A warming planet causes sea-levels to rise for two main reasons. First of all there is increased melting of glaciers and ice sheets, whose melt waters continually add to the total volume of the oceans. Secondly, there is thermal expansion of the oceans: as the water warms up it takes up more space.
Global mean sea level has already risen by around 15cm during the last 100 years, with another 18cm rise predicted due to global warming over the next 30 years. By 2100, if this trend continues, we may see a global rise in sea level of more than 80cm. See the Intergovernmental Panel on Climate Change and the United Nations Framework Convention on Climate Change.
There are more than 50 million people living at less than 80cm above sea level. Though some rich countries may be able to cope with these changes by building expensive sea defences, poor, low lying nations like Bangladesh are likely to be badly hit.
These predictions of sea-level rise are based on what we know about the thermal expansion of water and the response of ice-melt rates to increasing temperature. However, there is the potential for other, much more extreme, increases in sea-level due to disintegration of the Greenland and Antarctic ice sheets. Rather than a steady reduction in these ice sheets over time, there is the potential for rapid disintegration and so much more rapid sea-level rise. For instance, if the West Antarctic ice sheet disintegrated it would raise global sea levels by about 5 metres, while if the Greenland ice sheet collapsed global sea levels could rise by 7 metres.
As well as increased flooding due to sea level rise, climate change in the 21st century is also likely to result in big changes in the amount, timing and location of rainfall. More flash-flooding, as a result of more intense rainfall, is expected in many areas of the world. If the threat from sea-level rise is added to that from more intense rainfall, then by 2080 as many as 2 billion people globally could be at risk of flooding.
Perhaps worse than too much water will be not enough. Though it will rain more heavily in some areas of the world, in other areas rainfall levels are expected to fall drastically. By as early as the year 2025, 5 billion people may be at risk of not having enough water. An increase in the number and intensity of droughts also spells bad news for crop yields – an extra 50 million people could be at risk of starvation due to climate change by the middle of this century.
As the earth’s climate changes, so animal and plant species must either adapt to the new conditions or migrate elsewhere. In many cases, the speed of climate change will be too rapid to allow species to adapt or migrate. As such, a huge number are at risk of extinction due to climate change. Recent predictions suggest that up to a third of all land animal and plant species could be committed to extinction by the middle of this century. In the oceans, increasing temperatures are already resulting in the invasion of many species into cooler waters, while extensive bleaching of coral reefs due to high water temperatures is already being observed. An added threat to marine life is the acidification of the oceans that will occur as carbon dioxide concentrations in the atmosphere increase. Animals with shells made of calcium carbonate, such as shellfish, face a future where the waters they live in may actually start to dissolve them. See this report from the Royal Society.
Many pests and diseases will spread as a result of climate change. An extra 300 million people are expected to be at risk from malaria by 2080, while other diseases, such as Chaga’s Disease, West Nile Virus, Dengue, Bilharzia and even bubonic plague, are expected to become more prevalent.
Migration and Conflict
Some areas of the world, Africa in particular, are likely to suffer some of the most severe impacts of climate change. Impacts like water shortages, crop failures and disease spread are expected to result in 150 million climate change refugees by the year 2050.
With the scarce water supplies, failing crops, and mass migrations, there is a greatly increased risk that local and regional conflicts will arise.
Climate change impacts in the UK
The good news is that higher winter temperatures are expected to reduce the number of cold-related deaths in winter, though the number of heat-related deaths in summer is expected to increase.
By the year 2050, malaria may have become re-established in the south of England. Hotter and sunnier summers are predicted to result in an extra 5,000 cases of skin cancer a year and an extra 10,000 cases of food poisoning.
Severe weather events, such as intense downpours, are likely to become more frequent, with annual flood damage expected to exceed £20 billion by the year 2080.
Sea-level rise will combine with more frequent storm surges to threaten coastal communities – by 2080 storm surges may have become an annual event, today they occur just every 20 years.
Species invasions, both on land and in the sea, will become more common. Spring will come earlier and earlier, while the coming of autumn will recede by several days each decade. Water shortages in the southeast are likely to intensify further.
Climate Change Impacts by region in the UK