Carl Sagan's book "Cosmos" was republished in the USA
People who reread it are amazed at how much the famous astronomer and popularizer of science was concerned about climate change in 1980. It seems that he wrote this chapter yesterday. So here is this passage.
The Sphinx - half man, half lion - was built over 5,500 years ago. His face was once sharply defined. Now it is blotted out by desert sands and rains. In New York, there is an obelisk called "Cleopatra's Needle", which was brought from Egypt. Only a hundred years old in Central Park, and now its inscriptions have been almost completely destroyed by smog and industrial pollution - chemical erosion, reminiscent of the processes taking place in the atmosphere of Venus.
Erosion on Earth is gradually erasing information, but so slowly that we do not notice it. Large formations like mountain ranges live tens of millions of years, impact craters perhaps hundreds of thousands, and monumental human creations only a few thousand. In addition to this slow and steady erosion, catastrophes big and small happen. The Sphinx has no nose. Someone shot him: some say they were Mamelukes, others nod at Napoleon's soldiers.
On Venus, on Earth, and elsewhere in the solar system, we see traces of catastrophic destruction caused by slow, monotonous processes: on Earth, for example, sediment carried by streams, rivulets and rivers leads to the formation of huge alluvial basins; there may still be ancient riverbeds on Mars; Io, the moon of Jupiter, has something like wide channels, paved with streams of liquid sulfur. On Earth and in the upper atmosphere of Venus and Jupiter, powerful weather systems are raging.
There are sandstorms on Earth and Mars; lightning on Jupiter, Venus and Earth. Volcanoes fill the atmosphere of Earth and Io with debris. Internal geological processes are slowly deforming the surface of Venus, Mars, Ganymede and Europa, as well as the Earth. Glaciers, especially glorious for their slowness, are reshaping the landscape on Earth and probably on Mars. These processes do not need to be permanent. Almost all of Europe was once covered in ice. Several million years ago, on the site of present-day Chicago, a glacier three kilometers thick rose. On Mars and elsewhere in the solar system, we see formations that could not have appeared today - landscapes created hundreds of millions or even billions of years ago, when the planet's climate was completely different.
There is another factor that can change the landscape and climate of the Earth - intelligent life. Both Venus and Earth have a greenhouse effect due to carbon dioxide and water vapor. The world average temperature on Earth would be below the freezing point of water, if not for the greenhouse effect. Thanks to him, the ocean is liquid and life is possible. A little greenhouse conditions are good. But on Earth, carbon dioxide is found in the earth's crust - in limestone and other carbonates - not in the atmosphere.
If the Earth moved just a little bit towards the Sun and the temperature rose a little, some of the CO2 would escape from the surface rocks, increasing the greenhouse effect, which, in turn, would gradually heat the surface even more. As a result, more carbon dioxide would evaporate from the carbonates and pose the danger of a runaway greenhouse effect and very high temperatures. This is what seems to have happened in the early history of Venus due to its proximity to the star. The surface conditions of Venus warn that a similar catastrophe could happen to a planet very similar to ours.
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The main sources of energy for the current industrial civilization are the so-called fossil fuels. We burn wood and oil, coal and natural gas, and the by-products from the process are released into the air. As a result, the content of carbon dioxide in the earth's atmosphere is rapidly increasing.
Since a runaway greenhouse effect is possible, we need to be careful: a rise in the global average temperature by just one or two degrees could be catastrophic. By burning coal, oil and gas, we also add sulfuric acid to the atmosphere. As on Venus, our stratosphere is already largely saturated with a mist of tiny droplets of sulfuric acid. Our big cities are polluted with harmful molecules. But we do not understand the long-term consequences of our chosen course.
But we are changing the climate in the opposite direction. For hundreds of thousands of years, human beings have been burning and cutting down forests, as well as raising domestic animals that graze in the meadows and destroy them. Slash and burn farming, industrial rainforest deforestation and overgrazing are still with us. But forests are darker than meadows, and pastures are darker than deserts. As a consequence, the amount of sunlight absorbed by the soil is reduced and, as a result of land-use changes, we lower the surface temperature of our planet. Will this cooling increase the area of the polar ice caps, which, due to their brightness, will reflect more sunlight and lead to further cooling of the planet?
Our beautiful blue planet, Earth, is our only home. It's too hot on Venus. It's very cold on Mars. Earth is the only paradise for people. After all, this is where we were born. But favorable climatic conditions may disappear. We are affecting our poor planet in contradictory ways. Whether we will slide into Venus Hell or the Martian Ice Age, no one knows.
Studying the global climate and comparing the Earth with other worlds has just begun. This research is poorly and reluctantly funded. Our ignorance still pulls and pushes the Earth, pollutes the atmosphere and increases the albedo of the planet's surface, regardless of the fact that the long-term consequences of such activities are unknown. Several million years ago, when people appeared, the Earth was already not young, it experienced 4.6 billion years of catastrophes. And people turned out to be a new and possibly decisive factor.
Our minds, our technologies have given us the strength to influence the climate. How are we going to use this power? Are we willing to endure ignorance and complacency in matters that affect all of humanity? Will we value short-term benefits over the well-being of the earth? Or will we think on a different time scale and take care of our children and grandchildren in order to understand and protect the complex life support systems of our planet?
The earth is a tiny and fragile world. She must be protected.