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Could we control our climate?
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4.1 Ocean acidification

One of the predicted Earth system changes is further ocean acidification. This may have different effects on different species. Those that photosynthesise – algae and seagrasses – may benefit from higher CO2, just like plants on land would. However, many species that are important to humans are thought to be vulnerable, especially for the higher forcing scenarios RCP6 and RCP8.5.

Figure 10 shows that negative effects from ocean acidification are predicted for a large number of important marine species, particularly molluscs and warm-water (reef-building) corals.

This is contains a colour coded global map showing changes in ocean pH for the RCP8.5 scenarios. It shows that there is a reduction in pH (acidification) over most of the world's oceans. The map also indicates: Regions of mollusc and crustacean fisheries in many coastal regions (particularly North America, South America, India and East Asia. Regions of cold water corals, particularly in the fringes and middle of the north Atlantic and between Australia and New Zealand Regions of warm-water corals, including the oceans of Central America, and in an equatorial band across most of the Pacific and around the islands of south east Asia. Many of the highlighted regions are found in regions of large decreases of pH. The figure also includes bar charts indicating the numbers of species in various groups, in a range of RCP scenarios (RCP4.5, RCP 6.0 and RCP 8.5, in order of increasing magnitude) Molluscs - negative effects on about 50% of species for all scenarios. Crustaceans - no effects or positive effects for the lightest scenario, increasing up to negative effects for 20% of species in the most sever scenarios. Cold water Corals - increasing number of species experiencing negative effects as the scenarios get worse. Warm water Corals - between 25 and 50 % of species affected, rising as the scenarios get worse.
Figure 10 IPCC (2014) predictions for ocean acidification for RCP8.5, along with the estimated sensitivity of molluscs, crustaceans and corals – vulnerable animal phyla with socio-economic relevance (e.g. for coastal protection and fisheries) – for different RCPs (adapted from IPCC, 2014).
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This is contains a colour coded global map showing changes in ocean pH for the RCP8.5 scenarios. It shows that there is a reduction in pH (acidification) over most of the world's oceans. The map also indicates: Regions of mollusc and crustacean fisheries in many coastal regions (particularly North America, South America, India and East Asia. Regions of cold water corals, particularly in the fringes and middle of the north Atlantic and between Australia and New Zealand Regions of warm-water corals, including the oceans of Central America, and in an equatorial band across most of the Pacific and around the islands of south east Asia. Many of the highlighted regions are found in regions of large decreases of pH.

The figure also includes bar charts indicating the numbers of species in various groups, in a range of RCP scenarios (RCP4.5, RCP 6.0 and RCP 8.5, in order of increasing magnitude) Molluscs - negative effects on about 50% of species for all scenarios. Crustaceans - no effects or positive effects for the lightest scenario, increasing up to negative effects for 20% of species in the most sever scenarios. Cold water Corals - increasing number of species experiencing negative effects as the scenarios get worse. Warm water Corals - between 25 and 50 % of species affected, rising as the scenarios get worse.

Figure 10 IPCC (2014) predictions for ocean acidification for RCP8.5, along with the estimated sensitivity of molluscs, crustaceans and ...

  • Which species are in regions affected by the largest predicted pH changes?

  • The largest pH changes are in the Arctic (decreases: dark blue), which has molluscs and crustaceans (yellow) and cold-water corals (red).

  • Which of those three species (molluscs, crustaceans and cold-water corals) are estimated to be more affected by pH?

  • Warm-water corals and molluscs: these have the largest estimates of negative effects (dark bars).

Why is this important? You will see later that some types of geoengineering would address ocean acidification because they tackle the root cause of climate change – greenhouse gas emissions – but others would not.