Climate Change & Ocean Acidification (DP IB Environmental Systems & Societies (ESS))

Revision Note

Written by: Alistair Marjot

Reviewed by: Bridgette Barrett

Climate change refers to significant changes in global temperatures and weather patterns over time
- Mostly driven by human activities such as burning fossil fuels, deforestation and industrial processes
- Leads to global warming, which is an increase in Earth's average surface temperature

Ocean acidification is the ongoing decrease in the pH of Earth's oceans
- Caused by absorption of excess carbon dioxide (CO₂) from the atmosphere
- When CO₂ dissolves in seawater, it forms carbonic acid, which lowers the pH

Temperature rise:
- Warmer waters can alter habitat ranges for marine species
  - For example, many fish populations are migrating to cooler waters, impacting local fishing industries
Melting ice caps:
- Polar ice is important for the survival of many species
  - For example, the loss of important ice habitats will affect polar bears and seals that need them for hunting, avoiding predators and raising offspring
  - Walruses are increasingly forced to rest on land, leading to overcrowding and increased mortality
- Leads to sea level rise, threatening coastal ecosystems
  - For example, rising sea levels are threatening the coastal mangrove forests in Bangladesh, which serve as crucial habitats for many species and protect the coastline from erosion
Hurricane damage:
- Increased intensity and frequency of hurricanes is damaging coral reefs (e.g. in the Caribbean)
  - For example, hurricane Irma in 2017 caused widespread coral destruction, particularly affecting the coral reefs around the Florida Keys and the Virgin Islands

Coral bleaching:
- Warmer temperatures and acidification cause coral to expel the algae that live in their tissues
- This causes the coral to turn white (known as bleaching)
- This often leads to coral death if the stressful conditions persist
  - For example, the Great Barrier Reef is currently experiencing massive coral bleaching events
Shellfish vulnerability:
- Acidic waters weaken calcium carbonate shells of marine organisms like oysters, clams, and sea urchins
- This makes them more vulnerable to predation, disease and environmental stress,
- This can lead to population declines and disruption of marine food webs
  - For example, oyster populations in the Pacific Northwest (USA) are in decline partly due to ocean acidification
  - Oyster farms here are struggling with reduced harvests due to shell degradation

The Great Barrier Reef

Location and importance

Stress factors

Coral bleaching events:
- Repeated bleaching events have caused significant damage
- In 2016 and 2017, back-to-back bleaching events affected two-thirds of the reef
Rising sea temperatures:
- Even very small increases in temperature can trigger bleaching events
Ocean acidification:
- This is weakening coral structures, making them more susceptible to erosion and breakage

Wider impacts on the ecosystem

Biodiversity loss:
- Coral reefs support many marine species
- Coral bleaching leads to the loss of habitat and food sources for these organisms, resulting in decreased biodiversity
Fishing industry:
- The Great Barrier Reef supports commercial and recreational fishing industries
- Coral bleaching reduces fish populations, affecting the livelihoods of local fishermen and the economy
Tourism:
- The reef is a major tourist attraction, bringing in millions of visitors annually
- Bleached and dying corals reduce the aesthetic and ecological value of the reef
- This leads to a drop in tourism revenue
  - For example, snorkelling and diving tours experience decreased interest as the vibrant coral ecosystems become bleached and lifeless
Coastal protection:
- Coral reefs act as natural barriers, protecting coastlines from storm surges and erosion
- Damaged and weakened reefs are less effective at buffering waves, leading to increased vulnerability of coastal populations
  - For example, communities along the Queensland coast are facing higher risks of flooding and property damage due to weakened reef structures
Marine food web disruption:
- Coral reefs are integral to marine food webs
- Bleaching disrupts these webs by removing key species and altering predator-prey relationships

Last updated: 13 June 2024

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