Changes

According to geologists, the Earth has experience numerous [[ice age]]s during which the temperature dropped so far that [[glacier]]s could cover [[North America]] and [[Europe]].  

According to geologists, the Earth has experience numerous [[ice age]]s during which the temperature dropped so far that [[glacier]]s could cover [[North America]] and [[Europe]].  

There is a close correlation between the average temperature of the Earth's atmosphere and the amount of [[carbon dioxide]] in the atmosphere. During warm periods, the carbon dioxide level increases, and during cool periods it decreases.<ref>[http://www.nature.com/nature/journal/v399/n6735/abs/399429a0.html Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core]</ref> Today the carbon dioxid concentration is 380 ppm. The pre-industrial level was 280 ppm.  

There is a close correlation between the average temperature of the Earth's atmosphere and the amount of [[carbon dioxide]] in the atmosphere. During warm periods, the carbon dioxide level increases, and during cool periods it decreases.<ref>[http://www.nature.com/nature/journal/v399/n6735/abs/399429a0.html Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core]</ref> Today the carbon dioxid concentration is 380 ppm. The pre-industrial level was 280 ppm. The current carbon dioxide concentration ist the highest since at least 650,000 years.  

==Politics of global warming==

==Politics of global warming==