Global warming means increase in the average temperature of the oceans and atmosphere on the scale of the entire planet over several years. It started in the 19th century and it still continue. The average temperatures have increased by 0.2 to 0.6 ° C. Especially in the last 25-50 years the global warming considerably contributes human activities, particularly greenhouse gas emissions, such as carbon dioxide (CO2). A warmer Earth may lead to changes in rainfall patterns, a rise in sea level, and a wide range of impacts on plants, wildlife, and humans. Warming is expected to be strongest in the Arctic and would be associated with the retreat of glaciers and sea ice.
Source: http://en.wikipedia.org/wiki/Global_warming
