Editing Azolla (section)

=== Paleoclimatology and climate change ===
Azolla has been proposed as a [[carbon sequestration]] modality. The proposal draws upon the hypothesized [[Azolla event|''Azolla'' event]] that asserts that 55 million years ago, ''Azolla'' covered the [[Arctic]] – at the time a hot, tropical, freshwater environment – and then sank, permanently sequestering [[Tonne|teratons]] of carbon that would otherwise have contributed to the planet's greenhouse effect. This ended a warming event that reached {{Convert|12-15|C-change|0}} warmer than present-day averages, eventually causing the formation of [[ice sheet]]s in [[Antarctica]] and the current [[greenhouse and icehouse earth|"icehouse period"]].<ref>{{cite web |last=Wang |first=Brian |title=Fix Hothouse Earth Just Like Last Time {{!}} NextBigFuture.com|url=https://www.nextbigfuture.com/2021/08/fix-hothouse-earth-just-like-last-time.html|access-date=2021-08-14|language=en-US}}</ref><ref>{{cite web |date=2018-07-11 |title=Can a tiny fern help fight climate change and cut fertilizer use? |url=https://e360.yale.edu/digest/can-a-tiny-fern-help-fight-climate-change-and-cut-fertilizer-use-azolla |access-date=2021-11-25 |website=Yale E360 |language=en-US}}</ref>

They contribute significantly to decreasing the atmospheric CO<sub>2</sub> levels.<ref name="Speelman-2009"/>