global warming
...ect because as incoming solar radiation strikes the surface, the surface gives off infrared radiation, or heat, that the gases trap and keep near ground level. The effect is comparable to the way in which a greenhouse traps heat, hence the term. Environmental scientists are concerned that changes in the variable contents of the atmosphere--particularly changes caused by human activities--could cause the Earth's surface to warm up to a dangerous degree. Since 1850 there has been a mean rise in global temperature of approximately 1° C (approximately 1.8° F). Even a limited rise in average surface temperature might lead to at least partial melting of the polar icecaps and hence a major rise in sea level, along with other severe environmental disturbances. An example of a runaway greenhouse effect is Earth's near-twin planetary neighbor Venus. Because of Venus's thick CO2 atmosphere, the planet's cloud-covered surface is hot enough to melt lead. Water vapor is an important "greenhouse" gas. It is a major reason why humid regions experience less cooling at night than do dry regions,. Ho...