pratclif.comCarbon dioxide (CO2) is one of the most important gases in the atmosphere, affecting the radiative heat balance of the earth as well as the calcium carbonate (CaCO3) equilibrium of the oceans. For 650,000 y (650 ky) prior to the Industrial Revolution, atmospheric CO2 concentrations remained between 180 to 300 parts per million by volume (ppmv) (Petit et al., 1999; Augustin et al., 2004; Siegenthaler et al., 2005). Increased fossil fuel burning associated with industrialization, cement production, and land use changes associated with agricultural activities are causing atmospheric CO2 concentrations to rise, and at increasing rates (rates of increase have risen from 0.25% y-1 in the 1960s to 0.75% y-1 in the last five years). The current atmospheric CO2 concentration is about 380 ppmv and is expected to continue to rise by about 1% y-1 over the next few decades (Houghton, 2001) (Figure 1–1). The rate of current and projected CO2 increase is about 100x faster than has occurred over the past 650,000 years and the rising atmospheric CO2 levels are irreversible on human timescales (Royal Society, 2005).
Over the two decades of the 1980s and 1990s only about half of the CO2 released by human activity has remained in the atmosphere, with the oceans having taken up about 30% and the terrestrial biosphere 20% (Sabine et al., 2004). Similar partitioning of anthropogenic CO2 is expected to continue with the result that the partial pressure of CO2 (pCO2) dissolved in the surface ocean is likely to double its pre-industrial value within the next 50 years. Over the next millennium, the ocean will absorb about 90% of the anthropogenic CO2 released to the atmosphere (Archer et al., 1998).
Increasing the amount of CO2 dissolved in the ocean lowers the pH, and decreases the availability of carbonate (CO2- 3 ) ions and lowers the saturation state of the major shell-forming carbonate minerals (Box 1). Tripling the pre-industrial atmospheric CO2 concentration will cause a reduction in surface ocean pH that is almost three times greater than that experienced during transitions from glacial to interglacial periods. This is often termed “ocean acidification” because it describes the process of decreasing pH. Current projections of ocean acidification suggest that the pH of surface ocean waters will continue to decline. However, the term can also lead to confusion when it is wrongly assumed that the oceans will become acidic, when in reality, ocean pH is never expected to fall below 7.0; i.e., the oceans are becoming less basic, but not acidic. Such a phenomenon could only occur in the unlikely event that CO2 emissions reach more than 10,000 Pg C (Caldeira and Wickett, 2005). In this report, we use the term “ocean acidification” to conform with current terminology, with the recognition that it refers to the process rather than an end state.
See here two major scientific studies on ocean uptake of atmospheric CO2.
Mis à jour le 11/10/2016 pratclif.com