Oceans

How much excess heat from greenhouse gases do oceans absorb?

~90% of excess heat, reducing atmospheric warming but driving marine heatwaves and ice melt.

How much CO₂ do oceans absorb from human emissions?

~30%, lowering ocean pH and causing acidification.

How much has the ocean warmed compared to land since 1901?

Oceans: ~0.77°C; Land: ~1.43°C (greater heat capacity of water).

How much has global sea level risen in the last century?

~10–25 cm.

Projected global sea level rise by 2100?

~50 cm.

How many people are threatened by sea-level rise?

~680 million in low-lying areas; ~2 billion in coastal megacities.

Why does ocean warming reduce oxygen levels?

Warmer water holds less dissolved oxygen, expanding dead zones.

Name major global dead zone regions.

Gulf of Mexico, Baltic Sea, Arabian Sea, parts of the Pacific Ocean.

What causes eutrophication?

Nitrogen and phosphorus runoff from agriculture, industry, and urban areas.

Why are algal blooms an example of global + local interaction?

Local nutrient pollution amplified by global climate warming.

What percentage of Earth’s surface is ocean?

~75%.

What percentage of Earth’s water is in oceans?

~97%.

What proportion of global trade is transported by sea?

~90%.

How much are oceans worth economically each year?

~$7 trillion in ecosystem services and economic activity.

What proportion of the global population lives near coasts?

~50% within 100 km of the coast.

What are the health impacts of polluted seas?

~250 million illness cases per year; ~$1.6 billion cost.

Impacts of contaminated shellfish consumption?

~2.5 million hepatitis cases annually; ~$10 billion cost.

How many species are moved daily by ballast water?

~3,000 species per day.

How much fish is captured globally each year?

~90 million tonnes.

What percentage of fish stocks are overfished?

~25%.

What proportion of fisheries lie within EEZs?

~90%.

How important is offshore oil and gas globally?

Offshore oil ≈ 30% of global oil; offshore gas ≈ 50% of global gas.

What is the significance of methane hydrates?

Store ~2× more carbon than all fossil fuels combined.

Key facts of the Deepwater Horizon spill (2010)?

4.9 million barrels spilled; 87 days; ~180,000 km² affected.

Environmental impacts of Deepwater Horizon?

~800,000 birds killed; ~1,400 marine mammals stranded.

Economic impacts of Deepwater Horizon?

⅓ Gulf waters closed; 8,000–12,000 jobs lost; $20bn compensation fund.

How many oil spills have occurred in the Niger Delta since the 1970s?

7,000 spills.

Why is the Niger Delta an example of environmental injustice?

Resource extraction benefits global markets while local ecosystems and livelihoods collapse.

What temperature range do ocean surface waters experience?

~35°C at equator to ~-2°C at poles.

Where do hydrothermal vents form?

Divergent plate boundaries (e.g. Mid-Atlantic Ridge).

Why are upwelling zones important for fisheries?

Bring nutrient-rich water to the surface, boosting productivity (e.g. Peru–Chile).

What is UNCLOS (1982)?

Global legal framework for oceans; defines EEZs to 200 nautical miles.

How much of the ocean is high seas under UNCLOS?

~64% — weak enforcement.

Why are EEZs important?

Cover ~36% of oceans but ~90% of known marine resources.

What is MARPOL and why is it effective?

Shipping pollution treaty; >99% of shipping covered; oil spills reduced ~90%.

How much of the ocean is protected by MPAs?

~8% designated; <3% strongly protected.

Why are many MPAs criticised?

30–50% are “paper parks” with weak enforcement.

What is the Basel Convention?

Controls hazardous waste trade; often shifts pollution rather than reducing it.

How much plastic enters oceans each year?

~11 million tonnes (projected to triple by 2040).

Size and composition of the Great Pacific Garbage Patch?

~1.6 million km²; 75–86% ghost fishing gear.

What is CCAMLR?

Antarctic marine governance body using ecosystem-based management.

Krill TAC under CCAMLR?

620,000 tonnes/year (~11% of estimated sustainable yield).

How much has krill biomass declined since the 1970s?

~80% decline.

Why is Rockall geopolitically important?

Extends EEZ claims over fisheries and oil/gas resources.

Why is tidal energy considered reliable?

100% predictable decades in advance.

Key limitation of tidal and wave energy?

High upfront costs and limited suitable locations; <1% of global electricity.