We've gotta start somewhere

Figure 1 - A map of Europe showing an imagined alarmist coastline plan if all The Earth's ice were to melt, which at current rates it is estimated could occur within 5000 years.
Map: National Geographic

In this blog I plan to look at the effects eustatic sea level fluctuations have had on planet earth and its inhabitants, from the naturally induced fluctuations of the Late Quarternary to the more alarming increase in sea level since the mid 1800’s, (The recent Anthropocene - if you believe we have entered a new epoch of human influence) and even to the future, looking at possible outcomes of the predicted rising.

First i'll set the scene by explaining some of the main factors that cause such fluctuations in global absolute sea level over the earths history. Eustatic sea level is mainly influenced by changes in the volume of water found in the oceans. It is however also affected by morphological changes to the earth’s surface resulting from tectonics, subsidence, glacial isostatic rebound and sedimentation, which alter the volume of the ocean basins which contain the water.

There are two major factors which cause the volume of ocean water to change on a global scale, the amount of water locked up in oceans vs. other reservoirs, and the temperature of the ocean at the time.

The thermal expansion coefficient of H₂O is such that when placed at higher temperatures the volume of a body of water expands, therefore when earth experiences an increase in surface temperature the oceans will be heated and the water will expand accordingly, greater volume of water in the oceans means a higher eustatic sea level (other factors remaining the same).

An increase in surface temperature also leads to the melting of glaciers and ice sheets, causing a greater percentage of the earth’s water to be held in the oceans relative to other reservoirs, increasing eustatic sea level. Anthropogenic factors such as land hydrology can also affect the relative proportion of water storage in oceans against land reservoirs, however this occurs on a more regional scale and therefore its effects are generally felt over shorter timescales.

Although humans may not be directly pumping the vast majority of water into the oceans that is causing sea levels to rise so drastically, we are responsible for the intense period of warming The Earth is currently experiencing (although that is another debate for another blog). It is this warming that is causing modern eustatic sea level rise that is threatening so many of earth's present day ecosystems and societies.

I’ll end this post with a link to the 2007 IPCC report on climate change, specifically the chapter titled; Observations: Oceanic Climate Change and Sea Level., which goes into the subject of what causes sea level rise in more depth and is a good read if you are interested in the subject of sea level rise or oceans in general.

References

Bindoff, N.L., J. Willebrand, V. Artale, A, Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. Le Quéré, S. Levitus, Y. Nojiri, C.K. Shum, L.D. Talley and A. Unnikrishnan, 2007: Observations: Oceanic Climate Change and Sea Level. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Pirazzoli, P (1996). Sea-level changes - The Last 20000 Years. Chichester: John Wiley & Sons. p5-15.