Flooding Induced by Rising Atmospheric Carbon Dioxide

A direct consequence of rising CO2 is increasingly devastating flooding, because deciduous plants deploy fewer stomates each year as the atmospheric CO2 supplies more carbon for photosynthesis. When plants transpire less, more water runs off in streams and floods. Here we quantify this effect with highresolution observations of changing density and size of stomates of a mesic tree, Ginkgo, since 1754. The observed decline in maximum potential transpiration corresponds with rising water levels in the Mississippi River and represents a potential transpiration decline from 1829 to 2015 of 18 mL s–1 m–2: a reduction of 29%. Rising atmospheric CO2 and declining transpiration promote flooding, which handicaps lowland cultivation and renders irrelevant insurance and zoning concepts such as the 100-year flood.