sustained increase in concentration far surpass their expected natural fluctuation (EPA, 2012). Since the Industrial Revolution, the burning of fossil fuels has substantially increased amounts of carbon dioxide in the atmosphere, as shown in Figure 1. In the past, concentrations fluctuated from a low of 180 ppmv and a high of 300 ppmv. However, current levels are approaching the 400-ppmv mark, with a rapidly accelerating rate of increase.
Figure 1: The regular variations in concentration of carbon dioxide over the past 400 thousand years are shown in blue. Fluctuations are mainly due to past glacial cycles. The record of the extreme increase since the Industrial Revolution was found from accumulating data from four different ice cores with varying spacing of samples (Rohde, 2012).
These rising levels of anthropogenic CO2 have a direct impact on seawater pH. As part of the carbon cycle, the ocean naturally absorbs carbon dioxide from the atmosphere and buffers the CO2 changes that occur there (“Ocean Carbon Uptake”). Over the past 200 years oceans have been compensating for the increases in CO2 and have absorbed 525 billion tons of carbon dioxide from the atmosphere, accounting for almost a half of all CO2 released from human activity
(Feely, Sabine and Fabry, 2006). With increasing concentrations in the atmosphere, the current rate of absorption is almost 10 times the natural historic rate. While oceans have helped significantly slow global warming, the greater amount of CO2 is altering the chemical balance of seawater, causing pH to decrease. A decrease in pH means an increase in the acidity of water. Surface ocean pH is already 0.1 unit lower than preindustrial levels and is expected to become another 0.3-0.4 units lower by the end of the century (Orr et al., 2005). While 0.1 unit may seem like a small amount, it is actually a 30% decrease just since the 19th century. The relationship between CO2 and sea surface pH is shown in Figure 2. The past change is already very significant, and according to Ken Caldeira from Carnegie...