2.1.1.b (Q101)
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| Language | Label | Description | Also known as |
|---|---|---|---|
| English | 2.1.1.b |
No description defined |
Statements
Observed increases in well-mixed GHG concentrations since around 1750 are unequivocally caused by GHG emissions from human activities. Land and ocean sinks have taken up a near-constant proportion (globally about 56% per year) of CO2 emissions from human activities over the past six decades, with regional differences. (English)
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In 2019, atmospheric CO2 concentrations reached 410 parts per million (ppm), CH4 reached 1866 parts per billion (ppb) and nitrous oxide (N2O) reached 332 ppb. Other major contributors to warming are tropospheric ozone (O3) and halogenated gases. Concentrations of CH4 and N2O have increased to levels unprecedented in at least 800,000 years (very high confidence), and there is high confidence that current CO2 concentrations are higher than at any time over at least the past two million years. (English)
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Since 1750, increases in CO2 (47%) and CH4 (156%) concentrations far exceed – and increases in N2O (23%) are similar to – the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years. (English)
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The net cooling effect which arises from anthropogenic aerosols peaked in the late 20th century. (English)
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