As of March 2024, the monthly average concentration of CO2 reached a new record high of 425.22 parts per million (ppm), marking an increase of 4.7 ppm over March 2023. By the latest measurement, levels had further escalated to 427.48 ppm.[5] This continuous increase in CO2 concentrations is a clear indicator of ongoing global environmental stress, primarily driven by the burning of fossil fuels, which is the principal cause of this rise and also a major contributor to climate change.[6] Other significant human activities that emit CO2 include cement production, deforestation, and biomass burning.


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 (2,347 cm−1) (asymmetric stretching vibrational mode) and 14.99 μm (667 cm−1) (bending vibrational mode). CO2 plays a significant role in influencing Earth's surface temperature through the greenhouse effect.[7] Light emission from the Earth's surface is most intense in the infrared region between 200 and 2500 cm−1,[8] 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 CO2 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.[9]


The increase in atmospheric concentrations of CO2 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 CO2 fertilization effect. The increase in atmospheric concentrations of CO2 causes a range of further effects of climate change on the environment and human living conditions.


The present atmospheric concentration of CO2 is the highest for 14 million years.[10] Concentrations of CO2 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.[2] Reconstructed temperature records for the last 420 million years indicate that atmospheric CO2 concentrations peaked at approximately 2,000 ppm. This peak happened during the Devonian period (400 million years ago). Another peak occurred in the Triassic period (220–200 million years ago).[11]

Data from 2009 found that the global mean CO2 concentration was rising at a rate of approximately 2 ppm/year and accelerating.[25]

[24]

The daily average concentration of atmospheric CO2 at first exceeded 400 ppm on 10 May 2013[26][27] although this concentration had already been reached in the Arctic in June 2012.[28] 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."[29]

Mauna Loa Observatory

As of 2018, CO2 concentrations were measured to be 410 ppm.[30]

[24]

The burning of long-buried fossil fuels releases CO2 containing carbon of different to those of living plants, enabling distinction between natural and human-caused contributions to CO2 concentration.[37]

isotopic ratios

There are higher atmospheric CO2 concentrations in the Northern Hemisphere, where most of the world's population lives (and emissions originate from), compared to the southern hemisphere. This difference has increased as anthropogenic emissions have increased.

[38]

Atmospheric O2 levels are decreasing in Earth's atmosphere as it reacts with the carbon in fossil fuels to form CO2.

[39]

Carbon budget

Global temperature record

Current global map of carbon dioxide concentrations.

(NASA; 13 December 2016)

Global Carbon Dioxide Circulation

(NASA; 17 November 2014)

Video (03:10) – A Year in the Life of Earth's CO2