What is global warming?


    What is global warming? Over the last 10,000 years, Earth’s thermostat has been set to an average surface temperature of about 57°F. However, global average temperatures have been rising due to enhanced atmospheric concentrations of carbon dioxide (CO2), methane (CH4), nitrous oxides (NOx), sulfuric oxides (SOx) and other “greenhouse gases.” These gases allow incoming solar radiation (visible light) to warm the surface of the Earth (Fig. 1). The Earth then radiates this received energy outward in the form of infrared radiation. The molecular structure of greenhouse gases (GHGs) makes them very effective at absorbing this infrared radiation and re-radiating it both out to space and back to Earth’s surface.
    While this greenhouse effect has had a moderating effect on Earth’s temperature for millions of years, the dramatic increase in fossil fuel use since the late 1800s has led to ever-increasing atmospheric concentrations of GHGs. Higher GHG concentrations have prevented greater and greater amounts of the Earth’s own infrared radiation from escaping to space, causing surface temperatures to rise over the past century. Higher global average temperatures are only one result of increased GHG levels: temperatures at high northern latitudes have warmed more than temperatures at other latitudes, extreme weather events have become more frequent, and precipitation patterns are changing, as well.
    As our understanding of the complex nature of these effects has grown, the term “global warming” has no longer been as widely used. Instead, “global climate change” is the term most frequently employed to describe this highly variable climatic response.
    What are the effects of global warming?
    Of the many effects of climate change, some of the most likely and most potentially harmful include:
    Rising sea level: Global average sea level rose about 7 inches (17 cm) over the 20th century. This increase is largely due to the warming of the oceans during this time, which has caused ocean water to thermally expand. The rate of sea level rise is expected to increase in coming years due to melting of mountain glaciers and of the Greenland and Antarctic ice sheets. By the end of the 21st century, sea levels are estimated to rise another 8-24 inches (20-60 cm)2, displacing coastal populations, significantly accelerating shoreline erosion, causing greater amounts of flood damage, and increasing levels of  fresh-water contamination.
    Receding snow pack: Mountain glaciers and snow cover have been declining worldwide and are expected to continue to contract. Reduced snowfall will strongly affect freshwater availability for billions of people who depend on river flow from the Himalayas, Andes, Rockies and other mountain ranges for
    fresh water for agricultural, industrial and domestic use.
    Ocean warming and acidification: As atmospheric CO2 concentrations increase, the ocean absorbs CO2 from the air, which causes seawater to become increasingly acidic. Acidification, combined with warmer ocean temperatures, is likely to be dangerous for a wide range of ocean species that have evolved to live within narrow temperature and pH ranges. Coral reefs, which are home to a quarter of the biological species in the ocean,3 are especially at risk. Fisheries will likely be affected as well due to species migration.
    Disappearance of Arctic sea ice: GHG-related climate change causes temperatures to increase more at high northern latitudes than at other locations around the world. This high-latitude warming has resulted in reductions in Arctic sea ice, especially in the late Summer/early Fall when ice extent reaches its seasonal minimum.4 Climate modeling studies indicate that this trend will continue; in some projections, late summer sea ice is expected to disappear entirely before the end of the 21st century. Both people and wildlife that depend on sea ice for hunting and fishing are threatened by this change. The loss of Arctic sea ice may become a source of political conflict as different countries vie for access to and ownership of
    these newly opened shipping lanes.
    Heavier storms and more intense droughts: Over the past several decades storms over land areas have become more intense and more frequent. This is consistent with the fact that in a warmer environment, the atmosphere can hold much greater amounts of water vapor. Conversely, more intense droughts have been observed over wider areas since the 1970s. Increases in drought intensity and length have occurred mainly in the tropics and subtropics, and these trends are expected to continue, especially in Northern Africa, the Sahel, the Mediterranean and Central America. Climate projections also indicate that the upward trend in intense precipitation events is highly likely to continue, accompanied by the potential dangers of flooding and agricultural damage.
    Southern African Alternative Energy Association (SAAEA) is promoting green alternative energy solutions to combat global warming.