And then people could ice skate on the Thames.
It should be noted that in Western Europe, “the summers were not all that unusual,” according to Ammann. This indicates that whatever caused this intense pulse of cold weather was restricted to winter, which is consistent with the above series of events.
Like I said, this is complicated. But that’s the whole point. If it were simple, we’d understand it better, and no one would be arguing over how the Sun affects the climate. In fact, these events are all fairly well established in general, but the problem is the magnitude of each one. How much less ultraviolet light was emitted by the Sun during the Maunder Minimum? How much less ozone was created? How far did the jet stream dip south? How much sulfur was spewed into the air by volcanoes? Changing any one of these inputs makes the results different, so knowing how much each one affects the climate is very difficult to figure out.
The important thing to remember here is that while the Sun affects our climate, changes in its total output over the eleven-year magnetic/ sunspot cycle are small. There is a definite effect on the Earth, but it’s more like a priming charge than the explosion itself. It requires other catastrophic effects—volcanoes, asteroid impacts, man-made emission of CO2 and methane—to take advantage of the Earth’s climatic sensitivity and cause a disaster.19 And even then, at least in this particular case, the problems tend to be regional. The global environment of the Earth doesn’t change that much.
That’s cold comfort to people who are affected, of course. And if the particular region is very sensitive—or that region has global impact itself—then the results can be much worse. A decades-long series of brutal winters in the United States, for example, or China, could cause famine and economic depression. Wars start over such things, and modern wars can wreak far more damage than a simple solar minimum. When it comes to potential extraterrestrial sources of destruction, the last thing we need to do is add our own capabilities to them.
A more pertinent thought is: could another such minimum occur again? Yes, it could. Worse, it doesn’t look as if such events are entirely predictable. Scientists studying the occurrence of long minima in sunspot numbers show that they don’t appear at regular intervals, meaning they are not an inherently predictable phenomenon in the long term, although it’s marginally possible to make predictions about the very next sequence in the solar cycle. So we might be headed into another minimum a few cycles from now, or it might not happen for a thousand or ten thousand years. But it seems very likely indeed that it will happen again.
HOT PLANETS AND HOT AIR
So if the Sun can indeed affect Earth’s climate, what about global warming? Is it caused by the Sun, and not by humans?
A lot of noise has been made on this topic, but scientists actually do agree on this: the Sun is not the cause of the current temperature rise seen in the latter half of the twentieth century to today.
This isn’t hard to show, actually. The amount of radiation from the Sun is measurable, and since the 1950s to today there has not been an increase in solar radiation. In other words, the Sun has not been getting brighter during the time when the Earth has been getting warmer. The amount of solar radiation has been quite steady since 1950, and is obviously not the cause of global warming. It’s clear to the overwhelming majority of scientists independently studying this phenomenon that it is human activity, our activity, that is behind the current sharp rise in global temperatures.
This most basic fact has not stopped some people from claiming that many other planets are also experiencing global warming, and therefore the cause here on Earth cannot possibly be human-induced. The only thing linking all the planets is the Sun, they say, and therefore the Sun is causing this warming.
However, this is nonsense. The claim is that Mars, Jupiter, Triton (a moon of Neptune), and even Pluto are warming.20 However, each of these has separate causes, linked with the individual objects’ atmosphere and orbit, and any purported warming is not related to the Sun.
And let’s be clear: these objects are much farther from the Sun than the Earth, and receive proportionately less heat. To warm up Pluto even one degree, the Sun would have to get so much brighter and hotter that it would be overwhelmingly obvious—in fact, the Earth would get totally fried. Since our own warming is less than a degree, it’s clear that the other planets’ warming must be due to some other source than the Sun.
SUNNY OUTLOOK
We live on a small planet where a considerable number of factors have to align to make life hospitable. However, we live near a tempestuous star that will, inevitably, do what it can to disrupt that equilibrium. Ironically, too much solar activity can cause immediate and global damage, but too little can, in the long run, be just as bad. Like most things in the Universe, this is a delicate balance, and a swing to either side would be catastrophic.
However, we have survived many small oscillations. The Little Ice Age came and went, with people taking it in stride—they really did skate on the Thames. Huge flares have wreaked havoc on our power grids, and with a little care, foresight, and a pile of money, we can avoid total disaster.
As for the big swings . . . well, we’ll see. They may not happen for centuries or even millennia, and by then we may be able to take action. But the time to start thinking about it all is right now; and we are. Smart people are working on these very topics, and while it may take time to figure out all the angles, and there may be lots of arguments along the way, I think in the end we’ll figure a lot of this stuff out.
In the meantime, I’ll still enjoy the occasional sunny afternoon . . . but I’ll also be mindful that over my shoulder, just an astronomical stone’s throw away, is a vast and mighty star. And it has a temper.
CHAPTER 3
The Stellar Fury of Supernovae
THE FIRST ONES TO NOTICE ARE PROFESSIONAL astronomers.
Researchers at the Super-Kamiokande neutrino observatory in Japan are shocked when their detectors light up like Christmas trees. Such unprecedented readings prompt them to look for malfunctions in their hardware, because surely no astronomical event could generate so many of the ghostly subatomic particles—even the Sun, the brightest object in the sky, barely produces enough neutrinos to be picked up by their instruments. There would have to have been millions of neutrinos detected to register so strongly! Poring over their instruments, it takes them nearly two hours to figure out that the flood of neutrinos was indeed real, which was far too late . . . not that advance knowledge would have helped.
Within minutes of the event, automated observatories orbiting the Earth perk up. Astronomical satellites designed to observe high-energy light such as X-rays and gamma rays see a rise in detections. One by one, as they slew over to focus on the source of the particles, their detectors saturate with photons as the fierce light intensifies. Within minutes the satellites are blinded, overwhelmed with light, and lose track of the target.
On the ground, across the night sky of Earth, thousands of amateur astronomers, truckers, police officers, and general night owls notice the light in the sky. It’s getting brighter by the minute. Some of the amateur astronomers momentarily think it’s an airplane, or the glint of reflected sunlight off an orbiting satellite. But many immediately realize what’s happening, and start taking data. Others send out e-mails, alerting astronomers all over the world. Get out your scopes! There’s a new supernova!
But the e-mails are unnecessary. Within minutes, the “new” star is so bright that other stars in the sky can’t compete. Like the sunrise or the full Moon, the supernova is washing out the sky around it.
Astronomers are beside themselves with glee. It’s been over four hundred years since the last naked-eye supernova in our galaxy, and this one will no doubt be a record breaker.
But their joy is short-lived. In the middle of their observations, all their machines suddenly lose power. The images and data are all lost when the computers controlling the telescopes die. And before they can properly assess the problem,
all the power goes out. One astronomer ventures outside to see what’s going on and realizes that the glow of the nearby city is gone. Normally, the combined luminescence of thousands of streetlights, buildings, spotlights, car dealerships, and house lights drowns out the fainter stars in the sky. In a huge ironic twist, the power is out everywhere and the sky is truly dark for the first time in years, yet she cannot observe because her power is off too. Her telescope is useless.
She stares upward at the stars and, after a few minutes, realizes the sky isn’t as dark as it was earlier: the fierce eye of the supernova is glaring down on her, and the sky around it is blue. No other nearby star could possibly compete.
Her attention is diverted when she sees another bright light in the sky, this one moving slowly across the ever-bluer sky. She realizes it’s the International Space Station. She laughs, glad to see something normal for a moment.
What she doesn’t realize is that the astronauts on board are dead. Had she known, she certainly wouldn’t have smiled. But then, in a few years, everyone on Earth will be dead too. Humans were doomed from the instant the first rays of light from the supernova touched the atmosphere.
Gamma rays from the supernova destroy vast amounts of ozone, which is quickly reduced to half its normal amount. When the Sun rises in the morning, its ultraviolet light will stream all the way through the atmosphere nearly unabated. Severe sunburn will be the least of the problems faced on Earth as the UV radiation kills off the ocean’s phytoplankton, which make up the base of the food chain. Animals that feed off phytoplankton find their food source dwindling and eventually disappearing in mere days, and animals that feed off those animals face the same dire problem a few days later. This die-off marches up the food chain, and it won’t stop until it reaches the top: us.
It’s been a long time since an astronomical event touched off a mass extinction. But now, another one is under way.
A STAR IS BORN
If you go outside on a dark, clear night, far from city lights, you can see thousands of stars sprinkled across the sky. They may seem unchanging, fixed—some people even refer to the night sky as the “starry vault,” implying a strength and permanence. Sure, the stars rise and set, but that is a reflection of the Earth’s motion, not theirs. They twinkle too, but again the fault lies in ourselves and not the stars—they flicker because the ocean of air above our heads blurs their light.
Even if you go out night after night, week after week, you may not see any changes in the stars. A sharp-eyed observer may note that some stars subtly and periodically change their brightness; these so-called variable stars wax and wane over days and weeks. But the stars themselves neither appear nor disappear, and do very much seem as permanent as the night sky itself.
But the Universe is deceiving. Things do change, and sometimes that change can be dramatic. On July 4, 1054, a new star appeared in the sky in the constellation of Taurus. Chinese astronomers recorded this “guest star,” noting that it appeared to be even brighter than the planet Venus, which is third only to the Sun and the Moon in our sky. There are records scattered throughout the world of the appearance of this new object, though they are spotty and not without some controversy, but there is no doubt about the reality of the event.
Today, a thousand years later, if you use a pair of binoculars to scan the sky in the constellation of Taurus between the horns of the bull, you might note a faint fuzzy blob that is clearly not a star. A small telescope can back up this observation. A big telescope—especially one equipped with a camera capable of taking long time exposures—reveals this object to be a gaseous and filamentary cloud. It looks like the aftermath of an explosion. In fact, images taken many years apart reveal the gas cloud (called a nebula by astronomers, from the Latin word for “cloud”) to be expanding; filaments and knots in the cloud have obviously moved outward in the intervening time. Backtracking the expansion shows that all the gas originally came from one point in the sky, the position of which is marked by a star very near the center of the cloud, indicative of a single explosive event. By measuring the speed of the expansion, the date of this event can be estimated. Remarkably, that date is the mid-eleventh century, suspiciously close to when the Chinese guest star was observed. Today, no astronomer on the planet doubts that the two events are the very same thing.
The Crab Nebula is the expanding debris from a massive star that exploded in July 1054. It is perhaps the best-studied object in the sky, and one of the most beautiful.
NASA, ESA, J. HESTER AND A . LOLL (ARIZONA STATE UNIVERSITY)
What the Chinese saw was one of the largest and scariest events in astronomy: a supernova. It might not have seemed all that scary at the time—after all, it was just a light in the sky! But upon closer examination the magnitude and scale of the event are revealed.
The gas cloud—called the Crab Nebula because of its current dubious resemblance in a small telescope to a crustacean—is the expanding remnant of this stellar explosion. In the subsequent millennium since its creation the cloud has grown to trillions of miles in diameter. The gas is still ferociously hot, heated to thousands of degrees by the shock waves generated as it expands supersonically and rams into the cooler gas surrounding it. Energy also continues to be poured into the cloud by the emanations from the central star, the cinder left over from the explosion.
The distance to the Crab is an estimated 6,500 light-years, or about 40 quadrillion (40,000,000,000,000,000) miles, and yet even at such a distance, and after ten centuries, it is one of the brightest nebulae in the sky. At the time, the supernova event itself was bright enough to be seen in full daylight, indicating that in just a few weeks the explosion released awesome amounts of energy into space—as much as the Sun will put out over its entire lifetime of 12 billion years. In fact, a typical supernova can easily outshine the combined light from all the hundreds of billions of stars in an entire galaxy, and persist that way for weeks.
Our eyes can only see visible light, a very narrow slice of the energy band of light called the electromagnetic spectrum, which includes radio waves, infrared, ultraviolet, X-rays, and super-high-energy gamma rays. If you had X-ray eyes, the Crab would be one of the brightest objects in the sky. The same is true of radio waves, and if you could see in gamma rays, the Crab would be the single brightest persistent object in the sky.
I’ll gently remind you that the Crab is 400 million times farther away than the Sun.
Clearly, supernovae are awesome events capable of wreaking destruction on a vast scale. At its remote distance, the explosion that generated the Crab Nebula was little more than a pretty light in the sky, but not all supernovae are so far away. In fact, the Earth has had close shaves with exploding stars in the past, and there will certainly be more in the future.
But how close is too close? To understand just what a supernova can do to its environment and just how these events can be a danger to us on Earth, we’ll have to understand what would make an otherwise stable star explode.
Hubble snapped this picture of Supernova 1994D, the fourth exploding star seen in 1994. The host galaxy is called NGC 4603, and is located a very safe 100 million light-years from Earth. The supernova was about as bright as the entire galaxy.
NASA AND J. NEWMAN (UC BERKELEY)
THE LIFE OF A STAR
While ancient astronomers were baffled by the stars in the night sky—were they holes in the vault of the sky, letting the radiance of the Sun through?—we have a pretty good understanding of them now.
Stars are not just points of light—each is a sun in its own right, most smaller but some fantastically larger and more luminous than our Sun. What a revelation that must have been, the first time someone realized that stars are suns, but terribly far away!
As astronomers studied stars, slowly and inevitably they learned more about them. Some stars are red, and some are blue (you can see this with your own eyes by examining a handful of the brightest ones), which indicates that they have different temperatures: red stars are
cooler, blue stars hotter. Many stars are not individuals, but instead are pairs of stars orbiting each other in what are called binary systems, only masquerading as single stars because of their remote distance. Using laws of physics established by the astronomer and mathematician Johannes Kepler in the seventeenth century, astronomers could determine the masses of the stars in binaries, opening the door to an understanding of the physical processes inside them.
At the most basic level, a star is a big ball of gas, and so its behavior is in many ways simple. As a gas is compressed its temperature will rise. A ball of gas with the mass of the Sun will compress under its own gravity, heat up, and shine brightly, but it will have a limited lifetime—without an internal source of heat it will cool in about a million years or so.
By the nineteenth century there was mounting evidence the Earth was at least millions of years old, and perhaps even older. And surely the Sun was older than the Earth! Then, in the 1930s, scientists realized that a star is a nuclear furnace, like a vast H-bomb, whose explosion is held in check by the star’s own gravity. Nuclear fusion could support the Sun’s energy output for not just millions but billions of years, solving its age crisis. In an ironic twist, objects as huge as stars are powered by the tiniest of objects: atomic nuclei.
A typical atom is composed of a dense nucleus in its center surrounded by a cloud of negatively charged electrons. The nucleus contains electrically neutral neutrons, and positively charged protons. The number of protons is what gives the atom its characteristic properties: for example, hydrogen has one proton in its nucleus, helium has two, oxygen eight, and iron twenty-six. Under some circumstances (intense heat or absorption of ultraviolet light, for example) electrons can be removed from an atom, but it’s the number of protons in the nucleus that defines the atom.
Death From the Skies!: These Are the Ways the World Will End... Page 7