Acidification
Dissolving CO2 in seawater increases the hydrogen ion (H+) concentration in the ocean, and thus decreases ocean pH, as follows:
Caldeira and Wickett (2003) placed the rate and magnitude of modern ocean acidification changes in the context of probable historical changes during the last 300 million years.
| Time | pH | pH change relative to pre-industrial |
Source | H+ concentration change relative to pre-industrial |
|---|---|---|---|---|
| Pre-industrial (18th century) | 8.179 | 0.000 | analysed field | 0% |
| Recent past (1990s) | 8.104 | −0.075 | field | + 18.9% |
| Present levels | ~8.069 | −0.11 | field | + 28.8% |
| 2050 (2×CO2 = 560 ppm) | 7.949 | −0.230 | model | + 69.8% |
| 2100 (IS92a) | 7.824 | −0.355 | model | + 126.5% |
Since the industrial revolution began, it is estimated that surface ocean pH has dropped by slightly more than 0.1 units on the logarithmic scale of pH, representing an approximately 29% increase in H+, and it is estimated that it will drop by a further 0.3 to 0.5 pH units (an additional doubling to tripling of today's post-industrial acid concentrations) by 2100 as the oceans absorb more anthropogenic CO2, the impacts being most severe for coral reefs and the Southern Ocean. These changes are predicted to continue rapidly as the oceans take up more anthropogenic CO2 from the atmosphere. The degree of change to ocean chemistry, including ocean pH, will depend on the mitigation and emissions pathways society takes.
Although the largest changes are expected in the future, a report from NOAA scientists found large quantities of water undersaturated in aragonite are already upwelling close to the Pacific continental shelf area of North America. Continental shelves play an important role in marine ecosystems since most marine organisms live or are spawned there, and though the study only dealt with the area from Vancouver to Northern California, the authors suggest that other shelf areas may be experiencing similar effects.
Read more about this topic: Ocean Acidification