What is the
basis for the predictions concerning global warming? There are several
gases in the air, collectively called greenhouse gases, that trap the
infrared radiation emitted from the Earth. Although these gases make up a
small percentage of our atmosphere, they significantly affect the amount
of infrared light energy leaving the earth. Therefore, they disrupt the
heat budget and are a cause of global warming.
Since the start of the industrial revolution, human activities have caused a steady increase in the concentration of some greenhouse gases to unprecedented levels in our Earth's recent history. The most abundant of these is carbon dioxide (CO2). It accounts for about 64% of the total absorption of infrared energy by greenhouse gases. The level of atmospheric CO2 increased by about 11% between 1958 and 1988. Currently, the level is rising at about 0.4% annually because we are adding more carbon to the atmosphere than is being removed....by about 5 gigatonnes annually. (What is a gigatonne? One gigatonne = 1 x 1012 kg.) Almost all of this is the result of burning of fossil fuels and deforestation, which are both manmade sources. The other 36% of the greenhouse effect is due primarily to: methane gas, nitrogen oxides, ozone and chlorofluorocarbons (CFCs). To study these greenhouse gases or the carbon cycle in more detail, take a look at our advanced research page.
Water vapor (or
a cloud, in other words) is a greenhouse gas that has not been included in
the above percentages, because its total effect on global climate change
is not fully understood. For example, when water vapor's physical state
changes (water, snow, ice), its effect on global warming changes. However,
we do know that water vapor's total effect on global warming is greater
than CO2's.
The ARM Program is designed to better understand how water vapor affects climate change. The data gathered from our three field research sites is providing us with some important information about this greenhouse gas and its impact on global warming.