Much like Venus the Earth is heating up due to the increase in carbon dioxide. The heating up of the planet contributes to the greenhouse effect. This occurrence contributes to raising the surface temperature about 35 degrees Celsius and is responsible for much of the polar ice caps melting to water. To make matters worst, there is some evidence that carbon dioxide that is currently heating up the surface temperature is still increasing due to the increase of pollutants.(18) The same effect is responsible for making Venus the hottest planet in the solar system. The thick atmosphere on Venus traps the absorbed solar energy and raises its average surface temperature. Earth and Venus have some common traits, such as: they are near each other in the Solar System, and have similar sizes, density, and composition. By studying the greenhouse effect on Venus, we can increase our knowledge and understanding so that we may prevent a runaway greenhouse effect on Earth.(19)
Sunlight that comes to the surface of the Earth is mostly in the visible part of the spectrum. The reflection of light from the surface tends to produce light of longer wavelength called infrared radiation (IR). Infrared radiation actually produced by cool surface radiation is radiated from a hot surface like a hot piece of metal. The molecule structures of certain gases like carbon dioxide, water vapor and many others have the property that they are essentially transparent to visible light but absorb IR radiation very strongly. These compounds are called greenhouse gases. They are called greenhouse gases because when they are present in a planetary atmosphere they absorb the scattered IR radiation and raise the temperature of the atmosphere by trapping solar energy.(20)
Most planets have some type of greenhouse gases on it except for Mercury which has no atmosphere. The greenhouse effect is responsible for planets being warmer than they would be otherwise. The greenhouse effect alone does not account for the conditions that we find on Venus, but under certain conditions it is believed the greenhouse effect became unstable. For example, the Earth has enormous amounts of two greenhouse gases: water vapor and carbon dioxide. However, most of the water and carbon dioxide are not in the Earth's atmosphere. The water is mostly in the oceans, and the carbon dioxide is mostly bound chemically in rocks made from compounds that chemists call carbonates, such as, limestone.(21)
If we increased the effectiveness of greenhouse heating of the Earth's atmosphere, by increasing the amount of solar radiation falling on it, or by increasing the concentration of greenhouse gases in the atmosphere by burning fossil fuels to produce water vapor and carbon dioxide (by- products of burning), then we would expect the temperature to rise in the atmosphere assuming no other effects intervened. This would be a greenhouse effect. In real life the atmosphere is complicated to control.(22)
Earth would have a
greenhouse effect if the rising temperature approached the boiling point of water, because then the oceans would begin to convert to water vapor, the water vapor would increase the effectiveness of heat trapping and accelerate the greenhouse effect, which would cause the temperature to rise further, thus causing the oceans to evaporate faster, etc. This is a runaway effect because it is a positive feedback loop. However, once the oceans are gone, the atmosphere would finally stabilize at a much higher temperature and at much higher density because all the water would now be in the atmosphere.(23)
This scenario can be taken further. Suppose the above runaway raised the temperature so high that chemical reactions called sublimation begin to occur. This would drive the carbon dioxide from the rocks into the atmosphere a few hundred degrees Celsius. Then another runaway would occur as the carbon dioxide feeding into the atmosphere would accelerate the heating, which would accelerate the transfer of carbon dioxide from the rocks to the atmosphere. It is easy to see the devastation in this scenario.(24) The atmosphere would stabilize at a still higher temperature and pressure after all the carbon dioxide had been driven from the rocks.
In fact, it is believed that if this sequence were to take place on the Earth, the resulting temperature and pressure of the atmosphere left behind would not be very different from that for present-day Venus. Earth's atmospheric temperature would be hundreds of degrees Celsius and the pressure would be maybe 100 times greater than it is today. (25)
In the case of Venus, it is believed that the initial solar heating kept oceans from forming, or kept them from staying around if they did form, and the subsequent lack of rainfall and failure of plant life to evolve kept the carbon dioxide in the atmosphere rather than binding it in the rocks as is the case for
the Earth; causing Venus to have an environmental disaster for an atmosphere.(26)
The scenario of the runaway greenhouse effect on Venus should make us extremely concerned about processes such as burning of fossil fuels in large volumes that might have the potential to trigger a runaway greenhouse effect and produce on the Earth atmospheric conditions such as those found on Venus.
Since the Sun is by far the largest supplier of energy to the Earth's surface, any change in the radiative output of the Sun also affects the energy balance of the Earth's surface and atmosphere, so that at some level it influences our climate, too. But how strongly does the Sun vary and to what extent does it influence the Earth's climate? One of the most important ways to find a definitive answer to the question of the solar effects on global warming is to determine its weight relative to that of the man-made greenhouse gases.(27) Most scientist think that greenhouse gases from fossil fuels have contributed to the warming of the planet in past decades, but do not rule out that a brighter Sun is also responsible for rising temperatures. To determine the Sun's role in global warming, magnetic zones or sunspots on the Sun's surface are measured for energy output of the sun. More evidence will need to be sought after before it can be determined whether greenhouse gases causes global warming alone or does the Sun also has an effect on global warming.