Pre-industrial Humans and Greenhouse Gases
The introduction of greenhouse gases into the atmosphere as a result of human activity is not just a relatively recent effect of the Industrial Revolution. Humans have been releasing carbon dioxide and methane from farming and herding activities for millennia, and analysis of Antarctic ice cores has shown changes in greenhouse gas patterns during interglacial periods corresponding to changes in human activities. Prior to the last ice age, the amounts of carbon dioxide and methane in the air during these times decreased along with the levels of summer sunshine, which varied due to cyclical changes in the orbit of the Earth. This pattern was discovered to have changed after the last glacial period, at its height about 12,000 years ago. Even though summer sunshine has been decreasing, carbon dioxide in the atmosphere began to increase 8,000 years ago, with methane levels starting to rise 5,000 years ago.
With possible natural causes for this change in pattern eliminated, it has been suggested by William Ruddiman, climate scientist at the University of Virginia at Charlottesville, that early farming practices in Europe, China, and India, with the clearing of forests for agriculture, explain the increased amounts of carbon dioxide in the atmosphere, and livestock herding accounts for the rise in methane. For example, by the time of the Roman era in Britain, large areas of forest had already been cleared, illustrating that deforestation has been occurring for far longer than just the last two centuries.
Ruddiman has estimated that prior to 1700, farming and herding by pre-industrial humans released into the atmosphere about 40 parts per million of carbon dioxide and 250 parts per billion of methane, producing almost .8 C of global warming, the equivalent to the amount humans have contributed in the last 300 years. He has also suggested that this rise in greenhouse gas levels in the atmosphere warmed the climate enough to avert a new ice age. Scientists at the University of Wisconsin-Madison, using climatic computer models, suggest this rise in greenhouse gases would have raised the world temperature 2 C above what it would have been without human activity .
Other scientists point out that other gases interact with atmospheric carbon dioxide and methane, therefore, changes in the levels of these gases could account for increases in the greenhouse gases. Others have argued that if relatively few humans, using pre-industrial technologies, could cause such a large impact on the Earth’s climate, the rapid increase in the concentrations of greenhouse gases seen in modern times, over such a comparatively short period, is cause for concern.
This entry was posted on Tuesday, August 14th, 2007 at 6:27 am and is filed under Public Relations, Space Agency News. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
