Global warming begins when sunlight reaches Earth. The clouds, atmospheric particles, reflective ground surfaces and ocean surface then reflected about 30 percent of it back into space, while the remaining is absorbed by oceans, lands and air. This in turn heats the planet’s surface and atmosphere, making life possible. As Earth warmed up, this solar energy is radiated by thermal radiation or infrared heat, travelling directly out to space, thus cooling the Earth. However, some of the outgoing radiation is re-absorbed by carbon dioxide, water vapor and other gases in the atmosphere and is radiated back to Earth’s surface; these gases are known as greenhouse gases due to their heat-trapping capacity. This re-absorption process is naturally good; the Earth’s average surface temperature would be very cold if not for the greenhouse gases.
The problem begins when the concentration of greenhouse gases in the atmosphere were artificially raised by humankind at an ever-increasing rate since the past 250 years. As of 2004, over 8 billion tons of carbon dioxide was pumped out per year; natural carbon sinks such as forests and the ocean absorbed some of this, while the rest accumulated in the atmosphere. Millions of pounds of methane are produced in landfills and agricultural decomposition of biomass and animal manure. Nitrous oxide is released into the atmosphere by nitrogen-based fertilizers and other soil management practices. Once released, these greenhouse gases stay in the atmosphere for decades or longer. According to the Intergovernmental Panel on Climate Change (IPCC), carbon dioxide and methane levels have increased by 35 and 148 percent since the 1750 industrial revolution. Paleoclimate readings taken from ice cores and fossil records dating back to 650 000 years show that both gases are at their highest levels. Thermal radiation is obstructed further by the increased concentrations of greenhouse gases, resulting in what is known as enhanced global warming.
Recent observations of global warming have solidified the theory that it is indeed an enhanced greenhouse effect that is causing the world to warm. The planet has experienced the largest increase in surface temperature over the last century. Between 1906 and 2006, the Earth’s average surface temperature rose between 0.6 to 0.9 degrees Celsius; the last 50 years saw the temperature increase rate almost doubling. Sea levels have shown a rise of about 0.17 meters during the twentieth century. The extent of Arctic sea ice has steadily shrunk by 2.7 percent per decade since 1978, just as world’s glaciers steadily receded.
As the world continues to consume ever more fossil fuel energy, greenhouse gas concentrations will continue to rise, and with them Earth’s temperature. The IPCC estimates that based on plausible emission scenarios, average surface temperatures could increase between 2°C and 6°C by the end of the 21st century. Continued warming at current rates poses serious consequences. Low-lying coastal regions, with dense population, are especially vulnerable to climate shifts, with the poorer countries and small island nations having the hardest time adapting. It has been projected that by 2080, 13 to 88 million people around the world would lose their home to floods.