400 ppm of CO2: How will sea-level respond?

Contributor(s): 
June 13, 2013

We are currently on the eve of a world with ~400 parts per million (ppm) of atmospheric carbon dioxide (398.35 ppm as of May 2nd, Mauna Loa Observatory). How global climate, sea-level and ecosystems will respond to this level of CO2 level is a key question for global change research. Recently, Foster and Rohling (2013) looked back into Earth’s geological history to explore the relationship between atmospheric CO2 and global sea-level.

CO2 and sea-level data for teh past 40 million years based on a variety of reconstruction methods show a strong sigmoidal relationship between the two variables. This strongly supports a key role for CO2 on Earth’s climate and sea level. Using this sigmoidal model, they predict that the “likely” (68 probability) sea-level response to a 400-450 ppm CO2 is about 9 meters. However, it’s important to note that geological and geochemical CO2 and sea-level reconstruction approaches have inherited errors. The regression error near 400 ppm of CO2 is particularly large, because most of the data are from the late Miocene to Pliocene (~14 to 3 million-years ago), a time period that is less well constrained. Moreover, geological records provide an “equilibrium” response of the Earth to changing greenhouse gas forcing — a condition that can take thousands of years to establish. 

Citation:

G. L. Foster, E. J. Rohling, Relationship between sea level and climate forcing by CO2 on geological timescales. Proc. Natl. Acad. Sci. 110, 1209 (2013).