By Henrik Svensmark and Nigel Calder – The Chilling Stars - Overview
(Some construction is going on here – by the Al Gore of HTML – me. Please pardon the dust; I don’t think it will cause global warming).
The Climate is always changing. The first clue that cosmic rays have something to do with it comes in Chapter 1, from the alternating episodes of warmth and cold over the past few thousand years. Most recently, the Little Ice Age, which peaked around 300 years ago, has given way to the present warm interlude.
The Little Ice Age coincided with an unusual state of the Sun, known as the Maunder Minimum. Sunspots were very scarce, a symptom of feeble magnetic activity. A jump in the production rate of radiocarbon atoms and the other long-lived tracers, made by cosmic rays in nuclear reactions in the air, was another indicator. We’re shielded from manyg of the cosmic rays by the Sun’s magnetic field, but when it weakens, more of them can reach the Earth.
Chilling events like the Little Ice Age have occurred nine times since the most recent ice age ended 11,500 years ago, always associated with high counts of radiocarbon and other tracers. Historians and archaeologists testify to the misery caused to our ancestors. Reaching further back in time, into the ice ages, a German scientist found stones dropped onto the ocean floor by armadas of icebergs during a succession ov very cold spells. Again, these coincided with low solar activity.
Among scientists who already agree that the Sun plays a prominent role in climate change, opinions differ about how it exerts its influence. Some want to explain the alternations of warm and chilly periods by changes in solar brightness. For them, the cosmic rays play no direct part in the weather but merely signal whether the Sun is more or less active, magnetically speaking, and therefore more radiant or dimmer. On the other hand, Danish scientists led by your author Svensmark think that a direct climatic role is more important, because cosmic rays affect the world’s cloudiness.
Chapter 1 ends with an outline of the strongest evidence against the Svensmark theory, assembled by a Swiss physicist. About 40,000 years ago the Earth’s magnetic field became very weak. Geophysicists call it the Laschamp Event. As a result, many more cosmic-ray particles entered the atmosphere, and left the atomic tracers of their passage. According to the theory of cosmic rays and clouds, shouldn’t they have caused a severe cooling? But that didn’t happen.
To rebut this well-reasoned argument, Svensmark looked again at the adventures of the cosmic rays, as related in Chapter 2. You don’t notice it, but about twice a second a cosmic-ray particle whizzes through you head and disappears into the ground under your feet. When you climb a mountain, or fly in a jet plane, the rate is much higher.
Cosmic rays seemed like an optional extra, after an Austrian scientist detected them nearly a century ago. They were of great interest to scientists, certainly but perhaps unimportant in the domestic economy of the Universe or the Earth. Only recently have astronomers realised that cosmic rays are an essential ingredient in the witch’s brew from which come stars, planets and the chemicals needed for life. And in ways that the experts have been slow to appreciate, the commic rays arriving here from a distant chorus of exploded stars continue to influence our lives.
(10 more paragraphs coming . . .)