Global Climate Change One of the major effects of greenhouse gas emissions will be global warming. Assuming that no actions are taken to reduce emissions, computer models of the earth's climate predict that global average temperatures will rise by 1.5 to 4.5 degrees C over the next 100 years. This rise is larger and probably faster than any such change over the past 9,000 years. The consequences of global warming will be serious for both human beings and the ecosystems which support all life on earth. Average sea levels may rise, rainfall patterns change, agriculture affected by temperature, soil and moisture changes, and water resources threatened.
Human beings increase greenhouse gas levels in the atmosphere through many daily activities.
When we burn fossil fuels such as oil, coal, and natural gas, we release the carbon dioxide that has been stored in them for thousands of years. Massive burning of fossil fuels in just a few recent decades has emitted tremendous amounts of CO2. A further source of CO2 is cement production. Living, growing trees help to absorb carbon dioxide from the atmosphere, so our present trend towards deforestation of the planet means that less carbon dioxide is being absorbed. Humans are responsible for other greenhouse gases as well.