World under water - Future disasters

If our planet continues to warm up, we could all be in deep trouble. Water expands as it heats, so the ocean would rise and threatens coastlines. There is a danger, too, that the polar ice caps may gradually melt as temperatures increase. Some scientists predict that the combined effect could cause a catastrophic rise in sea levels by the end of 21st century. Without food defences in place, that would put major cities at risk in many heavily populated regions in the world.

Wet outlook

The prospect of coastline cities such as new york sheltering behind sea walls in centuries to come is real. In the last 100+ years sea level has risen by 10-25 cm, and the united nations forecasts that it will rise four times faster in 21st century. Ocean currents will cause much greater rise in some regions, threatening coastlines in future centuries with tides three to five metres higher than present levels - even without the extra hazard of melting polar ice caps.

Disappearing from the map

Some scientists have estimated that sea levels could rise three metres by year 2100. If this happens, dozens of coastal belts, including major cities such as Bangkok, St Petersburg and New Orleans, would face disastrous flooding. Whole regions including southern Florida in the USA, much of the Netherlands and half of Bangladesh would be awash. The area at risk account one third of the world's vital crop growing land.

Mind the gap

Pollution causes more danger than global warming. Chemical called CFCs - used, for example, in aerosols - drifted up in the sky for decades, destroying the ozone layer, the part of Earth's atmosphere that protects us from cancer causing ultraviolet sunlight. The risk was ignored, until a huge whole was detected in the ozone layer over Antarctica in 1987. CFCs are now controlled, but too late to prevent this grave enviromental disaster.

                         Figure is not Thames barrier

Against the tides

The Thames Barrier, which was completed in 1984, protects London from the dangerous high tides that began to flood the city in the 20th century. The main gates, which each weigh 3,700 tonnes, close into a wall as high as a five storey building. The barrier has to be raised 33 times in its first 15 years.