A.3.1. Impacts on natural and human systems from global warming have already been observed (high confidence). Many land and ocean ecosystems and some of the services they provide have already changed due to global warming (high confidence). (Figure SPM.2) {1.4, 3.4, 3.5}
A.3.2. Future climate-related risks depend on the rate, peak and duration of warming. In the aggregate, they are larger if global warming exceeds 1.5°C before returning to that level by 2100 than if global warming gradually stabilizes at 1.5°C, especially if the peak temperature is high (e.g., about 2°C) (high confidence). Some impacts may be long-lasting or irreversible, such as the loss of some ecosystems (high confidence). {3.2, 3.4.4, 3.6.3, Cross-Chapter Box 8 in Chapter 3}
A.3.3. Adaptation and mitigation are already occurring (high confidence). Future climate-related risks would be reduced by the upscaling and acceleration of far-reaching, multilevel and cross-sectoral climate mitigation and by both incremental and transformational adaptation (high confidence). {1.2, 1.3, Table 3.5, 4.2.2, Cross-Chapter Box 9 in Chapter 4, Box 4.2, Box 4.3, Box 4.6, 4.3.1, 4.3.2, 4.3.3, 4.3.4, 4.3.5, 4.4.1, 4.4.4, 4.4.5, 4.5.3}
Fundamental changes (click here) in seawater chemistry are occurring throughout the world's oceans. Since the beginning of the industrial revolution, the release of carbon dioxide (CO2) from humankind's industrial and agricultural activities has increased the amount of CO2 in the atmosphere.
The ocean absorbs about a quarter of the CO2 we release into the atmosphere every year, so as atmospheric CO2 levels increase, so do the levels in the ocean. Initially, many scientists focused on the benefits of the ocean removing this greenhouse gas from the atmosphere. However, decades of ocean observations now show that there is also a downside — the CO2 absorbed by the ocean is changing the chemistry of the seawater, a process called OCEAN ACIDIFICATION....
This is the formula and it may look confusing to some, but, maybe this explanation will help. But, basically what is occurring in the oceans is a REDUCTION of naturally occurring buffer (bi carbonate). The natural pH of the ocean is 8.2. It is now reduced today to 8.1. The problem is the saturation of CO2 into the oceans creating carbonic acid that reacts with it's natural buffer.
Once dissolved in seawater, CO2 reacts with water, H2O, to form carbonic acid, H2CO3:
CO2 + H2O ↔ H2CO3.
Carbonic acid dissolves rapidly to form H+ ions (an acid) and bicarbonate, HCO3-(a base).
Seawater is naturally saturated with another base, carbonate ion (CO3−2) that acts like an antacid to neutralize the H+, forming more bicarbonate. The net reaction looks like this: CO2 + H2O + CO3−2→ 2HCO3-
As carbonate ion gets depleted, seawater becomes undersaturated with respect to two calcium carbonate minerals vital for shell-building, aragonite and calcite. Scientific models suggest that the oceans are becoming undersaturated with respect to aragonite at the poles, where the cold and dense waters most readily absorb atmospheric carbon dioxide. The Southern Ocean is expected to become undersaturated with respect to aragonite by 2050, and the problem could extend into the subarctic Pacific Ocean by 2100 (Orr et al., 2005).
The reduction of the natural ocean buffer may seem silly to many, however, it is not silly to shellfish and their production of their shells.
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This acidification process (click here) decreases the saturation state of aragonite (Ωarag) (right image) and calcite (Ωcal), the two mineral forms of calcium carbonate that most bivalves use to form their shells....
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, CaCO₃. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.
