Radio signals carry energy

The greenhouse effect

In a greenhouse, vegetables or flowers can thrive even when it's cold outside. That's because greenhouses are built out of glass. The glass - or a transparent film - allows the short-wave rays of the sun to enter the interior unhindered: the air warms up. On the other hand, the glass is impermeable to long-wave heat radiation, so the heat can no longer get out. That’s why it’s cozy and warm in a greenhouse.

Something similar is happening on a large scale on Earth. The greenhouse gases carbon dioxide (CO2) and water vapor are naturally present in the atmosphere. Water vapor enters the air through evaporation, carbon dioxide through the exhalation. Volcanic eruptions also contribute to the natural carbon dioxide content of the air. Both gases have the same effect as the glass in a greenhouse: They allow the short-wave rays of the sun to penetrate to the earth. At the same time, like an invisible barrier, they hinder the long-wave thermal radiation on its way back into space. The heat builds up and the atmosphere heats up.

Without this natural greenhouse effect, life on earth would hardly be possible, because it would be far too cold for most living things. Instead of the current average temperature of plus 15 degrees, it would be an icy minus 18 degrees Celsius. The surface of the earth would be frozen!

The problem starts when we increase the amount of greenhouse gases in the atmosphere. This is mainly done by burning oil, natural gas and coal. Heating the apartment, driving a car, burning garbage: all of these processes emit carbon dioxide. This CO2 has the largest share in the man-made greenhouse effect. But the cultivation of rice or cattle farming also intensify the effect: large amounts of methane (CH4) - also a greenhouse gas. In addition, nitrous oxide, ozone and fluorocarbons are among the greenhouse gases. Because all these gases slow down the heat radiation of the earth, the temperatures on our globe continue to rise.

A shell made of gas

Seen from space, it appears like a fine bluish veil that surrounds the earth: the atmosphere. It is the envelope of air that surrounds our planet. Compared to the diameter of the earth, this shell is quite thin: if the earth were the size of an apple, the atmosphere would be about the thickness of its shell.

Without the atmosphere there would be no life on this planet, because plants, animals and humans need air to breathe. It protects us from the cold and from harmful radiation from space. It also lets meteorites burn up before they can hit the surface of the earth. This atmosphere is vital to us - but what is it actually made of?

The atmosphere is a mix of different gases. A large part of this gas mixture is nitrogen: At 78 percent, that's almost four fifths of the entire atmosphere. Only 21 percent consists of oxygen, which we need to breathe. The remaining one percent is made up of various trace gases - gases that only occur in traces in the atmosphere. These trace gases include methane, nitrogen oxides and, above all, carbon dioxide, or CO for short2 called. Although the CO2-Proportion is quite low, this trace gas has a tremendous impact on our earth's climate. This can be seen in the greenhouse effect, which is heating up our planet.

The fact that the earth has an atmosphere at all is due to gravity. It holds the gas molecules on earth and prevents them from simply flying out into space. In fact, the air becomes thinner and thinner with increasing altitude and thus decreasing gravity. Even at 2000 meters above sea level, this can become uncomfortable for people: He suffers from altitude sickness with shortness of breath, headaches and nausea. Extreme mountaineers who want to climb high peaks like the 8000m in the Himalayas therefore usually take artificial oxygen with them on their tour.

The effect of sunlight

It's unimaginably hot inside the sun: it's 15 million degrees here. After all, it is still 5,600 degrees Celsius on the surface of the sun. This means that the sun is incandescent and appears to our eyes as a white ball.

Without the sun there would be no life on this planet, at least not as we know it today. The sun is a gigantic source of energy that radiates light and warmth into space. Some of their radiation also reaches the earth. This energy warms our atmosphere, the earth and the oceans.

The sun heats the area around the equator the most, because there its rays hit a relatively small area perpendicularly. The poles, on the other hand, reach the sun's rays at a flatter angle. Here the solar energy is therefore distributed over a larger area; and in these regions it stays cooler. The different levels of solar radiation ensure different climate zones. Seasons and weather are also the result of different levels of solar radiation.

If the earth were to store all of the solar energy, it would be unbearably hot here in no time. This can already be felt on a hot summer's day when the temperature climbs to 30 degrees Celsius in a very short time after sunrise. In order for the climate to remain stable for centuries, the earth has to get rid of about the same amount of solar energy.

This happens through the radiation of the earth into space. About a third of the solar energy is immediately reflected back from the atmosphere, land area, bodies of water and ice masses. The earth initially absorbs the rest of the energy in the form of heat. It then slowly releases this heat back into space in all directions.

Are there other inhabited planets?

The earth - the planet we live on - is just one of several planets orbiting the sun. And the sun is only one of billions of stars in space. The question arises: Do the other stars also have planets? And is there life on other planets?

What does it look like on our direct neighbor planet? "Martians" have always been a popular topic in stories and films. But at least since the first probes landed there and sent measured values ​​to Earth, we have known that life as we know it is not possible on Mars.

There are very special conditions on earth: it is not too cold, but also not too hot, so that there is liquid water. And the earth is heavy enough to hold an envelope of air. So we can breathe and are protected from radiation and meteorite impacts. Sunlight provides sufficient energy, there are seas, a solid area of ​​land and all the chemical elements and compounds necessary for the construction of living beings.

Earth is the only planet in our solar system on which all of these conditions are met: Mercury and Venus are closer to the sun and therefore too hot. Mars is not heavy enough and therefore has no atmosphere. And the outer planets are too cold because they don't get enough energy from the sun - and the gas planets also lack a solid surface. So in the solar system only the earth remains as an island of life.

So scientists are investigating whether other stars have planets - and whether there could be life there. But that's not that easy, because even the closest stars are so far away that even with the best telescopes you can't see any planets. Only indirect clues reveal the planet - for example, when the star's light darkens for a short time because the planet passes right in front of the star. With this and other tricks several thousand such “exoplanets” have been discovered - but a “second earth” comparable in every respect was not yet among them.

Even if you find one: the question of whether it is on this planet intelligent Life cannot be answered in this way. That is why scientists started the SETI project to search for radio signals from space. The abbreviation stands for " for E.xtraterrestial I.ntelligence “- search for extraterrestrial intelligence. The idea: if an alien civilization similar to ours develops technology, they may also use radio waves. These could spread into space and maybe reach our antennas. The only question is whether these radio waves can even reach us - and whether we are listening in the right direction at the right moment.

But most scientists are convinced that there are other intelligent life forms somewhere in space. If we were alone in the universe, says SETI founder Carl Sagan, it would be a terrible waste of space.

Why are there ice and warm periods? Natural climate changes

At the height of the last great ice age it was bitterly cold. So cold that a third of the land area disappeared under thick layers of ice. All of this was about 20,000 years ago. Over the millennia, temperatures rose again. Today we live in a warm period and only ten percent of the land area is icy. But it was far from the first climate change on our planet. Since the earth was formed 4.6 billion years ago, it has sometimes been warmer and sometimes colder - without any human involvement. But why?

Climate researchers have long been trying to find out what causes natural climate change. One explanation for this is that the earth "wobbles" a bit as it orbits the sun. You can imagine it to be similar to a top, only on a much larger scale. Both the inclination of the earth's axis and the orbit of the earth shift over the course of millennia, in a regular cycle. This “egg” also changes the amount and distribution of the irradiating solar energy. As a result, temperatures fluctuate over long periods of time and lead to ice and warm periods.

The distribution of the continents also plays a role in the fluctuations. Because their position has shifted constantly in the course of the earth's history. When large land masses reached the North or South Pole, huge amounts of ice could accumulate there. The ice reflected a large part of the sun's rays, it got even colder. Only when the continent moved away from the Pole did the temperatures rise and the end of the Ice Age was in sight.

The composition of the atmosphere also affects the climate. The greater the proportion of greenhouse gases such as carbon dioxide or water vapor, the more the atmosphere heats up. Their gas mixture can be changed by natural processes, for example by a volcanic eruption. When a volcano spits fire and ashes, tiny particles are thrown high into the air, the aerosols. They reflect the sun's rays before they reach the surface of the earth. The temperature on earth is falling - at least for a short time. The eruption of the Tambora volcano in 1815 was followed by a “year without a summer”. Back then, in the middle of the warmest season, snowstorms swept across the country on the east coast of North America. The consequences were catastrophic crop failures.

In contrast to these natural climate changes over the course of history, the current climate change is caused by humans. The fact that the average temperature has been rising for a good 150 years is mainly due to the fact that people are producing more and more carbon dioxide.

The consequences of climate change

Climate change is already clearly visible in the polar regions. Just a few decades ago, the Arctic Ocean was largely covered by ice. But this ice sheet is melting due to the rising temperatures: in the last 30 years its area has almost halved. At the same time, the ice layer is getting thinner and thinner. Climate researchers have calculated that the ice could melt completely in the next 20 years. The sea level would rise by a few meters as a result. But it's not just the ice sheets on the poles that are melting. The high mountain glaciers are also losing mass.

Because the sea level rises as the ice melts, ever larger coastal areas are flooded. Low-lying island states, such as the Maldives in the Indian Ocean or Tuvalu in the Pacific, are therefore increasingly threatened by storm surges. And not only the sea level, the water temperature also rises with climate change. As a result, more water evaporates and more water vapor is stored in the air. This increases the greenhouse effect, which further heats the atmosphere. This also increases the risk of severe weather such as heavy rain and hurricanes.

In arid regions, the deserts are spreading due to rising temperatures. More and more droughts are causing rivers to dry up and areas of land that were previously green wither. In the south of Spain, for example, the usual rainfalls, which are urgently needed for agriculture, have been absent for years. And the water shortage in southern Europe continues to intensify.

All of these consequences of climate change can already be observed. Climate researchers are trying to calculate how things will continue with the help of computer models. But the future is difficult to predict because so many influences determine our climate. The salty sea water is diluted with fresh water by the melting of the glaciers. However, the salinity of the sea drives the ocean currents. So what could happen if the warm Gulf Stream breaks off due to the lower salt content? Will it be colder instead of warmer in Europe? What would happen if the permafrost thawed in the far north? Do tons of the greenhouse gas methane then escape from the ground? And will it accelerate climate change?

So far nobody can answer that exactly. With all the unanswered questions, one thing seems certain: if we don't drastically reduce our carbon dioxide emissions, the temperatures on this globe will continue to rise.


Global carbon dioxide emissions have never been as high as they are today. In 2010, it actually rose more sharply than ever before. This has now been announced by the US Department of Energy. The numbers exceed even worst fears.

For years, experts have warned of the speed of global warming. Apparently without success: The proportion of the climate-damaging gas carbon dioxide in the air is increasing rapidly. In the industrialized countries in particular, it gushes continuously from chimneys and exhaust pipes. The new numbers are frightening: In total, the world emitted over 33,500 million tons of carbon dioxide in 2010. That is 1,900 million tons more than in the previous year, an increase of six percent!

According to the US study, China and India are primarily responsible for the increase in horror. The two countries are on a growth path economically. They get their energy primarily from coal-fired power plants - and thus produce a lot of CO2. Overall, China is the record holder for greenhouse gas emissions, followed by the USA, Russia and India.

The policy for global climate protection has so far failed completely. China and the US refuse to sell their CO2- to reduce emissions. Russia, Canada and Japan also no longer want to comply with guidelines if the main polluters are reluctant to comply with international limit values. Bad for the climate, as the new study clearly confirms on the basis of the figures.

The Keeling curve

The first CO2-Measuring station in the world was opened far away from car exhaust fumes and factories: In 1958, the American climate researcher David Keeling began to regularly measure the carbon dioxide content of the air on the Mauna Loa volcano on the island of Hawaii. This place was chosen deliberately. Because neither chimneys nor forests influenced the result, an average value of the trace gas in the air could be measured here. A second station in Antarctica also met these conditions. After two years, Keeling presented his results to the world: The level of carbon dioxide in the air increased! In the following years, Keeling continued to fight for regular CO2-Measurements of the atmosphere. With success: The result is the so-called Keeling curve, a collection of data that continues to record the carbon dioxide content of the air and the significant increase in CO2 documented.