Death from the Skies! (9 page)

The problem is, the NO
₂
can oxidize in the atmosphere to form nitric acid. When this dissolves in water droplets, acid rain can result, with terrible effects on the Earth’s ecosystem. This did not appear to be a major problem from the 1859 event, but if in the future more energetic eruptions impinge on our atmosphere, we may be able to measure the effects of that as well. That’s just another fun way the Sun can slam us.

With all this talk of magnetic storms, flares, and CMEs damaging the Earth, are we missing something more obvious? The Sun is, after all, far and away the major source of heat in the solar system. While the Sun seems rock-solid in its energy output, we have already established that it’s a variable star. Sunspots wax and wane on an eleven-year cycle; could this possibly lead to a change in the amount of energy we receive from the Sun? And if more or less sunlight hits the Earth, could that then lead to climate change on Earth, and a potential mass extinction?

It should be noted immediately that time and again, people have tried to tie the Sun’s eleven-year cycle with events here on Earth. The stock market, baseball scores, even personality traits have been (dubiously at best) linked to sunspot numbers. The problem is, if you look at enough cycles, some are bound to line up superficially. You have to be able to separate the wheat from the chaff, which can be very difficult.

Scientists have been arguing for years over whether there is some correlation between solar activity and weather on Earth. It seems that there is, but the factors involved are subtle and difficult to pin down. If they were clear, there’d be nothing to argue over. However, there are some connections that appear to be firmly in place . . . and sunspots do play a role. But the direction of that role might surprise you.

Sunspots are dark, cooler patches of the Sun’s surface. You might think, then, that if there are lots of sunspots, we get less light and therefore less heat from the Sun. So, lots of sunspots equals cooler climates.

But spots are only dark in
visible light.
There are bright regions surrounding sunspots called
faculae
(literally, Latin for “little torches”) that form because of the complicated connection between the Sun’s surface magnetic field and the hot gas bubbling up from deeper regions. The gas in the faculae is hotter, and therefore brighter. On average, sunspots are 1 percent darker than the Sun’s surface, but faculae are 1.1 to 1.5 percent brighter. This means that when the Sun is covered in spots, it’s actually
brighter
in visible light than it is when there are fewer spots!

The primary source of heat for the Earth’s surface is the visible light from the Sun. Studies have shown that when the Sun is at the peak of its cycle—when sunspots and faculae are more prevalent—the overall solar irradiation of the Earth increases by just about 0.1 percent. This is a small but significant increase—it causes a global temperature increase on Earth of about 0.1 to 0.2 degree Celsius (about 0.2 to 0.4 degree Fahrenheit). The opposite is also true; during the sunspot minimum, the Earth’s average temperature decreases by a fraction of a degree.

Let’s face it: this is a pretty small effect. By itself, it hardly changes anything on Earth. However, heating of the Earth’s surface from the Sun is only
one
way the climate can be affected. There are lots of other sources of climate change, as we are now all too aware. In many cases, these sources
by themselves
don’t do much to the climate.

But what if two or more of these effects add up?

Things can get bad. We need only to look back in time a short way to see how.

The existence of sunspots had been known for centuries, even before the invention of the telescope. But once telescopes were trained on the Sun, the view naturally improved. People have been monitoring the size and number of sunspots nearly continuously since the early 1600s.

In 1887, an astronomer named Gustav Spörer noticed that the records of sunspots appeared to show an absence of spots between the years 1645 and 1715. For literally seventy years, the Sun’s face was virtually blank, clean of solar acne. In the late 1800s, the scientist E. W. Maunder summarized Spörer’s findings and published them. We now call this period of sunspot deficit the Maunder Minimum.

All of this would be somewhat academic if not for one rather critical point: the years 1645 to 1715 were also a time of much lower than average temperatures across Western Europe and North America. It was so cold that the Thames River froze over (which it generally does not do, even in winter), glaciers in the Alps advanced, destroying whole villages, and the Dutch fleet was frozen solid in its harbor. This period was called the Little Ice Age.

It’s awfully tempting to directly connect the Maunder Minimum with the Little Ice Age, but we have to be very careful. In nature, it’s rare for a single effect to have a single cause, especially when the effect is as dramatic as a prolonged climate change. Usually, there are a number of events that have to occur to manufacture such a big change.

It turns out the Little Ice Age may have started long before the Maunder Minimum, even as early as the mid-thirteenth century. Caspar Ammann, a solar physicist who has extensively studied the connection between the Sun’s output and the Earth’s climate, notes that the Little Ice Age was not one continuous event, but instead consisted of “several pulses of cooling episodes . . . the first one started in the 1250s through 1300, after a medieval warming period.” Clearly, there were other causes of the temperature drop.

The biggest culprit is probably volcanic activity. There are clear signals of eruptions during the Little Ice Age, mostly seen in ice cores: atmospheric gases trapped in polar ice can be studied to determine what was happening in the Earth’s air during certain times in history. Interestingly, in the 1690s, the Little Ice Age got very severe, especially in Western Europe—there are stories of birds literally freezing to death sitting in branches. At this very time, there is a large spike in the amount of atmospheric sulfur found in ice cores, indicating large levels of volcanic activity. Volcanoes launch sunlight-reflecting dust and gases into the air, reducing the amount of visible light reaching the Earth’s surface. This cools the planet by lowering the amount of heat the surface can absorb.

By itself, this could not cause the severest parts of the Little Ice Age. But together with the Maunder Minimum, when the global temperatures would have dropped, it could have lowered the Earth’s average temperature even more.

Still, if this were a
global
effect, why was Western Europe hit so much harder than everywhere else?

It turns out there is a
third
player in this game. This gets a little complicated, so strap yourself in.

During a sunspot minimum, there is less solar activity in general. Besides there being less visible light, there is a drop in the amount of sunlight across the spectrum, including ultraviolet light. This turns out to be important: UV light is what helps create the Earth’s ozone layer; it turns normal atmospheric oxygen (O
₂
) into ozone (O
₃
). If there is less UV, there is less ozone. Ozone is actually quite important in the temperature balance of the upper part of the atmosphere, called the
stratosphere.
When there is lots of ozone the stratosphere is warm (because it absorbs UV light), and when there is less ozone the stratosphere is cooler.

Most, but not all, of the ozone creation happens in the tropics, at low latitudes near the equator. That’s because that’s the part of the Earth getting the most sunlight, and therefore the most UV. In the summer, ozone can be created both at the equator and at the pole, because that whole hemisphere is in sunlight. In that case, the difference in temperature in the stratosphere from pole to equator is minimal.

But in the winter, the pole is in darkness. No UV reaches the stratosphere, so no ozone is created there. That in turn means there is a big temperature difference in the ozone layer between the equator and the pole.

The problem is that the jet stream is sensitive to these temperature differences. In the winter, the temperature change across latitudes is large. This drives a strong jet stream, which circulates very firmly around the globe. But in the summer, when the gradient is smaller, the jet stream weakens. Instead of making a tight circle, it meanders, flopping down loosely to lower latitudes. When it does this, it can bring cold air from the Arctic to southern locations, and warm air from the south up to higher latitudes.
¹⁸

As it happens, the jet stream tends to dip down more at certain locations on the Earth than others. Western Europe is one such place.

This then is the most likely scenario for the very bitter winter cold snap in the 1690s in Europe: volcanic activity dropped the global temperatures, as did the Maunder Minimum. Together they made things cold, but not brutal. But the drop in solar activity dropped the Sun’s ultraviolet output, which lowered ozone production on Earth. This changed the direction of the winter jet stream, bringing the unusually cold Arctic air down to Western Europe.

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 CO
₂
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.

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.

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.