Is global warming a natural cycle of the earth's revolution?
There have been what is known as the Ice Ages when the much of the earth was covered by glaciers and the average temperature of the earth was much cooler than the present.
There have been periods of earth's history when the average temperature and humidity levels were much higher than they are today. The fossil coal beds are indications of a much warmer climate.
The known history of Greenland proves that there are natural cycles of warming and cooling. The Vikings were able to cultivate grapes and wheat in Greenland during their occupation of Greenland around 1200 to 1400 AD. Then the climate cooled and the Vikings were forced to abandon their settlements in Greenland.
During World War II American fighter planes short of fuel landed on glaciers. Over the next forty years the climate was colder and the planes were covered by ice. Recently the ice melted and the planes were exposed sitting on the original glaciers they landed on in World War II.
The present global warming trend could be due to human activities such as burning fossil fuels as well as the natural cycles of warming and cooling experienced by the earth.