How Much Carbon Dioxide Is In The Atmosphere?
QUICK ANSWER
Atmospheric carbon dioxide concentrations are currently about 420+ parts per million (ppm), measured continuously since 1958 at NOAA's Mauna Loa Observatory in Hawaii. Pre-industrial levels were about 280 ppm. Atmospheric CO2 increases about 2-3 ppm per year, driven primarily by fossil fuel burning, deforestation, and land use changes.
Atmospheric carbon dioxide concentration is one of the most important measurements in climate science. The continuous measurements since 1958 produce the famous Keeling Curve, showing both the steady annual rise and seasonal oscillations as plants take up CO2 during growing seasons. Understanding current levels and trends is essential for understanding climate change, since CO2 is the most important human-influenced greenhouse gas.
What is the current CO2 level?
Atmospheric CO2 is currently around 420+ parts per million (ppm), tracked continuously by NOAA's Global Monitoring Laboratory tracking of atmospheric CO2. The exact monthly value rises and falls slightly with seasons but trends upward at about 2-3 ppm per year. Pre-industrial CO2 levels were about 280 ppm, meaning concentrations have risen by about 50% due to human activities. The Mauna Loa Observatory in Hawaii has measured CO2 since 1958, providing the most famous and longest continuous record of any greenhouse gas. Similar measurements are made at dozens of monitoring stations worldwide.
How is atmospheric CO2 measured?
Atmospheric CO2 is measured through infrared spectroscopy. Sample air is passed through a chamber where infrared light at specific wavelengths is shone through. CO2 molecules absorb light at characteristic wavelengths, and the amount of absorption indicates the concentration. The Mauna Loa Observatory's location at 11,000 feet on a Pacific volcano produces measurements representative of the well-mixed atmosphere far from local pollution sources. Satellite measurements from instruments like NASA's OCO-2 also map CO2 distribution globally. Ice cores provide historical CO2 records going back hundreds of thousands of years.
How has CO2 changed historically?
CO2 concentrations have varied throughout Earth's history but were stable around 280 ppm for the 10,000 years before the Industrial Revolution. Ice core records show CO2 has oscillated between roughly 180 ppm during glacial periods and 280 ppm during warm interglacial periods over the past 800,000 years. The current level of 420+ ppm is higher than at any point in the past 800,000 years and probably higher than the past few million years. The rate of increase (2-3 ppm per year) is unprecedented in geological records, far faster than natural changes.
Why does CO2 vary seasonally?
Atmospheric CO2 oscillates seasonally because of plant activity in the Northern Hemisphere. From May to September, deciduous forests and other Northern Hemisphere vegetation photosynthesize actively, pulling CO2 from the atmosphere. From October to April, plant activity slows and decay releases CO2. The Northern Hemisphere has more land and more vegetation than the Southern Hemisphere, so the global signal follows northern seasons. The seasonal oscillation is about 5-8 ppm peak-to-peak, but the long-term trend keeps rising due to human emissions, producing the sawtooth pattern of the Keeling Curve.
Atmospheric CO2 is currently about 420+ parts per million, up from 280 ppm before the Industrial Revolution. Tracked continuously at Mauna Loa since 1958, CO2 concentrations rise about 2-3 ppm per year due to fossil fuel burning and land use changes. The current level is unprecedented in the past 800,000 years and is driving climate change.
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