Carbonic acid is a type of acid that forms when carbon dioxide gas mixes with water. It is found in fizzy drinks and naturally occurs in our bodies as well. Full definition
This is, in itself, a very serious problem because it leads to the acidification of the oceans, since CO2 forms carbonic acid in water. (realclimate.org)
Warming at high latitudes: This was suspected based upon pretty sound arguments by Arrhenius in 1896, per S. Arrhenius, «On the influence of carbonic acid in the air upon the temperature of the ground», Philosophical Magazine and Journal of Science, London, Edinburgh, Dublin, April 1896. (realclimate.org)
Ocean acidification occurs through the uptake of additional CO2 from the atmosphere, the CO2 converting into carbonic acid as it reacts with seawater. (rstb.royalsocietypublishing.org)