any doubt about the global warming ?

global warming temperature carbon dioxide level Over the past 425,000 years, cool periods have coincided with times when the CO2 concentration in the atmosphere was lower. When there is less CO2 in the atmosphere, the greenhouse effect is reduced and the world cools.
The blue and red line indicates the variation in average global temperature compared with the 1961–1990 average. The green line shows the concentration of CO2 in the atmosphere. (Pay close attention to the right-hand edge of the graph.)
This graph shows four eras when the world was cooler than it is today. These are separated by brief warm periods, like the one we are now in.
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There is much discussion about the global warming. Many still have doubts about if it is a real threat, even if it will actually happen.
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Observing the global atmosphere temperature along the past one sees that it presents a sort of cyblic behavior approximately each hundred thousand years. According to this cyclic behavior we are in the end of a "hot time", and this is the reason of the belief that, instead of a global warming, we are about to enter a new glacial era.
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Paying attention to the historic record of the carbon dioxide concentration in the atmosphere turns evident the close relation between it and the temperature of the atmosphere.
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Looking closely to the very right side of the graphic above it is possible to see that the carbon dioxide concentration rose dramatically. This leads us to infer that the global temperature will be pushed up.
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It follows a plot of the last hundred and thirty years increase in the carbon dioxide concentration.
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Sources:
Woods Hole Research Center
UNEP - United Nations Environment Programme