Early Human Response To Climate Change

Originating in Africa with a body adapted to warm weather, humans thrived in the moderate climate of antiquity. Inventing agriculture at the end of the most recent Ice Age, humans settled in the warm latitudes that sustained the growth of crops. At the margins, however, the climate was inhospitable. The Near East had long been arid. Around 4,000 years ago the Akkadians relied on rainfall, scant as it was, to irrigate their crops. When the rains failed, their civilization collapsed. Drought likewise extinguished the Mayan civilization of southern Mexico and Guatemala 1,200 years ago. In Europe, however, the Medieval Warm Period between 1,000 and 1,300 c.E. rewarded peasants with bountiful crops. They seldom went hungry, and landlords grew rich on the proportion of the harvest that they commandeered from the land. The favorable climate allowed Europeans to finance the crusades and the building of cathedrals.

Yet after 1300, the climate turned against Europeans. In only a generation, summers went from warm to cold and wet, and crops rotted in the fields. Having enjoyed a surplus of food, peasants were now on the verge of starvation. They clashed with landlords over who had a right to what little harvest there was. Malnutrition left Europeans vulnerable to disease, and the Black Death killed between one third and half the population. Climate had conspired with disease to inflict misery on a scale that is difficult to imagine. The cold climate intensified between 1645 and 1715

when the Sun, shedding one percent less sunlight than it does today, chilled Earth, cooling it 2 degrees F (1 degree C) . The diminution of sunlight corresponded with the low number of sunspots during these years. Sunspots are a measure of how much heat the Sun radiates into space and indicate, in this instance, that a small diminution in the sun's activity suffices to cool Earth. The eruption of Mount Laki, a volcano on Iceland, in 1783 spread volcanic ash and debris across the Northern Hemisphere, blocking out sunlight and cooling Earth. The eruption of Mount Tambora in Indonesia had a similar effect. By 1816, temperature had fallen 7 degrees F (3.8 degrees C) in New England and 5 degrees F (2.7 degrees C) in Europe. History records 1816 as the year that had no summer.

Although temperatures, with some fluctuation, have declined during the past 55 million years, they are beginning to rise again because of the greenhouse effect. Since 1750, the amount of methane, a greenhouse gas in the atmosphere, has risen 2.5 times. Fortunately, methane does not persist in the atmosphere, but breaks down in a few years. More worrisome is the amount of CO2, which since 1750 has risen 31 percent. Unlike methane, CO2 does not deteriorate, and has the potential to remain in the atmosphere for centuries. Since 1900, temperatures have increased 1.3 degrees F (0.7 degrees C) and the sea level has risen 6 in. (15 cm.) from the melting of glaciers in Greenland and Antarctica. Since 1973, the polar icecaps have shrunk six percent. The snow is melting from Mount Kilimanjaro in Africa and the Himalayan Mountains in Asia. Adding to the Greenhouse Effect is an increase in the number of sunspots since 1985. The increase in temperatures may intensify the climate, causing hurricanes in the Caribbean and Gulf Coast, and droughts in Africa and North America.

Curiously, temperatures and the amount of CO2 in the atmosphere were higher 130,000 years ago than they are today; yet, the earlier warm climate was followed by an ice age. Therefore, scientists may not be able to predict if the current temperatures will spiral upward or will end in yet another ice age. Unsure of the future, humans are increasingly aware that their activity affects the climate. The burning of fossil fuels at a prodigious rate pollutes the atmosphere with more CO2, threatening to raise temperatures still further. In the developed world, progressives talk about renewable energy, but despite their rhetoric, countries continue to pump CO2 into an already crowded atmosphere. In Central and South America, people are chopping down the rainforest, removing the trees and plants that would have consumed some fraction of the CO2. Earth, and with it the climate, may be in crisis.

SEE ALSO: Climate; Climatic Data, Historical Records; Ice Ages; Greenhouse Effect.

BIBLIOGRAPHY. Lawrence Frakes, Climate Throughout Geologic Time (Elsevier/North-Holland, 1979); Thomas Grae-del, Atmosphere, Climate and Change (W.H. Freeman, 1995); Wilfrid Kendrew, The Climates of the Continents (Clarendon Press, 1961); Sharon Spray, Global Climate Change (Rowman & Littlefield, 2002).

Christopher Cumo Independent Scholar

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