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Exploring Climate Events and Human Development
The Past 100 Years: The 20th Century's Human Climate Conundrum
Current Esimate of Global Population

The 20th Century has been like no other. With human population jumping from 1.6 to 6 billion between 1900 and 2000, there have been more people vulnerable to climate change than ever before. Moreover, during this same period, carbon dioxide concentrations in the atmosphere have risen from 290 parts per million (ppm) to 369 ppm, with strong Image showing 400,000 year record of CO2 levelsevidence pointing to the burning of fossil fuels as a primary cause of these increases. Many climate researchers and policy makers are concerned that increased in population and rising standards of living will lead to ever higher levels of carbon dioxide and other greenhouse gases. See the Intergovernmental Panel on Climate Change (IPCC), Etheridge, et. al., 1998 and U.S. EPA Global Warming.

During the 20th Century there were two world wars, numerous hurricanes and typhoons, influenza breakouts, droughts and famines... and at virtually every step of the way climate played some role in the events.

There has also been increased cloud cover, particularly in the Northern Hemisphere during the past century (Groisman, 1999). While water vapor is the most abundant greenhouse gas, low clouds also shade and cool the surface. Currently the role that water vapor and clouds play in warming or cooling the Earth's climate system is being investigated by scientists.

The 20th century has experienced catastrophic climate events. The worst tropical storm of the 20th century occurred in Bangladesh in November 1970 where 300,000-500,000 people were killed due to winds coupled with a storm surge.

The most destructive climate-related event was likely the Yangtze River Flood of 1931 that impacted over 51 million people (1/4 of China’s population), including 3.7 million people who perished due to disease, starvation or drowning. The flood was preceded by a prolonged drought in China during the 1928-1930 period.

Image showing how drought of 1950s compares with prior droughtsDroughts have also caused severe problems in the United States during the 20th Century. The "Dust Bowl" in the 1930s hit the midwest particularly hard. Another drought in the 1950s impacted the Southwest, but compared with long-term paleo records, neither of these droughts were as severe or long-lasting as other droughts in prior centuries, as the graph to the right shows. (See Paleo Perspective: North American Drought) for more on the human impact on climate.)

Have swelling populations and human activities such as the burning of fossil fuels lead to warmer temperatures and global warming? Research shows that global temperatures have in fact risen by .6 degrees Celsius over the past 100 years and the National Academy of Sciences indicate that the increase is due in large part to human activity. (See Whitehouse briefing from June 11, 2001.) According Mann et. Al, 1999, the 20th century warming counters a millennial-scale cooling trend which is consistent with long-term astronomical forcing. Also see Paleo Perspective Global Warming for more on human impact on climate.

Click here to view Putting the 20th Century in Perspective

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