Editing Causes of climate change (section)

==== Carbon dioxide ====
{{Main|Carbon dioxide in Earth's atmosphere}}
[[File:CO2 Emissions by Source Since 1880.svg|thumb|The [[Global Carbon Project]] shows how additions to {{CO2}} since 1880 have been caused by different sources ramping up one after another.]]
[[File:Mauna Loa CO2 monthly mean concentration.svg|thumb|The [[Keeling Curve]] shows the long-term increase of atmospheric [[carbon dioxide]] ({{CO2}}) concentrations since 1958.]]
{{CO2}} emissions primarily come from burning fossil fuels to provide energy for [[transport]], manufacturing, [[Heating#Energy sources|heating]], and electricity.<ref>{{cite web |date=18 September 2020 |last1=Ritchie |first1=Hannah |author1-link=Hannah Ritchie |title=Sector by sector: where do global greenhouse gas emissions come from? |website=[[Our World in Data]] |url=https://ourworldindata.org/ghg-emissions-by-sector |access-date=28 October 2020}}</ref> Additional {{CO2}} emissions come from [[deforestation and climate change|deforestation]] and [[Industrial processes#Chemical processes by main basic material|industrial processes]], which include the {{CO2}} released by the chemical reactions for [[Cement#Chemistry|making cement]], [[Blast furnace#Process engineering and chemistry|steel]], [[Hall–Héroult process|aluminum]], and [[haber process|fertiliser]].<ref>{{harvnb|Olivier|Peters|2019|p=17}}; {{harvnb|Our World in Data, 18 September|2020}}; {{harvnb|EPA|2020|ps=: Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy, as well as greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials}}; {{cite web|title=Redox, extraction of iron and transition metals|url=https://www.bbc.co.uk/bitesize/guides/zv7f3k7/revision/2|quote=Hot air (oxygen) reacts with the coke (carbon) to produce carbon dioxide and heat energy to heat up the furnace. Removing impurities: The calcium carbonate in the limestone thermally decomposes to form calcium oxide. calcium carbonate → calcium oxide + carbon dioxide}}; {{harvnb|Kvande|2014|ps=: Carbon dioxide gas is formed at the anode, as the carbon anode is consumed upon reaction of carbon with the oxygen ions from the alumina (Al<sub>2</sub>O<sub>3</sub>). Formation of carbon dioxide is unavoidable as long as carbon anodes are used, and it is of great concern because CO<sub>2</sub> is a greenhouse gas}}</ref>

{{CO2}} is absorbed and emitted naturally as part of the [[carbon cycle]], through animal and plant [[respiratory system|respiration]], [[Volcano|volcanic eruptions]], and ocean-atmosphere exchange.<ref name="EPAExplainer">{{cite web |date=28 June 2012 |url=http://www.epa.gov/climatechange/science/causes.html#greenhouseeffect |archive-url=https://web.archive.org/web/20170308003615/https://www.epa.gov/climate-change-science/causes-climate-change |archive-date=8 March 2017 |url-status=dead |title=Causes of Climate Change: The Greenhouse Effect causes the atmosphere to retain heat |author=US Environmental Protection Agency (EPA) |publisher=EPA |access-date=1 July 2013}}</ref> Human activities, such as the burning of fossil fuels and changes in land use (see below), release large amounts of carbon to the atmosphere, causing {{CO2}} concentrations in the atmosphere to rise.<ref name="EPAExplainer"/><ref>See also: {{citation |volume=2. Validity of Observed and Measured Data |url=http://www.epa.gov/climatechange/endangerment/comments/volume2.html#1 |title=2.1 Greenhouse Gas Emissions and Concentrations |access-date=1 July 2013 |archive-date=27 August 2016 |archive-url=https://web.archive.org/web/20160827230525/https://www3.epa.gov/climatechange/endangerment/comments/volume2.html#1 |url-status=live }}, in {{harvnb|EPA|2009}}</ref>

The high-accuracy measurements of atmospheric {{CO2}} concentration, initiated by [[Charles David Keeling]] in 1958, constitute the master time series documenting the changing composition of the [[Atmosphere of Earth|atmosphere]].<ref name="le treut 2007 CO2 fingerprint">{{citation |author=Le Treut, H. |chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1s1-3.html#1-3-1 |chapter=1.3.1 The Human Fingerprint on Greenhouse Gases |title=Historical Overview of Climate Change Science |display-authors=etal |access-date=18 August 2012 |archive-date=29 December 2011 |archive-url=https://web.archive.org/web/20111229060759/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1s1-3.html#1-3-1 |url-status=dead}}, in {{Harvnb|IPCC AR4 WG1|2007}}.</ref> These data, known as the [[Keeling Curve]], have iconic status in climate change science as evidence of the effect of human activities on the chemical composition of the global atmosphere.<ref name="le treut 2007 CO2 fingerprint"/>

Keeling's initial 1958 measurements showed 313 parts per million by volume ([[Parts-per notation#Mass fraction vs. mole fraction vs. volume fraction|ppm]]). Atmospheric {{CO2}} concentrations, commonly written "ppm", are measured in parts-per-million by volume ([[Parts-per notation#Mass fraction vs. mole fraction vs. volume fraction|ppmv]]). In May 2019, the concentration of {{CO2}} in the atmosphere reached 415&nbsp;ppm. The last time when it reached this level was 2.6–5.3&nbsp;million years ago. Without human intervention, it would be 280&nbsp;ppm.<ref>{{cite news |last1=Rosane |first1=Olivia |title=CO2 Levels Top 415 PPM for First Time in Human History |url=https://www.ecowatch.com/co2-levels-top-415-ppm-2637007719.html |access-date=14 May 2019 |agency=Ecowatch |date=13 May 2019 |archive-date=14 May 2019 |archive-url=https://web.archive.org/web/20190514143012/https://www.ecowatch.com/co2-levels-top-415-ppm-2637007719.html |url-status=live }}</ref>

In 2022–2024, the concentration of {{CO2}} in the atmosphere increased faster than ever before according to [[National Oceanic and Atmospheric Administration]], as a result of sustained emissions and [[El Niño–Southern Oscillation|El Niño]] conditions.<ref>{{cite web |title=During a year of extremes, carbon dioxide levels surge faster than ever |url=https://www.noaa.gov/news-release/during-year-of-extremes-carbon-dioxide-levels-surge-faster-than-ever |website=Home National Oceanic and Atmospheric Administration |access-date=2 July 2024}}</ref>
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