Global warming risks: low-lying coasts, mega-deltas and the Sahel

Low-lying countries: the Maldives

• About 80% of the Maldives' islands are less than one metre above sea level (World Bank).
• Sea level around the islands could rise 0.5 to 0.9 m by 2100.
• Tourism and fishing are the two main industries, both exposed to coastal flooding and coral reef damage.
• Under high emissions, coastal flooding could cut GDP by up to 11% by 2050; smart adaptation, economic reforms and global cooperation could cut these losses in half (World Bank, May 2025).
• Options: coral reef restoration, mangroves, engineered coastal protection, island-specific plans.

Asian mega-deltas and coastal cities

• The IPCC identified the Ganges-Brahmaputra (Bangladesh) and Mekong (Vietnam), with the Nile, as mega-deltas where more than 1 million people each will be directly affected by 2050. About 75% of the population affected by 2050 lives in Asian megadeltas and deltas (IPCC AR4).
• Deltas are already sinking: natural compaction, groundwater extraction and sediment trapped behind dams, so relative sea level rises faster than the global average.
• Many contain megacities with dense populations and valuable infrastructure.
• Economic vulnerability of coastal cities depends on wealth: richer cities can invest in defences; the June 2025 examiners rewarded answers that linked wealth to investment, not just physical exposure.

Shifting climate belts: the Sahel

• In Africa 95% of cropland is rain-fed (IPCC AR6 Chapter 9), so farmers depend on the timing and amount of rainfall.
• Climate change has reduced African agricultural productivity growth by 34% since 1961, more than any other region; multi-year droughts have become more frequent in West Africa.
• Above 2 C of global warming, West African maize yields could fall by 20 to 40%.
• Low-income subsistence farmers lack irrigation, savings and insurance, so a failed rainy season quickly means food insecurity and migration.

Worked example

Suggest why the impacts of global warming will be uneven between the Maldives and the Netherlands, both low-lying.

1. Physical exposure is similar: much land is close to sea level.
2. Economic vulnerability differs: the Netherlands is wealthy and can fund defences, while the Maldives is a small economy dependent on tourism and fishing.
3. So the same sea-level rise threatens the survival of the Maldives far more.

Answer: Similar physical exposure, very different capacity to pay for adaptation.

Check yourself

1. Coastal flooding could cut Maldives GDP by up to 11% by 2050, and the World Bank says adaptation, reforms and cooperation could cut those losses in half. What would the maximum loss be then, as a percentage of GDP?
   Show answer

   5.5 %. 11 / 2 = 5.5% of GDP.

2. Practice question: a Sahel farm yields 1.5 tonnes of maize per hectare. What would it yield after the upper IPCC estimate of a 40% fall?
   Show answer

   0.9 tonnes per hectare. 1.5 x 0.6 = 0.9 tonnes per hectare.

3. What share of Africa's cropland is rain-fed, according to IPCC AR6?
   • 95%
   • 50%
   • 25%
   • 5%
   Show answer

   95%. IPCC AR6 Chapter 9: 95% of cropland is rain-fed.

4. Which pair are Asian mega-deltas identified by the IPCC as highly vulnerable?
   • Nile and Mississippi
   • Rhine and Thames
   • Amazon and Congo
   • Ganges-Brahmaputra and Mekong
   Show answer

   Ganges-Brahmaputra and Mekong. Both have over 1 million people directly affected by 2050.

5. Why is relative sea level rising faster than the global average in many deltas?
   • Deltas are on divergent plate boundaries
   • The land is sinking from compaction, groundwater extraction and sediment trapped behind dams
   • The tides are larger in deltas
   • Rivers add water to the ocean
   Show answer

   The land is sinking from compaction, groundwater extraction and sediment trapped behind dams. Subsidence adds to sea-level rise.

6. Which statement best describes the economic vulnerability of a coastal city to sea-level rise?
   • Its height in metres over sea level
   • The number of beaches it has
   • Its distance from a plate boundary
   • Its ability to pay for defences and recover depends on its wealth and the value of assets exposed
   Show answer

   Its ability to pay for defences and recover depends on its wealth and the value of assets exposed. Economic vulnerability is about money and assets, not only height.

7. Explain why low-income farmers in the Sahel are especially vulnerable to shifts in climate belts.
   Show answer

   They depend on rain-fed crops and cannot afford irrigation, so when the rains fail or shift their crops fail, causing food shortages and loss of income.. Dependence on rain, no money for irrigation, so crop failure and hunger.

Practise with instant feedback Print this lesson

Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification (Issue 3, September 2025)
• World Bank blog: Rising to the climate challenge, how the Maldives can thrive in a warming world (20 May 2025)
• IPCC AR4 Working Group II, Cross-chapter case study C3: Megadeltas
• IPCC AR6 Working Group II, Chapter 9: Africa (2022)
• Pearson principal examiner report, WGE01 Global Challenges, June 2025

Last updated 8 November 2026. Spotted a mistake? Tell us.