# Unit 9: Global Change: 4.58: ocean warming and acidification
Two main ideas:
1. Global warming is causing ocean water to expand, rising sea levels
2. Increased CO2 in the atmosphere is changing the pH of the oceans (ocean acidification)
- Some lakes (confined, smaller bodies of water) have increased by 2°C or more
- Oceans has warmed by 1.5-2°C
- 2.7°C in the top layers (!)
- Kyoto protocol: 5.2% decrease in greenhouse gases by 2012
- Paris climate Accord: 2°C max temp increase
Result:
- fish migration, northwards
- coral bleaching: mutualistic algae ([zooxanthellae](https://en.wikipedia.org/wiki/Zooxanthellae)) dies
- corals are sensitive to pH, temp, sedimentation, pollution, disease and salinity (few corals on windward shores of Hawaii due to freshwater runoff)
- some genetic researchers are trying to create heat resistant corals (CRISPR) and other variants of zoozanthellae (A-C)
Ocean acidification:
## CO2 + H2O <--> H2CO3 <--> HCO3- + H+
## H2CO3 is carbonic acid
H+ joins with water to become H3O+ known as the hydronium ion (basis for low pH)
Screen Shot 2023-04-08 at 4.02.29 PM.png
Important:
As pH decreases, CaCO3 in corals dissolves (AP exam question last year) and creatures have a harder time absorbing calcium carbonate
Coral Bleaching:
Screenshot 2025-04-25 at 4.59.45 AM.png
Here’s how to read this:
The top formula is what you know already:
CO2 + H2O <-> H2CO3<-> H+ + HCO3-
The next bit is more complex:
Since there is lots of H+ in the ocean with acidification, it pulls CO3-- out of coral:
Follow coral from the left:
CaCO3—>Ca++ + CO3-
CO3-- + H+ —> HCO3-
This second part is what you may be asked about on the AP exam...