Climate Change (5-) (1)
CHAPTER FIVE
The causes of climate change
Carbon sinks and carbon in the atmosphere
On Earth, there is a carbon cycle. Carbon dioxide is a very important gas for life on Earth. Plants need it to live. They take in carbon dioxide, use the carbon to grow and then put oxygen back into the atmosphere. People and animals then take in this oxygen, use it to live and put carbon dioxide back into the atmosphere. When plants and animals die, the carbon in their bodies can go back into the atmosphere as carbon dioxide, or it can go into the ground in their bodies. The carbon dioxide on Earth moves between the land and the atmosphere, and between the ocean and the atmosphere, too.
A carbon sink is something that takes in carbon and holds it for a long time. The land and forests on Earth are huge carbon sinks because they take in a lot of carbon dioxide. This is called the land sink. The oceans also take in a lot of carbon dioxide, so they are huge carbon sinks, too. This is called the ocean sink. Together, the land sink and ocean sink take in and hold over half the carbon dioxide that people put into the atmosphere. The other half stays in the atmosphere because there is nowhere for it to go and no way for it to get out.
The carbon sinks on Earth are very important.
They stop the Earth from getting even warmer.
Every year, people put about 40 billion tonnes of carbon dioxide into the Earth's atmosphere. Most of this carbon dioxide comes from burning fossil fuels and from factories, but some of it comes from deforestation and from changing the way, we use the land.
Over the years since the last Ice Age, the Earth has become about 4C to 5C warmer. This warming was because of the natural changes in the way the Earth moves around the Sun. This change in temperature has had a huge effect on the Earth, its climate, and the plants and animals that live here.
If we do not stop putting so much carbon dioxide into the atmosphere, the Earth's temperature may increase by another 4C to 5C by the end of the 21st century. This would cause huge problems for all the living things on the Earth.
The energy we use now and in the future
Across the world, people use twenty times more energy today than they did in 1850. In this time, there has also been a change in the energy we use. In the past, we burned wood and used energy from the wind and from the water in rivers. Today, we burn a lot more fossil fuels than we did in the past. As we built more and more factories, we started to use more and more fossil fuels. We also started to drive cars and travel in planes, and this burns fossil fuels, too.
Today, 80 percent of the energy we use comes from fossil fuels. Energy from other things, including wood and water, is just 20 percent of the energy we use. Right now, energy from the Sun and from the wind is just 3 percent of the energy we use, but this is growing quickly. The energy we get from the Sun and wind is much better for the Earth than fossil fuels because it is clean and does not put any greenhouse gases into the atmosphere. Countries need to work hard to increase the amount of clean energy they use.
For countries around the world, getting clean energy to people at a low price is one of the biggest problems of the 21st century. As the number of people in the world grows, the amount of energy we need also grows, and this is becoming a bigger and bigger problem for everyone.
Around the world, more than 1 billion people live without electricity for heat and light in their homes. Most of these people live in Africa and Asia.
Over 3 billion people still use wood in their homes for cooking, and this can make the air inside their homes very dirty and dangerous. It can have a very bad effect on their health, and millions of people die every year because of dirty air inside their homes. Outside, fossil fuels also have a bad effect on people's health. Burning fossil fuels in factories, and in cars and buses, causes millions of people to die every year from dirty air.
Clean energy from the Sun, wind and water is the best way to give people the energy they need without having the damaging effects on people's health and on the Earth's climate.
Cutting down forests and damaging soils
Forests are one of the biggest carbon sinks on Earth. Across the world, forests take in carbon dioxide and hold it in their trees, plants and the soil under them. When we cut down trees, most of that carbon dioxide goes back into the atmosphere.
For thousands of years, people have cut down forests to use the land for farming. This deforestation put a lot of carbon dioxide into the atmosphere and also caused some animals to become extinct. Tarpans were wild horses and aurochs were wild cows, and both of these animals became extinct when people cut down forests in Europe, Asia and North Africa.
In the last century, the deforestation of rainforests in some parts of the world has become a big problem. Some of these rainforests are on soils that hold a huge amount of carbon. These soils have taken in the carbon slowly over thousands of years.
When people cut down the trees in these rainforests, they damage the soil under the trees, and this puts the carbon dioxide back into the atmosphere. Farming can also damage soils and put even more carbon dioxide into the atmosphere.
Today, people are still cutting down forests, often to build huge farms. Over the last 150 years, 25 percent of the carbon dioxide put into the atmosphere by people is because of deforestation.
Cutting down forests has a bad effect on the water cycle, too, and this can make droughts worse in some parts of the world. Deforestation also puts many animals and plants in danger because it takes away their habitats. It may cause many animals to become extinct in the future.
Past and present changes in carbon dioxide
The carbon dioxide levels in the atmosphere today are much higher than at any time in the last 800,000 years. We know this because many scientists work in Antarctica and study the ice there. Scientists take ice cores from the Antarctic ice and use them to find out about the Earth's climate in the past. These ice cores show that the changes in the last century are not part of Earth's natural cycles.
The ice in Antarctica has built up over hundreds of thousands of years. Over this time, snow fell and made layers that built up to make the thick ice that we see in Antarctica today. Every time the snow fell, small amounts of air also got inside the ice and could not get out. Scientists can take ice cores from more than 3,000 metres down to find air from hundreds of thousands of years ago. By studying this air, they can find out about the atmosphere in the past.
We can also study the soil at the bottom of the ocean to find out about the Earth's atmosphere a very long time ago.
All of these studies show that carbon dioxide is going into the atmosphere more quickly now than at any time in the past 50 million years. Today's changes in carbon dioxide levels are not because of natural causes, but because of people.
Most of the carbon dioxide in the atmosphere today will be there for many years. Some will stay in the atmosphere for thousands of years. This means that we will see the effects of this carbon dioxide for many years to come.
CHAPTER SIX
The risks of climate change
Acidic oceans
The high levels of carbon dioxide in the atmosphere are having a bad effect on our oceans. Across the world, oceans are becoming more acidic. The last time the oceans on Earth were so acidic was about 250 million years ago. At this time, a huge number of animals became extinct.
About 30 percent of the carbon dioxide people put into the atmosphere goes into the oceans. This stops so much carbon dioxide staying in the atmosphere. Ocean sinks stop the temperature on Earth from getting even higher, but they also make the water in the oceans more acidic.
Scientists are starting to understand the effects that acidic water has on the animals that live in the ocean. Many of the very small animals in the ocean, like corals, are really important for other ocean animals and for people. For example, people eat a lot of fish, and these fish eat smaller fish and other small animals in the ocean. If the numbers of these smaller animals get very low because they are killed by acidic water, there will be lower numbers of bigger fish. This could then cause a problem for all the animals that live in the ocean, including those that people eat.
So, acidic oceans may cause a big problem for people, too. Lower numbers of fish and other sea animals will make life very difficult for communities that live near the sea and catch and sell them as food. It will also make food that comes from the sea more difficult to buy and more expensive.
Coral reefs are in danger
Acidic oceans and warmer seawater are both very bad for corals, and many corals are dying in oceans across the world. Storms, dirty seawater and other ocean animals also damage coral reefs. People are now very worried about the future of the oceans' beautiful coral reefs, including Australia's Great Barrier Reef.
The risk of large climate changes
As the world gets warmer, there is a risk of large and dangerous changes to the Earth's climate. And, once these changes happen, we may never be able to go back to the climate we have today.
Even small increases in temperature can have a big effect on the thick ice over Greenland and West Antarctica. If this ice melts, it will cause sea levels to increase, maybe by many metres. This would have a huge effect on the land next to the sea all around the world.
Studies show that the ice in Greenland is melting more every summer. There is also information to show that the thick ice in West Antarctica is melting and that the damage to the ice is very large. Some scientists think we may never be able to stop this ice melting.
Changes to rain patterns can cause forests to become very dry, and this can increase the risk of fire. Fire and drought can really damage thick forests. Then the forests may become dry land, with only grass and no trees. This land cannot hold as much carbon, so more carbon stays in the atmosphere. This increases temperatures and causes more changes to rain patterns. Many people are worried that this cycle may cause many of the trees in the Amazon rainforest to die.
There are many other large changes to the climate that may happen in the future. These include huge droughts, huge changes in natural rain patterns and huge changes in the ocean. The ocean moves warm and cold water around the Earth, and this has a big effect on the climate. Changes in how this water moves can cause huge changes to the climate in different parts of the world.
Scientists are also worried about the increase in temperature in the Arctic. The Arctic holds a large amount of the greenhouse gas methane (CH4). As the temperature increases, this methane can get into the atmosphere. This is a huge problem because methane is a much stronger greenhouse gas than carbon dioxide.
