The history of climate change

Catastrophe: Earth gets hotter and hotter. Nah, the climate of the earth has always varied. This is totally normal... Man has altered the environment! ... Sometimes it's ice age, sometimes it's warm.

It'll turn again. Perhaps you have heard that there are opinions about global warming: ... that research is doubtful. There are those who say that the climate of the earth has always varied. Sometimes it's warmer, sometimes colder, and there is nothing to worry about.

Is there any truth to that? -- In one aspect it is correct. The average temperature on earth has changed. When researchers study really long periods of time, over hundreds of millions of years, it turns out that the earth sometimes has been warm and completely ice free. And sometimes, huge, thick ice caps have extended from the poles. Some scientists even believe the entire earth was once covered with ice, like one vast snow ball.

So, the temperature on earth has changed between warmer and cooler, over long periods. What's the reason for these changes? There are several explanations. The earth doesn't always keep the same distance from the sun. Earth's orbit round the sun changes shape, from being almost circular, ...

to being much more oval, with a larger distance from the sun during some periods. A larger distance means less sun energy hits the earth. Earth gets cooler. And also the atmosphere is of great importance: the mixture of gases in the atmosphere. This has varied during the course of millions of years.

When there is a large portion of greenhouse gases in the atmosphere, such as methane and carbon dioxide, the earth is heated up. When the portions decrease, the earth gets cooler. And when the portions increase again, the earth gets warmer. One such change in the constitution of the atmosphere started to occur about 50 million years ago. The earth was very warm at this time.

The heat meant great conditions for a particular fern, that lived in water. Ferns of this kind grew and reproduced in huge numbers. And green plants bind carbon dioxide and release oxygen. So, when these ferns died, and sank to the bottom of the ocean, they took carbon dioxide from the atmosphere with them. This lowered the greenhouse effect on Earth.

The average temperature decreased, and the Earth entered a cooler period. But all these are slow changes over a long time. Hundreds of millions of years. Look at the diagram. The horizontal axis, represents time.

One hundred million years ago, two hundred million, and so on. -- The vertical axis shows the temperature on earth. And the curve shows how the temperature has changed during the course of history. It goes up, and down. Warmer periods are followed by cooler ones. But a change of temperature doesn't have to take several million years.

There are also smaller and faster changes, that only take something like a thousand years, or even less. As you can see in this diagram. It's the same sort of diagram that we just saw. The horizontal axis shows time, with the start at 11,000 years ago... ... and the end today.

The 'y' axis shows the average temperature. -- And the curve shows how the temperature has changed during the last 11,000 years. It goes up... and down... And suddenly... a hundred years ago, something happens.

The curve turns steeply upwards. Nowhere else on the graph is the curve so steep. This means that never during this time has the change in temperature been so fast... as now. The temperature on earth is currently increasing faster than ever.

Do you remember the question we asked in the beginning? Is this global warming just part of the normal variation on earth? There is the answer to the question. What we are seeing now is not one of the normal temperature changes on earth. The curve is too steep.

The temperature is rising with a speed unique in the earth's history. But why? It's a change in the atmosphere that's doing it, in particular higher proportions of greenhouse gases. -- What will happen in the future? -- As long as humans keep releasing greenhouse gases into the atmosphere, the average temperature on earth will increase. By how much? How fast? -- What headlines will we see in the future's news?

We don't know. It all depends on what we humans together succeed in doing to slow down these emissions.