thermal energy
Thermal energy can be trapped in Earths atmosphere by gases such as CO2, water vapor, methane, and chlorofluorocarbons before it can be radiated into spacelike the effect of a greenhouse. It is not yet clear how large an increase in the temperature of Earths surface can be attributed to this phenomenon. Venus is an example of a planet that has a runaway greenhouse effect. The atmosphere of Venus is about 95 times denser than that of Earth and contains about 95% CO2. Because Venus is closer to the sun, it also receives more solar radiation than Earth does. The result of increased solar radiation and high CO2 levels is an average surface temperature of about 450C, which is hot enough to melt lead. Data such as those in Figure 5.22 "Changes in Atmospheric CO" indicate that atmospheric levels of greenhouse gases have increased dramatically over the past 100 years, and it seems clear that the heavy use of fossil fuels by industry is largely responsible. It is not clear, however, how large an increase in temperature global warming may result from a continued increase in the levels of these gases. Estimates of the effects of doubling the preindustrial levels of CO2 range from a 0C to a 4.5C increase in the average temperature of Earths surface, which is currently about.