Many people perceive greenhouse gases negatively because of their connection to global warming. Yet if it weren't for the greenhouse effect, life on Earth might not be possible. The greenhouse effect is a natural phenomenon whereby greenhouse gases trap heat that would otherwise be released into space. According to the Pew Center on Climate Change, this trapped heat raises the temperature of Earth's surface by about 60 degrees Fahrenheit.
Greenhouse gases can become problematic when they rise to a level that raises the Earth's temperature too much. Some scientists say this has led to global warming and climate change, resulting in rising sea levels, melting glaciers and endangered species.
The most important greenhouse gases include water vapor, carbon dioxide, methane, ozone and nitrous oxide. Of these, water vapor is the most abundant. Like many of the other greenhouse gases, water vapor is a naturally occurring gas and exists as a natural result of the water cycle.
The amount of water vapor in the atmosphere is part of a "feedback loop" related to the Earth's temperature. The cycle is fairly simple: As the temperature rises, more water evaporates. Because warmer air is able to hold more water, this leads to more water vapor in the atmosphere. This higher level of water vapor then serves to trap even more heat in the atmosphere, leading to further increases in temperature. This cycle is called a positive feedback loop.
As the Pew Center on Climate Change states, higher levels of water vapor can be traced to the Earth's rising temperature, which some scientists say is linked to rising carbon dioxide concentrations.
Although water vapor is the most prevalent greenhouse gas, it is not primarily responsible for global warming because of its short "residence time" -- the fact that concentrations of it do not exist long enough to elevate the global temperature. Large amounts of it would rain out within a matter of days, while it takes decades for heat to build up in the atmosphere. It is the more persistent greenhouse gases, such as carbon dioxide, methane and ozone, which some scientists say drive global warming: Levels of water vapor simply rise as a response to their heat-trapping effects. That being said, water vapor's existence does serve to compound the warming.
Despite all the research that has been done surrounding climate change, the feedback loop that water vapor is a part of is still not entirely understood. Despite current observations, for instance, there's also the possibility that increased water vapor could lead to greater cloud formation down the road, thus reflecting solar radiation and leading to less global warming. More observation and research into the complex feedback loop is being done to fully comprehend the effects of water vapor and its interactions with the other greenhouse gases.