Greenhouse Gases and Greenhouse Effect
What are Greenhouse gases? When the sun’s rays hit the Earth, approximately 70 percent of the energy stays on the planet, absorbed by land, oceans, plants and other things. But even the 70% radiation that gets absorbed, radiate it back eventually — some of which escapes into space and the rest absorbed by atmospheric gases such as carbon dioxide, methane gas and water vapor. This absorbed heat keeps the planet warmer than it is in outer space, and makes life possible.
Carbon-dioxide, methane, nitrous oxide, etc, are called greenhouse gases as they turn the globe into a green house. Without these natural greenhouse gases like carbon dioxide, methane, and nitrous oxide in the atmosphere, the world’s average surface temperature would be a chilly -18 degrees Celsius. Thanks to the greenhouse effect, however, we enjoy an average temperature of 14 degrees.
Understanding the Carbon Cycle
Forests, soils, oceans and the atmosphere all store carbon and this carbon moves between them in a continuous cycle. Many of our activities have contributed to the rise in the levels of greenhouse gases. Burning fossil fuels spews greenhouse gases at a life-threatening rate. Tests have shown that the level of carbon dioxide in the atmosphere is rising significantly.
Burning of Fossil Fuels and Effects of Deforestation
Coal, oil and natural gas are fossil fuels. When these are burnt, the fossil carbon stores are released into atmosphere and results in increasing the greenhouse gas concentrations to levels higher by 30 per cent than at the beginning of the industrial revolution.
Forests lock up atmospheric carbon in their foliage via photosynthesis and temporarily sink the carbon that fossil fuel burning releases into the atmosphere. When forests are burned, degraded, or cleared, the opposite effect occurs: large amounts of carbon dioxide along with other greenhouse gases (nitrous oxide, methane, and other nitrogen oxides). are released into the atmosphere.
Methane, the second most important greenhouse gas after carbon dioxide and the primary component of natural gas, is virtually omnipresent. The UN Panel on Climate Change reports that methane levels have increased by about 150 percent since 1750. This gas emanates from the Earth’s mantle through volcanoes and from the guts of millions of livestock, rises from decaying matter, wetlands, marshes, landfill sites and coal mines. Methane is also released by the burning of fossil fuels. The good news is that methane disappears faster from the atmosphere than CO2. After about seven years, half of all methane emissions have transformed into water and carbon dioxide.
Since the last decade, methane emissions have somehow stabilized and even decreased slightly, while carbon dioxide levels have increased rapidly. This is because many wetlands are being reclaimed for agricultural use and methane is often recovered from landfills.
Nitrous oxide: increased Use of Fertilizers and Pesticides
Farmers around the globe use more than 70 million tons of nitrogen fertilizers annually. It is estimated that some 3 to 5 percent of this nitrogen is converted directly into nitrous oxide. Nitrogen is the chemical basis for proteins and DNA. Tiny bacteria in the soil turn nitrogen into ammonia or nitrates. Once a plant dies, other bacteria feed on the leftovers and turn nitrates back into gases like nitrous oxide or nitrogen.
BioFuels
As a strategy to lessen the dependence on oil and also reduce the pollution caused by fossil fuels, research on using biomass—agricultural and animal waste materials—to make biofuels started getting popular.
The source of these fuels were renewable and emitted less particulate pollution than gasoline and diesel fuels. At first, it was believed that bio-fuels contributed less to global warming, since the carbon dioxide (CO2) they emitted came from what they absorbed out of the atmosphere when they grew, unlike fossil fuels which emit large amounts of carbon that was removed from the atmosphere millions of years ago.
An example of biofuel would be Bioethanol, an alcohol made by fermentation of bagasse, the fibrous material left over after the extraction of sugar cane, corn or rapeseed. Biofuels may also be derived from forestry, agricultural or fishery products or municipal wastes, as well as from agro-industry, food industry and food service by-products and wastes.
Yet there are hurdles and counter-indicators for a switch over to bio-fuels that would require growing more crops to meet the demand, because it requires converting forests to agricultural land. Scientists have been debating whether producing them actually requires more energy than they can generate. The destruction of natural ecosystems not only releases greenhouse gases into the atmosphere when they are burned and plowed, but also deprives the planet of natural sponges to absorb carbon emissions. Cropland also absorbs far less carbon than the rain forests or even scrubland that it replaces.
Synthetic Greenhouse Gases From Industrial Processes
The stratospheric ozone layer above the Earth’s atmosphere protects us by absorbing the sun’s harmful ultraviolet (UV) rays. However, it has been discovered that the ozone layer above the Antarctic has become thin. Scientists pointed out that this was the result of the ozone layer being broken down by CFCs (Chloro fluorocarbons) used as refrigerants in air conditioners and refrigerators.
The extremely stable CFCs leak out, build up and spread in the lower atmosphere and reach the stratosphere, about 10 kilometers above the Earth’s surface, where the ozone layer is. Here, strong ultraviolet light breaks apart the CFC molecules and release chlorine atoms.
Ozone is constantly being produced and destroyed in a natural cycle in the stratosphere. What the presence of chlorine does is it accelerates the destruction process, and so the concentration of ozone falls and stabilizes at a lower level—the more chlorine, the lower the level.
Since ozone filters out ultraviolet radiation, less ozone means higher ultraviolet at the surface. The more depletion, the more skin cancer, cataracts, damage to materials like plastics, and harm to crops and sea life.
What Effect Do Greenhouse Gases Have on Climate Change?
Return to Ice Age?
Generally, rising concentrations of greenhouse gases produce an increase in the average temperature of the Earth, and in turn produce changes in weather and sea levels. Satellite images and research show the ice caps are melting faster, our sea levels are rising, and weather patterns are changing – water shortages, floods and cyclones, expanding deserts, loss of biodiversity, …
When the greenhouse effect warms the earth, it accelerates the hydrologic cycle, and rainfall increases in many places. This will slowly decrease the salinity of the North Atlantic, making the surface water less dense. Were a critical density threshold to be crossed, ocean circulation would abruptly switch to a new stable mode. This could usher a change in the way tropical heat is transported making some parts of the world – North Atlantic – 2 to 5 degrees colder on average than they are now, a slow transition to ice age.
Conclusion
Some scietists explain that what we now experience as global warming has been experienced in the past before half million years back in an era called Eemian age.The warm Eemian period from about 131,000 to 114,000 years ago—when the distribution of ice sheets was similar to what it is today—switched to the Wisconsin ice age in no more than 400 years. A similar situation exists now.
What are the chances that you may see cataclysmic climate changes in your life time? There are people who say global warming itself is a myth and they disagree that CO2 is the main driver of global warming.
To have a clear picture of global climate change we need to take all the factors involved in the greenhouse effect. For that, we may have to wait some more.
