Why is sea water essential

Climate FAQ 3.3 | Ocean acidification

Both anthropogenic climate change and anthropogenic ocean acidification are caused by increasing carbon dioxide concentrations in the atmosphere. Increasing levels of carbon dioxide (CO2) and other greenhouse gases together indirectly change the climate system by retaining heat that is reflected from the earth's surface. Anthropogenic ocean acidification is a direct consequence of increasing CO2 concentrations, as seawater currently absorbs around 30% of anthropogenic CO2 from the atmosphere.

Ocean acidification refers to a decrease in pH over a longer period of time, usually decades or longer, primarily caused by the uptake of CO2 from the atmosphere. pH is a dimensionless measure of acidity. Ocean acidification describes the direction of the pH change rather than the end point. This means that although the pH of the sea is decreasing, it is not expected to become acidic (pH <7). Ocean acidification can also be caused by other chemical additions or withdrawals that are natural (e.g. increased volcanic activity, methane hydrate release, long-term changes in net respiration) or anthropogenic (e.g. release of nitrogen and sulfur compounds into the The atmosphere). Anthropogenic ocean acidification refers to that portion of the pH decrease caused by human activity.

Since around 1750, the release of CO2 from industry and agriculture has increased mean global atmospheric CO2 concentrations from 278 to 390.5 ppm in 2011. Atmospheric CO2 concentration on earth is thus higher today than it has ever been in at least the last 800,000 years, and it is expected to continue to rise due to our reliance on fossil fuels for energy. To date, the oceans have absorbed about 155 ± 30 PgC from the atmosphere, which is roughly a quarter of the total amount of CO2 (555 ± 85 PgC) emitted by human activities since pre-industrial times. This natural absorption process has significantly reduced the level of greenhouse gases in the atmosphere and reduced some of the effects of global warming. However, the uptake of CO2 by the ocean has a significant impact on the chemistry of seawater. The mean pH value of sea surface water has already decreased by around 0.1 units, from around 8.2 to 8.1 since the beginning of the Industrial Revolution. Estimates of projected future atmospheric and oceanic CO2 concentrations suggest that by the end of this century the mean sea surface pH could be 0.2-0.4 lower than it is today. The pH scale is logarithmic, so a change of one unit corresponds to a ten-fold change in the hydrogen ion concentration.

When atmospheric CO2 is exchanged at the interface between the air and the sea, it reacts with the seawater in a series of four chemical reactions, increasing the concentration of carbon compounds - dissolved carbon dioxide (CO2 (aq)), carbonic acid (H2CO3) and bicarbonate (HCO3- ) - increases: