Nerdy Science Blog

Global warming, or climate change, currently generates a great deal of discussion among scientists, the media and the general public. Environmentalists blame human activity for what is perceived as a slow warming of Earth’s atmosphere, creating the possibility for many impending calamities. Critics of this feel that global warming, if it is occurring at all, is a natural process to which humans are contributing very little. It is important to remember during this sometimes heated debate that Earth’s climate has never been static and that the modern climate we are experiencing is not a permanent development. Indeed it may not even be the “normal” climate for our planet.

Earth is, by most scientific estimates, around 4.5 billion years years old. We have only been scientifically measuring temperature and other weather data since the late 1800’s. The United States Army began collecting weather records at Fort Brown near Brownsville, Texas in 1850.

It wasn’t until 1878 that President Ulysses S. Grant signed a Congressional resolution into law requiring the Secretary of War to collect the weather data generated by the various military posts, States and territories. By this time weather records were fairly complete, so from 1878 on climatologists can use the data for climate study purposes. So we only have reliably accurate weather records for about 125 years of our planets 4.5 billion years of existence.

Climatologists can make guesses about the climate of Earth’s past using various other sources, including tree rings, ice core samples at both the Artic and Anartic, and from ocean sediment studies. Past temperature trends, atmospheric makeup and rainfall can be inferred from these and other sources. And all evidence points to the fact that the Earth’s climate is always changing.
Climate change has occurred within the historical record. Both the Medieval Warm Period and the Little Ice Age have occurred within recorded times.

Most scientists feel that the Medieval Warm Period began around 800 AD and lasted until around 1300 AD. There is disagreement about whether the phenomenon was global, or localized to the northern hemisphere. Nonetheless, it was a period of warming. During this period, Icelanders colonized portions of Greenland. Colonists from Iceland arrived around 984 AD and persisted for just over 450 years. They settled primarily on the southwestern tip of Greenland where they found the land above the fjords lush and green. The settlers survived by farming, hunting and trapping. Livestock included sheep, cattle and goats.

There were two main settlements on Greenland during the Medieval Warm Period, and one minor one. The Eastern Settlement was the larger of the two, totaling around 4000 people when it was at its peak, comprising approximately 300 to 400 farms. The Western Settlement had possibly 1000 inhabitants. There was also a Middle Settlement of around 20 farms along the coast. The livestock grazed on the native Arctic heath which covered the ground. The settlers ate cheese and milk produced by the animals, and hunted caribou, seals, and fish. The growing season was too short for any grain crops, so they probably had no bread or beer.

During this period Iceland was more hospitable than it today. Arctic sea ice retreated, grape culture was possible in Great Britain and the tree line in the Alps was higher than it is currently.

Wide disagreement among scientists places the beginning of the Little Ice Age anywhere from 1250 AD to 1650 AD. Most climatologists agree that it ended by the middle of the eighteenth century. Originally it was thought that was a global event, but research has raised questions about that theory. But there is little doubt that there was cooling in the Northern Hemisphere that lasted from 100 to 500 years. Bitter cold winters were brought on by this Ice Age, and glaciers in North America, Greenland, and Europe advanced. Harbors on Iceland were closed due to sea ice extending great distances in every direction. New York Harbor froze, allowing pedestrian traffic from Manhattan to Staten Island during the winter.

The cold also affected the food supply. In North America, Indian tribes which were traditional enemies allied themselves to share food resources. In Europe, farming practices were altered to account for the colder weather. The Viking colonies of Greenland starved out during this period. Traditional orange growing areas in China, which had grown this citrus crop for centuries, had to abandon the trees. England’s growing season was shortened by one to two months. Millions of people died in France and neighboring countries when the wheat crop failed in 1683. Norwegian farms in the higher mountain elevations had to be abandoned. The hay crop in many countries was much reduced, and cattle had to be fed pine needles or slaughtered. It is thought by many experts that the Stradivarius musical instruments produced during that period owed their superior sound quality to the better quality of the hardwood produced by slower growing trees during the Little Ice Age.

By 1850, the Little Ice Age ended and Earth entered a gradual warming phase. It is possible that the current warming trend is simply an extension of the trend started then. It is thought by some scientists that the cooling was caused by a combination of increased volcanic activity and decreased solar activity. No one knows for sure.

Ice Ages are periods of global cooling intense enough to cause glacial ice to advance in both the Northern and Southern hemispheres. They occur at approximately 100,000 year intervals, the last one ending about 10,000 years ago. Some experts feel that we are still in an ice age, as glacial ice still envelopes Greenland, the Arctic, and most of the Antarctic. The most severe ice age occurred just before the age of dinosaurs. During that one it is thought that the glacial ice cover extended to the equator.

Historically, interglacial periods are warm periods between the much longer ice ages. Most climatologists believe these last about 12,000 years. Since the one we are in has lasted around 10,000 years already, there are some who feel that this interglacial may end at some time in the near future. By no means is this a universal belief among scientists. Some believe that it could last as long as 26,000 years.

What causes these climatic variations? Experts do not agree on the cause. Some think they are caused by regular variations in the earth’s orbit around the sun. Others feel it is by variations in sunspot activity. Possibly it is some combination of the two. Atmospheric carbon dioxide also plays a role in the process. Too much, and the earth warms. Too little and the earth cools. There is some disagreement about this too, as some scientists assert that cold periods coincide with higher carbon dioxide levels.

In summary, the earth’s climate has never been static. It has changed over the ages, sometimes rather dramatically. It fluctuates back and forth between times of extreme cold when glaciers blanket a good deal of the earth’s surface, to warm periods in which glaciers retreat to well within the Arctic Circle. Scientists are in disagreement about the causes of this climate variation, though sun spot activity and changes in earth’s orbit seem to be the major causes. Other factors seem to occur, such as comet and other impacts from meteors and asteroids. Whether the earth is indeed warming currently is also open to debate. And if it is, there is some thought that possibly it is due to an already occurring trend which began at the end of the last ice age. About the only thing that can be deduced accurately is that scientists, though they know a lot, still are guessing about a great many things.

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