What Causes Climate Change (Besides Us)?

For years now, scientists have been warning us about the dangers of climate change, although they can’t seem to agree on which direction that change is going. Human activity is generally blamed for causing the problem, although other influences such as bovine flatulence have also been cited as contributing factors. But are we and our livestock really behind the chaotic weather conditions much of the world is currently experiencing?

Since humans have only been numerous enough, and technologically advanced enough, to have an effect on climate in the last 11,000 years or so, it seems logical that other factors must have been at work to create climate change in the previous millions of years.

Modern research has shown that there are other natural influences at work over which people have little or no control. And surprisingly, our current climate problems are somewhat predictable. Many scientists have come to believe that there are climate cycles inside climate cycles, some long and some unbelievably short. The climate patterns the scientists have analyzed seem to generally follow those cycles.

Cycles Within Cycles

Many scientists have come to believe that there are climate cycles inside climate cycles, some long and some unbelievably short. The climate patterns the scientists have analyzed seem to generally follow those cycles.

Beginning in 1912, engineer Milutin Milankovitch conducted a 30-year long study which resulted in what is now known as Milankovitch’s Orbital Theory. His calculations indicated that there were at least two main factors affecting the growth and retreat of the polar ice caps. One was based on the fact that the earth’s orbit around the sun varies from nearly circular to oval in shape. When earth’s orbit is more circular, weather patterns become less violent and more predictable. As the planet moves into its oval-shaped orbit cycle, weather extremes become more profound. This change from circular to elliptical orbit patterns takes place about every 95,800 years.

Another factor influencing global climate is the earth’s tilt. The planet’s north-south axis actually is somewhat tilted in relation to the sun. Regions more exposed to the sun are warmer, those tilted away are cooler. This change in the earth’s tilt is also predictable, ranging from 21.39 to 24.36 degrees and back every 41,000 years. As the angle increases, earth experiences hotter summers and colder winters. Currently the tilt is decreasing by about half a second of a degree per year, changing the latitudes of the Tropics of Cancer and Capricorn and moving the tropical boundaries to the south.

The earth also wobbles on its axis of rotation in a process known as the precession of the equinoxes. This 21,700-year cycle relates to the point at which the northern hemisphere is directed towards the sun. When the planet is relatively close to the sun, winters are short and warm. But when earth is farther away from the sun, winters become longer and colder.

There is yet another oscillation which occurs about every 1,470 years and happened at least 25 times during the last ice age. These are known as the Dansgaard-Oeschger (D/O) oscillations and are characterized by rapid warming episodes followed by a longer period of slow cooling. They may be connected to changes in the North Atlantic and may be the result of melting ice sheets which release great quantities of fresh water into the ocean.

The Sun

The sun is another factor which can, and has, affected temperatures on Earth. It appears to be hotter at times, then becomes cooler for a time before it warms up again. The sun’s heat output has been increasing for about the last 130 years. The mechanism behind this heating and cooling cycle is not yet well understood, but ongoing studies of both the phenomenon and its effects on the earth may soon shed more light on the sun’s effect on climate change.

Volcanoes

Some volcanoes have had profound, though generally short term, effects on global weather. When Mount Tambora erupted in 1815 in Southeast Asia, ash clouds dimmed the sun over much of the world and caused the “Year Without a Summer” in 1816. The famous explosion of Krakatoa in 1883 was even smaller than the Mount Tambora event, but still caused short-term changes in the world’s weather patterns.

The greatest volcanic event of the last 23 million years was the gigantic eruption of Mount Toba on the island of Sumatra about 73,500 years ago. This super-eruption is said by some to have nearly wiped out humanity. Massive amounts of sulphur were thrown into the air, dimming the sun and dropping temperatures to some of the lowest recorded during the last ice age. The effects of this massive eruption are believed to have lasted as long as 2,000 years. Some experts now believe that the great supervolcano underlying North America’s Yellowstone National Park poses as great a threat to the world as the spectacular Mount Toba eruption did nearly 75,000 years ago.

Conclusion

Earth is currently enjoying a warm period between ice ages. The last great cold spell, when temperatures ranged from about 10 to 12 degrees Fahrenheit (6 to 7 degrees Celsius) cooler than today, began to end about 18,000 years ago. But the warming trend was not uniform and tended to fluctuate, sometimes violently, over about 10,000 years. One recent example of this was the so-called Little Ice Age of the 15th through the 18th centuries, which followed a period of unusually wet and warm weather known as the Medieval Warm Period.

Many researchers believe that the combined effects of the cyclic orbital changes, along with Earth’s own axial tilt and wobble, cause the planet to swing back and forth from glacial to interglacial roughly every 100,000 years. It may be that mankind’s effect on the planet could forestall or mitigate the effects of the next ice age, but it is unlikely to stop it.

How soon might we expect the beginning of the next ice age? Usually the interglacial periods only last about 10,000 years, and Earth has enjoyed relatively mild temperatures for about that long. If the cyclic history of climate change is any indication, Earth may soon begin its slow and violent descent into a new cold spell, possibly over the next several hundred years.

Selected References:

Earth Under Fire: How Global Warming is Changing the World, 2007, Gary Braasch, University of California Press, Berkeley, California

Discovery! Unearthing the New Treasures of Archaeology, Brian M. Fagan, ed., 2007, Thames & Hudson Ltd., London

Europe Between the Oceans, 9000 BC to AD 1000, 2008, Barry Cunliffe, Yale University Press, New Haven, CT

Ice, Mud and Blood, 2008, Chris Turney, Macmillan, 175 Fifth Ave., New York, N. Y. 10010


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