The global climate has been in flux throughout recorded history. Could the changes we see happening today be a result of natural processes that have occurred over millennia? Not a chance, say most scientists.
For one thing, they point out, carbon dioxide created from natural sources such as volcanoes still retains a measure of the radioactive element carbon-14, while carbon dioxide released from the burning of fossil fuels does not. In addition, studies performed between the 1950s and the present indicate that levels of this nonradioactive carbon dioxide have risen each year. This evidence, say scientists, can be seen in the decreasing amount of radioactive carbon dioxide captured in tree rings during that time.
Bubbles in ice trapped below the earth’s ice caps have produced samples of prehistoric air in core samples brought to the surface, and researchers say they show that atmospheric carbon dioxide was 25 percent less plentiful 10,000 years ago than it is today. The key: that level remained constant over thousands of years instead of showing the steady rise we see today. Some scientists are certain that the actions of human beings are the cause for this increase.
Balderdash, say critics: most of these CO2 emissions would still take place even if there were no humans on Earth at all, and blaming people for global warming is too simplistic a solution for such a complex problem. They argue that the intricate relationships among all the atmosphere’s elements make the creation of a truly accurate climate change model impossible. They point to a competing study that examined ice core samples and concluded that CO2 levels did fluctuate during the preceding 10,000 years. Besides, they say, CO2 accounts for only 10 percent of the greenhouse gases in the atmosphere; the major culprit is water vapor.
Some scientists theorize that global warming could actually be beneficial, bringing relief to snow-prone areas in the winter and reducing the number of annual deaths due to hypothermia. Warmer weather would also bring longer growing seasons, increasing crop yields, and more carbon dioxide in the atmosphere would make plants more vigorous.
Are you confused yet? So is everyone else, but with 6.6 tons of greenhouse gases being emitted for each man, woman, and child in the United States each year, some say the “better safe than sorry” approach of reduction is the best policy. America is the earth’s second-largest source of CO2 pollution, and the rate is increasing—one reason why Congress established the US Global Change Research Program in 1990.
Creating more bureaucracies is certainly one way to attack the issue, but other ways of reducing carbon dioxide emissions have been proposed. One is carbon sequestration, which the US Department of Energy thinks could be used to cut carbon dioxide emissions by a billion tons a year by 2025 and 4 billion tons by 2050. The method proposes to get rid of carbon dioxide by dumping it into the ocean, which is already the earth’s major carbon dioxide holding area. The seas contain more than 45 trillion tons of carbon, but scientists say there’s room for a lot more.
The process involves pressurizing and chilling carbon dioxide, then pumping it deep into the sea. Sinking to the bottom, it spreads out and thins, eventually dissolving into the seawater. Tests indicate the carbon dioxide dissolves slowly enough to leave sea life unharmed, but fast enough that it doesn’t form thick pools that could smother bottom-dwelling plants and fish. Other scientists say it would be easier and just as effective to pump carbon dioxide back into the ground where it came from, and tests are under way to examine that possibility.
Many scientists say that to better understand why the earth is warming, you have to look at its main source of heat: the Sun. As with any other global warming theory, the effect of the Sun’s influence is still being debated, but many researchers feel that solar variability could be responsible for at least a third of the temperature rise seen in the past century.
But isn’t the Sun’s energy output a constant? Not really. To astronomers, our Sun is known as a variable star, because its production of radiation varies in a cycle that lasts an average of eleven years, a pattern discovered by amateur astronomer Heinrich Schwabe in 1843. That variation is small—only about 0.1 percent—but it’s thought that the fluctuation has been greater over longer time scales, changing by as much as 0.5 percent.
Recently, scientists have discovered statistical links to the Sun’s energy output and the number of sunspots on its face. Examining historical records, they found that in the period between 1640 and 1720, the number of sunspots fell dramatically, and so did the earth’s average temperature, plunging an average of 2°F. The effect was particularly noticeable in Northern Europe, where glaciers advanced southward and winters were especially harsh.
Sunspots are relatively cooler areas in the Sun’s photosphere, so it would seem that fewer sunspots would mean a hotter Sun and hence a warmer atmosphere here on Earth. Once solar-observing satellites were able to examine sunspots closely, however, the mystery was solved: the bright areas called faculae, which accompany sunspots during the solar cycle, are much hotter than sunspots and more than make up for their cooling effect.
Another possible solar effect on climate could be the fluctuation in the UV part of the spectrum, which is much more wildly variable than visible light. During a peak in the Sun’s eleven-year cycle, UV radiation increases by a few percent, compared with the 0.1 percent increase in total radiation. Most of it is blocked by the upper atmosphere, but because all the atmospheric layers are connected, constant UV bombardment can affect the amount of ozone in the stratosphere. That effect eventually propagates down to the surface, so UV radiation could be another component of the climate change riddle.
The Sun also ejects vast amounts of charged particles and magnetic radiation, also thought to have an effect on Earth’s climate. This flood of energy—the solar wind—constantly streams past Earth, flowing around the planet’s magnetic field. During periods of solar maximum output, the Sun’s magnetic field is stretched past the earth, helping to block cosmic rays from entering the atmosphere. But during quieter phases, more cosmic rays leak through.
Some scientists suggest that an increase in cosmic rays can affect the amount of clouds and rain, having a direct effect on the earth’s temperature. It was recently discovered that high levels of cosmic ray activity cause the upper atmosphere to become highly conductive, leading to higher electrical charges in water droplets, causing more rain. The proof, they say, is found in the increased carbon-14 levels caused by cosmic rays that have been recorded in tree rings.
In addition to passing through its cycles, the Sun is also moving through space at around 486,000 miles per hour, dragging the solar system with it. At that speed, it takes the Sun about 226 million years to complete one revolution around the Milky Way Galaxy. The last time the Sun was at the present spot in its galactic orbit, humans didn’t exist yet, and dinosaurs were the dominant species on the planet.
Interesting, but what’s our galactic orbit got to do with global climate change? Well, as the solar system orbits in the galactic plane, the flat disk in which the galaxy’s spiral arms are found, it bobs up and down like a cork. So every thirty million years or so, the entire solar system passes through a thicker layer of interstellar dust, gas, and debris. During the passage, it becomes much more likely that the Sun will encounter large bodies like other stars and planets, and when this happens their gravitational effects can have a powerful influence on the solar system.
As a large body passes near the Oort cloud, which is a gigantic halo of rock and ice fragments that orbits out past Pluto, some of these objects are slowed or sped up by gravitational attraction, either ejecting them from the solar system or causing them to fall inward toward the Sun. As these celestial missiles enter the inner solar system, they pose an increased danger of collision with Earth. Another effect a passage through the Milky Way’s spiral arms might cause is higher-than-normal concentrations of dust falling into the Sun, causing it to burn brighter and hotter, which would increase the amount of solar radiation received by the earth and so increase the average temperature of the atmosphere.
In 1967 another potential source of climate disturbance was discovered when scientists were studying data from satellites looking for Nuclear Test Ban Treaty violations. Instead of radiation from Earth, they found several sources of intense gamma ray bursts coming from outer space. Gamma rays are the most intense form of energy known. Since then, researchers have been unsure of what causes the bursts—called GRBs for short—but increasing evidence indicates they may be the result of supernovas, which are the explosive deaths of massive stars.
When a giant star collapses, it causes an explosion so violent that for a few moments it becomes the brightest object in the universe. The blast creates an intergalactic shock wave that expands outward in all directions like a giant bubble while the star’s interior collapses on itself, often forming a black hole. A new theory states that another, faster jet of material from the dying star moving at nearly the speed of light can overtake that bubble’s outer boundary, causing a second explosion, which generates a GRB.
Although astronomers have located GRBs only in other galaxies, it is thought they were once more common in the Milky Way and could have affected ancient Earth’s climate. Be glad they’re not common today: GRBs can release more energy in ten seconds than the Sun will generate in its entire ten-billion-year lifetime! Scientists think a GRB in our galaxy could have serious consequences for life on Earth.
Put in that perspective, slow global warming doesn’t sound quite so bad. Certainly, much more research is needed to determine whether the changes seen in Earth’s climate during the past few decades are a result of natural processes or if mankind’s recent industrialization is lending a hand. Until then, expect the debate to continue unabated.