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examBoard: Cambridge
examType: IGCSE
lessonTitle: Climate Change and Sea Level Rise
One of the most significant consequences of climate change is sea level rise, which increases flood risks in coastal areas worldwide. As our planet warms, sea levels are rising at an accelerating rate, threatening millions of people living in low-lying coastal regions.
Key Definitions:
As ocean temperatures increase due to global warming, seawater expands. This thermal expansion is responsible for about one-third of observed sea level rise. For every 1°C increase in temperature, sea level rises by approximately 20-30 cm due to thermal expansion alone.
The melting of land ice (glaciers, ice caps and ice sheets) contributes about two-thirds of observed sea level rise. The Greenland and Antarctic ice sheets contain enough water to raise global sea levels by 65 metres if they were to melt completely.
Global sea levels have risen by about 20 cm since 1900. The rate of sea level rise has accelerated in recent decades, from approximately 1.4 mm per year throughout most of the 20th century to 3.6 mm per year from 2006-2015.
Rising sea levels amplify flood risks in coastal areas through several mechanisms:
Higher sea levels mean that storm surges and high tides start from a higher baseline, allowing them to reach further inland.
Events that were once rare (like "100-year floods") become more common, occurring every few years or even annually in some locations.
Rising sea levels can push saltwater into coastal aquifers, raising groundwater tables and reducing soil's ability to absorb rainfall.
Sea level rise is not uniform across the globe. Some regions experience rates of sea level rise up to three times the global average due to factors including:
Bangladesh is one of the most vulnerable countries to sea level rise, with about 80% of the country consisting of floodplains. A 1-metre rise in sea level would submerge about 18% of Bangladesh's land area and directly affect 15 million people. The country already experiences regular flooding, which is becoming more severe as sea levels rise. In coastal areas, saltwater intrusion is reducing agricultural productivity and contaminating drinking water sources.
Rising sea levels have significant environmental consequences for coastal ecosystems:
The human costs of sea level rise and associated flooding are enormous:
London is protected from tidal flooding by the Thames Barrier, which was completed in 1982. The barrier has been closed increasingly frequently in recent years due to high tide events. Originally, planners expected the barrier would need to close 2-3 times per year, but in the 2010s it was closing an average of 6-7 times annually. Without the barrier, sea level rise would put £200 billion of assets and 1.25 million people at risk of flooding in London. The UK Environment Agency is now planning for future sea level rise with its Thames Estuary 2100 Plan, which may require raising the barrier or building a new one further downstream.
These involve building physical structures to protect coastlines:
These work with natural processes rather than against them:
Even with immediate and dramatic reductions in greenhouse gas emissions, sea levels will continue to rise for centuries due to the slow response of oceans and ice sheets. However, the rate of rise can be significantly reduced through mitigation efforts.
Scientists are particularly concerned about "tipping points" in the climate system. For example, the collapse of the West Antarctic Ice Sheet could lead to several metres of sea level rise over centuries. There is evidence that some of these processes may already be underway.
Small island nations like the Maldives, Kiribati and Tuvalu face existential threats from sea level rise. With much of their land just 1-2 metres above sea level, these countries could become uninhabitable within decades. The Republic of Kiribati has purchased land in Fiji as a potential future home for its citizens, while the Maldives has built an artificial island (Hulhumalé) with an elevation of 2 metres above sea level to accommodate population growth and potential displacement from other islands.
Sea level rise due to climate change represents one of the most significant long-term threats to coastal communities worldwide. The combination of rising seas, more intense storms and growing coastal populations creates a perfect storm of increasing flood risk. While adaptation measures can reduce impacts in the short term, long-term solutions require addressing the root cause: reducing greenhouse gas emissions to limit global warming and the resulting sea level rise.
As individuals, we can contribute by reducing our carbon footprints, supporting climate-friendly policies and raising awareness about the links between climate change, sea level rise and flooding. The choices we make today will determine how high seas will rise in the coming centuries and how severely coastal communities will be affected.
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