbs about 30% of excess CO₂, causing ocean acidification (a separate but related problem). The importance of atmospheric CO₂ lies in its central role in climate feedbacks: warming can release more CO₂ from permafrost and oceans, amplifying the initial change. Understanding it is essential for predicting future climate and designing mitigation strategies like emissions reductions and carbon capture.