Editing IPCC:AR6/WGI/Chapter-5 (section)

=== The Human Perturbation of the Carbon and Biogeochemical Cycles ===

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'''Global mean concentrations for well-mixed GHGs (CO''' <sub>2</sub> ''', CH''' <sub>4</sub> '''and N''' <sub>2</sub> '''O) in 2019 correspond to increases of about 47%, 156%, and 23%, respectively, above the levels in 1750 (representative of the pre-industrial era)''' ( ''high confidence'' ''').''' Current atmospheric concentrations of the three GHGs are higher than at any point in the last 800,000 years, and in 2019 reached 409.9 parts per million (ppm) of CO <sub>2</sub> , 1866.3 parts per billion (ppb) of CH <sub>4</sub> , and 332.1 ppb of N <sub>2</sub> O ( ''very'' ''high confidence'' ). Current CO <sub>2</sub> concentrations in the atmosphere are also unprecedented in the last 2 million years ( ''high confidence'' ). In the past 60 million years, there have been periods in Earth’s history when CO <sub>2</sub> concentrations were significantly higher than at present, but multiple lines of evidence show that the rate at which CO <sub>2</sub> has increased in the atmosphere during 1900–2019 is at least 10 times faster than at any other time during the last 800,000 years ( ''high confidence'' ), and 4–5 times faster than during the last 56 million years ( ''low confidence'' ). {5.1.1, 2.2.3; Figures 5.3, 5.4; Cross-Chapter Box 2.1}

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