by Larik Sonfar

Created on: May 23, 2008

Ruddiman, William, F. 2005. How did Humans First Alter Global Climate.
Scientific America, March, 2005.

Summary

Both scientific consensus and public perception accept that global warming, or the rise in levels of heat trapping gasses such as carbon dioxide and methane, began in the industrial era with such inventions as coal burning factories and power plants. However, new evidence suggests that carbon dioxide and methane concentrations began rising unnaturally far before the world began to industrialize. Around 8000 years ago, CO2 concentrations began to rise even as natural trends suggested they should drop. Around 3000 years ago, methane concentrations also began to rise. Consequently, temperatures in North America and Europe today are three to four degrees Celsius higher than they ought to be. Other evidence suggests that this rise in temperatures helped to avert an ice age in parts of the Northern Hemisphere. This strange discovery, not in accordance with the general ideas behind global warming, led to this investigation.

Having found strange occurrences in nature which could not be explained with accepted scientific ideas, the author of this experiment established the key causal question for this investigation as: [What caused global warming thousands of years ago?]

The author hypothesized that global warming thousands of years ago was caused by humans and the beginning of agriculture, which included deforestation and crop irrigation.

In order to test these hypotheses, the author of this experiment set out to collect and examine all the evidence collected by various scientists regarding global warming, CO2 and methane concentrations in the atmosphere, and other related trends. The author first examined records of the Vostok ice core in order to look for traces of methane concentrations thousands of years ago. He then compared these results with expected trends from orbital cycles. Eventually, this led to the results of this experiment.

The author observed that although orbital cycles and previous trends suggested that methane reached its peak of 700 parts per billion 11,000 years ago. Afterwards, the concentration followed trends and began to decline. It should have then fallen to 450 parts per billion, but the trend reversed direction around 5000 years ago and rose unnaturally back up to almost 700 parts per billion. This was 250 parts per billion higher than natural trends suggested it should have been at that time. Carbon dioxide concentrations also started

• 1
• 2
• 3
• Next Page >>