evidence: Causes of the current increase [edit]Anthropogenic CO2 emissions [edit]While CO2 absorption and release is always happening as a result of natural processes, the recent rise in CO2 levels in the atmosphere is known to be mainly due to human (anthropogenic) activity.[18] Anthropogenic carbon emissions exceed the amount that can be taken up or balanced out by natural sinks.[42] Thus carbon dioxide has gradually accumulated in the atmosphere and, as of May 2022, its concentration is 50% above pre-industrial levels.[2] [...] Earlier still, a 200-million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 Ma, by a colossal volcanic outgassing that raised the CO2 concentration of the atmosphere abruptly to 12%, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day.[125] This episode marked the close of the Precambrian Eon, and was succeeded by the generally warmer conditions of the Phanerozoic, during which multicellular animal and plant life evolved. No volcanic CO2 emission of comparable scale has occurred since. In the modern era, emissions to the atmosphere from volcanoes are approximately 0.645 billion tons of CO2 per year, whereas humans contribute 29 billion tons of CO2 each year.[126][125][127][128]