Carbon dioxide in the atmosphere of Earth

In the atmosphere of Earth, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis, and oceanic carbon cycle. It is one of three main greenhouse gases in the atmosphere of Earth. The concentration of carbon dioxide in the atmosphere reached 427 ppm on a molar basis in 2024, representing 3341 gigatonnes of. This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century. The increase is due to human activity.
The current increase in concentrations is primarily driven by the burning of fossil fuels. Other significant human activities that emit include cement production, deforestation, and biomass burning. The increase in atmospheric concentrations of and other long-lived greenhouse gases such as methane increase the absorption and emission of infrared radiation by the atmosphere. This has led to a rise in average global temperature and ocean acidification. Another direct effect is the fertilization effect. The increase in atmospheric concentrations of causes a range of further effects of climate change on the environment and human living conditions.
Carbon dioxide is a greenhouse gas. It absorbs and emits infrared radiation at its two infrared-active vibrational frequencies. The two wavelengths are 4.26 μm and 14.99 μm . plays a significant role in influencing Earth's surface temperature through the greenhouse effect. Light emission from the Earth's surface is most intense in the infrared region between 200 and 2500 cm⁻¹, as opposed to light emission from the much hotter Sun which is most intense in the visible region. Absorption of infrared light at the vibrational frequencies of atmospheric traps energy near the surface, warming the surface of Earth and its lower atmosphere. Less energy reaches the upper atmosphere, which is therefore cooler because of this absorption.
The present atmospheric concentration of is the highest for 14 million years. Concentrations of in the atmosphere were as high as 4,000 ppm during the Cambrian period about 500 million years ago, and as low as 180 ppm during the Quaternary glaciation of the last two million years. Reconstructed temperature records for the last 420 million years indicate that atmospheric concentrations peaked at approximately 2,000 ppm. This peak happened during the Devonian period. Another peak occurred in the Triassic period.

Current concentration and future trends

Current situation

Since the start of the Industrial Revolution, atmospheric concentration has been increasing, causing global warming and ocean acidification. In October 2023 the average level of in Earth's atmosphere, adjusted for seasonal variation, was 422.17 parts per million by volume. Figures are published monthly by the National Oceanic & Atmospheric Administration. The value had been about 280 ppm during the 10,000 years up to the mid-18th century.
Each part per million of in the atmosphere represents approximately 2.13 gigatonnes of carbon, or 7.82 gigatonnes of.
It was pointed out in 2021 that "the current rates of increase of the concentration of the major greenhouse gases are unprecedented over at least the last 800,000 years".
it is estimated that 2,650 gigatonnes of have been emitted by human activity since 1850, with annual emissions of 42 gigatonnes per year. About 1,050 gigatonnes remain in the atmosphere following absorption by oceans and land.
Some fraction of the fossil carbon transferred thus far will persist in the atmosphere as elevated levels for many thousands of years after these carbon transfer activities begin to subside.

Annual and regional fluctuations

Atmospheric concentrations fluctuate slightly with the seasons, falling during the Northern Hemisphere spring and summer as plants consume the gas and rising during northern autumn and winter as plants go dormant or die and decay. The level drops by about 6 or 7 ppm from May to September during the Northern Hemisphere's growing season, and then goes up by about 8 or 9 ppm. The Northern Hemisphere dominates the annual cycle of concentration because it has much greater land area and plant biomass in mid-latitudes than the Southern Hemisphere. Concentrations reach a peak in May as the Northern Hemisphere spring greenup begins, and decline to a minimum in October, near the end of the growing season.
Concentrations also vary on a regional basis, most strongly near the ground with much smaller variations aloft. In urban areas concentrations are generally higher and indoors they can reach 10 times background levels.

Measurements and predictions made in the recent past

Data from 2009 found that the global mean concentration was rising at a rate of approximately 2 ppm/year and accelerating.
The daily average concentration of atmospheric at Mauna Loa Observatory first exceeded 400 ppm on 10 May 2013 although this concentration had already been reached in the Arctic in June 2012. Data from 2013 showed that the concentration of carbon dioxide in the atmosphere is this high "for the first time in 55 years of measurement—and probably more than 3 million years of Earth history."
As of 2018, concentrations were measured to be 410 ppm.
Measurement techniques

The concentrations of carbon dioxide in the atmosphere are expressed as parts per million by volume. To convert from the usual ppmv units to ppm mass, multiply by the ratio of the molar mass of CO₂ to that of air, i.e. times 1.52.
The first reproducibly accurate measurements of atmospheric CO₂ were from flask sample measurements made by Dave Keeling at Caltech in the 1950s. Measurements at Mauna Loa have been ongoing since 1958. Additionally, measurements are also made at many other sites around the world. Many measurement sites are part of larger global networks. Global network data are often made publicly available.

Data networks

There are several surface measurement networks including NOAA/ERSL, WDCGG, and RAMCES. The NOAA/ESRL Baseline Observatory Network, and the Scripps Institution of Oceanography Network data are hosted at the CDIAC at ORNL. The World Data Centre for Greenhouse Gases, part of GAW, data are hosted by the JMA. The Reseau Atmospherique de Mesure des Composes an Effet de Serre database is part of IPSL.
From these measurements, further products are made which integrate data from the various sources. These products also address issues such as data discontinuity and sparseness. GLOBALVIEW- is one of these products.

Analytical methods to investigate sources of CO₂

The burning of long-buried fossil fuels releases containing carbon of different isotopic ratios to those of living plants, enabling distinction between natural and human-caused contributions to concentration.
There are higher atmospheric concentrations in the Northern Hemisphere, where most of the world's population lives, compared to the southern hemisphere. This difference has increased as anthropogenic emissions have increased.
Atmospheric O levels are decreasing in Earth's atmosphere as it reacts with the carbon in fossil fuels to form.
Causes of the current increase

Anthropogenic CO₂ emissions

While absorption and release is always happening as a result of natural processes, the recent rise in levels in the atmosphere is known to be mainly due to human activity. Anthropogenic carbon emissions exceed the amount that can be taken up or balanced out by natural sinks. Thus carbon dioxide has gradually accumulated in the atmosphere and, as of May 2022, its concentration is 50% above pre-industrial levels.
The extraction and burning of fossil fuels, releasing carbon that has been underground for many millions of years, has increased the atmospheric concentration of. As of year 2019 the extraction and burning of geologic fossil carbon by humans releases over 30 gigatonnes of each year. This larger disruption to the natural balance is responsible for recent growth in the atmospheric concentration. Currently about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere.
Burning fossil fuels such as coal, petroleum, and natural gas is the leading cause of increased anthropogenic ; deforestation is the second major cause. In 2010, 9.14 gigatonnes of carbon were released from fossil fuels and cement production worldwide, compared to 6.15 GtC in 1990. In addition, land use change contributed 0.87 GtC in 2010, compared to 1.45 GtC in 1990. In the period 1751 to 1900, about 12 GtC were released as to the atmosphere from burning of fossil fuels, whereas from 1901 to 2013 the figure was about 380 GtC.
The International Energy Agency estimates that the top 1% of emitters globally each had carbon footprints of over 50 tonnes of in 2021, more than 1,000 times greater than those of the bottom 1% of emitters. The global average energy-related carbon footprint is around 4.7 tonnes of per person.

Roles in natural processes on Earth

Greenhouse effect

On Earth, carbon dioxide is the most relevant, direct greenhouse gas that is influenced by human activities. Water is responsible for most of the total greenhouse effect, and the role of water vapor as a greenhouse gas depends on temperature. Carbon dioxide is often mentioned in the context of its increased influence as a greenhouse gas since the pre-industrial era. In 2013, the increase in CO₂ was estimated to be responsible for 1.82 W m⁻² of the 2.63 W m⁻² change in radiative forcing on Earth.
Earth's natural greenhouse effect makes life as we know it possible, and carbon dioxide in the atmosphere plays a significant role in providing for the relatively high temperature on Earth. The greenhouse effect is a process by which thermal radiation from a planetary atmosphere warms the planet's surface beyond the temperature it would have in the absence of its atmosphere.
The concept of more atmospheric CO₂ increasing ground temperature was first published by Svante Arrhenius in 1896. The increased radiative forcing due to increased CO₂ in the Earth's atmosphere is based on the physical properties of CO₂ and the non-saturated absorption windows where CO₂ absorbs outgoing long-wave energy. The increased forcing drives further changes in Earth's energy balance and, over the longer term, in Earth's climate.