My Science School

How do we know that the climate has changed?

In more recent times, geologists and paleontologists have been able to make more accurate measurements of the age of ancient rocks. Trees produce a new ‘ring’ every year, and these can be measured and counted. The width of the ring shows how well the tree grew in any year, reflecting climatic conditions at that time. The rings of even partly fossilized trees buried in bogs can be measured, and these measurements provide accurate records of climate changes over the past 750,000 years. By measuring the radioactivity of once living material, scientists can make accurate measurements up to 40,000 years ago. 

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Why did the world’s climate change?

The appearance of living things changed the Earth’s atmosphere, providing the conditions for climate change. The first living things were plant-like creatures. They used the Sun’s energy to change carbon dioxide and water into sugars, which they used for food, and oxygen, which they released into the atmosphere. Some of this oxygen turned into ozone, forming the layer that now protects us from the Sun’s ultraviolet radiation. 

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Poisonous air

The Earth’s original atmosphere was very poisonous. It contained almost no oxygen. It consisted of gases such as hydrogen, helium, methane and ammonia, as well as carbon dioxide. It would have been impossible to breathe in such an atmosphere Lightning and the Sun’s radiation caused chemical reactions in these gases, producing some of the substances characteristic of life, and this may have triggered the development of the first primitive life forms.

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What is an Ice Age?

Ice Ages were periods when large parts of the Earth’s surface were covered by sheets of ice. Each Ice Age has lasted about 100,000 years, with gaps between of up to 20,000 years when the weather was warmer and the ice melted. The last Ice Age ended about 12,000 years ago. Ice ages appear in groups in geological time, each lasting for 20 to 50 million years. The oldest known glacial periods were as long as 2.3 billion years ago. A minor ice age began in the 1500s and lasted for 300 years, during which glaciers were more widespread than at any time for thousands of years.

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Gigantic waterfall!

More than five million years ago, the Mediterranean Sea was a dry basin. Then, movements in the Earth’s crust opened up the Straits of Gibraltar between the land masses of Europe and Africa. The waters of the Atlantic Ocean poured through the gap, flooding the basin. The result was the creation of a gigantic waterfall, at least 800 m high, which let through so much water that the whole of the Mediterranean filled up in few years. 

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What was the Earth like when it was formed?

The Earth had probably existed for around 3,000 million years before the first signs of life appeared. As it cooled after forming from a ball of hot gases, the Earth would have been a relatively smooth sphere. It was covered with shallow seas that contained a mixture of dissolved chemicals, and surrounded by an atmosphere of mixed gases. The atmosphere was full of swirling clouds of vapour, which probably caused huge electrical storms. 

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What is irrigation?

Irrigation is a method of supplying water to crops artificially. It was used in ancient Egypt, and possibly even earlier. Water is pumped out of rivers or wells and fed into channels or canals that carry it for long distances. Modern irrigation systems are usually very extensive.

Elaborate irrigation was used centuries ago in some parts of the world. Native Americans cut long canals along the foot of the Andes to irrigate their crops, which they grew on artificial terraces. Even today, many Asian hillsides are covered with flooded terraces where rice is grown. The terraces are irrigated by complicated canal systems. 

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How do dams affect the environment?

Most dams are built to meet people’s growing demand for water, but sometimes dams cause unforeseen environmental damage. Dams are usually built across valley entrances, creating enormous reservoirs of water. Some are built to provide water for hydroelectric power stations while others control the flow of rivers that are liable to flood. Unfortunately, the best places to build dams are usually in the most picturesque parts of the countryside.

The Aswan High Dam was built to control the flow of the River Nile. However it has prevented the river’s annual flooding, which covered agricultural land with silt.

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What are the effects of deforestation?

Many areas of tropical rainforest are burned to provide farmland, but the effects of this deforestation can be disastrous. After the forest is burned, new fertile ground is exposed. But after one or two years this new land is exhausted. The clearing process is repeated, eventually destroying the forest and its wildlife. The bare ground becomes eroded because there is little vegetation to slow the run-off of rainwater. The water strips away the topsoil, dumping it into rivers. The end-result is useless, infertile land that is prone to flash floods. Also, the smoke from burning forests contributes to global air pollution. 

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Can rivers run backwards?

In the former Soviet Union, the direction of several rivers was diverted or even reversed to provide water for irrigation. Some of the rivers running into the Aral Sea were diverted northwards in a huge water management project to irrigate land north of the region. In some cases the direction of their flow was reversed. The result was that the Aral Sea began to dry up, because no more river water flowed into it. 

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Can we push back the sea?

The action of the waves continually erodes beaches and cliffs, so sea walls are often constructed to protect them. It is very expensive to control the action of the sea in this way. Much of the Netherlands originally lay under the North Sea. For centuries, the Dutch have built enormous dykes (banks) to hold the water back. They have also reclaimed land from the sea, increasing the size of their country by almost one-third.

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Hole in one

In the 1970s, scientists discovered a gap in the protective ozone layer around the Earth. Ozone, a form of oxygen, filters out more than 90 percent of the Sun’s damaging ultraviolet rays. So when a gap in the ozone layer was found over Antarctica, scientists were very concerned. Increased ultraviolet radiation can cause skin cancer. The hole in the ozone layer has been blamed on our use of chemicals called chlorofluorocarbons (CFCs). They were widely used in refrigerators, freezers and aerosol cans. Although the use of CFCs is now heavily restricted, it may take years before the ozone layer repairs itself. 

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What is acid rain?

Rain containing dissolved acids falls to the ground, damaging trees, crops and other wildlife as well as harming water supplies. Acid rain is caused by air pollutants such as nitric and sulphuric acids, which are released by burning coal, oil or petrol. Damage due to acid rain has destroyed huge areas of trees in North America, Europe and parts of Asia, and has had serious effects on forestry. Attempts are being made to limit the damage by removing nitrogen and sulphur from fuels before they are burned, and by reducing emissions from factories. 

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What was the Chernobyl disaster?

In 1986 an explosion in a nuclear power station in the Ukraine was the worst ever nuclear accident. Large amounts of radioactive material were released into the atmosphere, and many people died. Large areas of the Ukraine and neighbouring Belarus were contaminated, and there has been a huge increase in the number of cancers and abnormal births in the region. The radioactive fallout was carried by the wind right across Europe into Sweden and the UK. It is still too dangerous to live in the area around Chernobyl because of the continuing high levels of radioactivity. 

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What is global warming?

Since the late 1800s, the temperature of the Earth’s surface has risen, and it is predicted that this increase will continue. This phenomenon, known as global warming, is thought to result from human activities. By burning wood and fossil fuels such as coal, we have increased the amount of carbon dioxide in the atmosphere by 25 percent. At the same time the average temperature of the world’s surface has increased by about 0.8 degree Celsius. It seems likely that there is a connection between this temperature increase and increased levels of greenhouse gases, such as carbon dioxide. 

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What causes air pollution?

Air pollution is mostly a result of human activities. The exhausts from motor vehicles are one of the main pollutants. They contain greenhouse gases that are thought to contribute to global warming. Exhaust gases also contain substances such as sulphur and nitrogen oxides that can damage the lungs. Recently, vast clouds of choking smoke have appeared over parts of Asia. The smoke comes from the rainforest fires that clear land for farming.

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Can sand dunes move?

Sand dunes can move slowly, causing deserts to spread over more fertile land. Continuous winds blow the sand to form crescent-shaped dunes. Sand from the top of the dune is blown farther away, and it gradually collects to form a new dune.

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How can people live in extreme climates?

Over millions of years, the human body has altered to suit the climate of the regions we inhabit. In general the hotter the region, the darker the skin of its inhabitants. Also, many people from Asia have a fold of skin in their eyelid to protect them from strong sunlight. People living in hot climates do not need a fat layer to keep warm, so they are usually slim. The Inuits of the Arctic, however, are mostly shorter and stockier to help conserve heat. 

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Which are the wettest places on the Earth?

Tropical rainforests are among the wettest places in the world. In general, most rainfall occurs on the sides of hills and mountains. The wettest place of all is Cherrapunji, in Assam, India. It faces the full force of the monsoon winds that sweep in from the Indian Ocean in July. Their warm, damp air rises in the Himalayan foothills, causing torrential rain. Mount Wai-‘ale-‘ale in Hawaii has the wet days each year. It rains on 350 days on average, and the annual rainfall is the highest recorded anywhere.

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What is permafrost?

Permafrost is a layer of ice and frozen soil that never thaws. It lies beneath nearly one-quarter of the Earth’s surface, throughout Alaska, Canada and Russia. Sometimes the soil in these places is frozen to a depth of up to 1,500 m. The surface layers may melt enough in summer for plants to grow, but the soil beneath is permanently frozen.

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Are there places where nothing can live?

Hot volcanic lava is probably the only place on the Earth’s surface where there is no life at all. Living things have evolved to survive in the harshest environments. Tiny bacteria can be found everywhere on the Earth, even buried in thick ice at the poles or in the very deepest parts of the ocean. 

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Where are the most extreme temperatures found?

Libya and the Antarctic have recorded the most extreme temperatures. The hottest shade temperature was in Libya in 1922, when the temperature in the Sahara desert reached 58 °C. Temperatures nearly as high as this were recorded in Death Valley in the USA in 1913. The coldest ever recorded temperature was in Antarctica in 1983, when Russian scientists measured a temperature low of - 89.2°C.

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The desert process

Deserts were once green and fertile areas, until a climate change altered them permanently. Just a small reduction in rainfall causes plants to die off. Without plant roots to bind and nourish the soil, the land gradually becomes barren. Soon the animals move away, and only desert remains. Very few deserts are completely barren, and plants and animals have evolved to live in the driest conditions, conserving their body water so they do not need to rely on rainfall.

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Are there cold deserts?

Antarctica is the biggest cold desert in the world. All of its water is locked up in ice and snow, so nothing can grow. The Gobi desert in Mongolia and western China is also very cold in the winter, when temperatures drop below freezing. However, it is hot in the summer.

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What is a mirage?

Mirages form in hot deserts, where the air is so hot it bends and distorts light rays. The shimmering images that a mirage produces have often tricked travellers in deserts. People think that they can see a town or oasis on the horizon, but in reality there is none. 

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Where is the world’s driest place?

The world’s driest place is the Atacama Desert in Chile. It is a narrow strip between the Andes and the Pacific, where the first rain for 400 years fell in 1971. Like other hot deserts, the Atacama lies in a region where air pressure is constantly high, with little air movement or cloud. Rainfall is very low in other deserts. Near Cairo, Egypt, annual rainfall averages about 28 mm each year, while in Bahrain, on the edge of the Arabian Desert, there is as much as 81 mm of rainfall. The rain may come in a single heavy storm, and some years there is no rainfall at all. 

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How much of the world is covered by desert?

About one-third of the world’s land surface is covered by desert. Desserts are found wherever there is too little water to allow much plant life to grow. This lack of vegetation leaves large areas of soil exposed. The largest desert in the world is the Sahara in Africa. It has an area of about 9 million sq km. 

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