The green house effect is the process by which absorption and emission of infrared radiation by gases in the atmosphere warm a planet’s lower atmosphere and surface. The sun is the Earth’s primary energy source, a burning star so hot that we can feel its heat from over 150 million kilometers away. Its rays enter our atmosphere and shower upon on our planet. About the third of the solar energy is reflected back into the universe by shimmering glaciers, water and other bright surceases. Two thirds, however, are absorbed by the Earth, thus warming land, oceans, and atmosphere. Much of this heat radiates back out into space, but some of it is stored in the atmosphere. This process is called the greenhouse effect. Without it, the Earth’s average temperature would be a chilling – 18° degrees Celsius, even despite the sun’s constant energy supply. In a world like this, life on Earth would probably have never emerged from the sea. Thanks to the greenhouse effect, however, heat emitted from the Earth is trapped in the atmosphere, providing us with a comfortable average temperature of 14 degrees.
Human activity since the Industrial Revolution has increased the amount of greenhouse gases in the atmosphere, leading to increased radiative forcing from CO2, methane, tropospheric, ozone, CFCs and nitrous oxide. The concentrations of CO2 and methane have increased by 36% and 148% respectively since the mid-1700s.
These levels are much higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores.
Less direct geological evidence indicates that CO2 values this high were last seen about 20 million years ago. Fossil fuel burning has produced about three-quarters of the increase in CO2 from human activity over the past 20 years. Most of the rest is due to land-use change, particularly deforestation. In what seems like nature’s brutally irony, the gases that make life on Earth possible now threaten our very existence.