🌊 Effects of Climate Change
Climate change produces effects at every scale — from the melting of polar ice to changes in crop yields in individual farming communities. In the exam, you will gain higher marks by organising effects under clear headings and by connecting physical changes to their human consequences. The strongest answers recognise that physical and human effects are deeply linked: a rise in sea level is a physical change, but it becomes a human catastrophe when millions of people lose their homes and livelihoods.
Physical Effects
Sea level rise — a slow-moving catastrophe: Global mean sea level has risen 21–24 cm since 1880 and is currently rising at 3.7 mm per year. Projections suggest a further 0.3–1 m by 2100 under current trajectories, with higher estimates possible if large ice sheet instabilities are triggered. Even modest rises threaten enormous populations: Bangladesh has approximately 17 million people living within 1 metre of sea level; the Maldives has an average land elevation of just 1.5 m above sea level; the Pacific island nation of Tuvalu is purchasing land in Fiji in anticipation of becoming uninhabitable. Coastal cities including Miami, Jakarta, Mumbai and Shanghai face growing flood risk.
More intense storms: Tropical storms (hurricanes and typhoons) draw their energy from warm ocean water. As sea surface temperatures rise, the maximum potential intensity of tropical storms increases. While the total number of tropical storms may not change significantly, the proportion reaching the highest categories (4 and 5) is projected to increase. The 2017 Atlantic hurricane season — which included Harvey, Irma and Maria — caused approximately $300 billion in damage, part of a trend of rising economic losses from extreme weather.
Drought and water stress: Climate change is projected to intensify the global water cycle — wet areas getting wetter, dry areas getting drier. The Mediterranean region (southern Europe, North Africa, Middle East) is one of the most drought-affected areas, with rainfall declining and temperatures rising significantly faster than the global average. California experienced its driest three-year period on record (2020–2022) before catastrophic flooding in 2023 — demonstrating how climate change increases the swings between extremes as well as the averages. The Sahel in sub-Saharan Africa faces increasingly severe and prolonged droughts, threatening food and water security for hundreds of millions of people.
Flooding and extreme rainfall: While droughts increase in some regions, other areas face greater flood risk as a warmer atmosphere holds more water vapour and produces heavier rainfall events when it does rain. The UK experienced unprecedented flooding in 2020 (Storm Dennis) and 2021 (flooding in London's underground). Germany and Belgium experienced catastrophic flash flooding in July 2021, killing over 200 people in events that scientists attributed partly to climate change. Thawing permafrost in Arctic regions releases methane (a more potent greenhouse gas than CO₂), creating a positive feedback loop that accelerates warming.
Ecosystem disruption: Coral bleaching has been described above. Polar bears require sea ice to hunt seals — declining Arctic sea ice is reducing their habitat. Phenological mismatches are emerging: some species are responding to warming by advancing their seasonal behaviour (e.g. plants flowering earlier), while other species in the same ecosystem are not, disrupting food webs. Species are migrating poleward and to higher altitudes as temperatures rise — but not all species can do so, and many face extinction.
Human and Economic Effects
Food security: Crop yields are projected to decline in many tropical and subtropical regions as temperatures rise beyond optimal growing conditions. The IPCC projects that climate change could reduce crop yields for staple foods (wheat, rice, maize) by 2–6% per decade in a 2°C warming scenario. At the same time, some higher-latitude regions (Canada, Russia, Scandinavia) may see increased yields as temperatures warm. The net effect is an increase in global food insecurity, concentrated in the countries that are already most vulnerable.
Human migration: The World Bank projects that climate change could force 216 million people to migrate internally within their own countries by 2050 in a business-as-usual scenario, as water stress, crop failures, sea level rise and coastal flooding make their home regions unliveable. This represents one of the largest forced migration events in human history — with profound implications for geopolitical stability, urban infrastructure and international relations.
Health: Rising temperatures increase heat stress mortality directly; global heat-related deaths have increased significantly in the 21st century. Warmer temperatures are also expanding the range of vector-borne diseases: malaria (carried by Anopheles mosquitoes) is spreading to higher altitudes in East Africa and South Asia as temperatures permit mosquito survival. Dengue fever is expanding its range significantly. Air quality deteriorates in heat waves as ground-level ozone forms more readily.
Economic damage: Global insured losses from natural disasters reached approximately $100 billion in 2023 — and uninsured losses were considerably higher. Developing countries tend to bear a disproportionate share of climate-related economic losses relative to their GDP. The economic cost of inaction on climate change is projected to significantly exceed the cost of mitigation: the Stern Review (2006) estimated that unmitigated climate change could reduce global GDP by 5–20%, while the cost of stabilising emissions would be approximately 1% of GDP per year.
