The major reason of global warming is due to human activities,the green house gases such as carbon dioxide and nitrogen oxides produced by the industry traps the energy from the sun.If there is no such gas in the atmosphere,the earth will be too cold for any living organism to survive,it is natural to have some green house gases in the air and some people argue that even without human effect there are evidences show that the temperature of the earth increase and decrease in cycles,and now we are reaching another ice age.One of the concerns is that the green house gases increased so fast that it is now a big threat to all the species on the earth.The human activities that cause global warming are deforestation which means that less carbon dioxide can be converted back into oxygen,use of fossil fuels which releases the carbons that accumulated for many years and the consequences are the rising of sea level,melting of ice in the Antarctic and increase in temperature.Rising in sea level means that the space for the land organism decreases.Melting of ice mean the release of any harmful substances that may have been trapped thousand of years ago and also cause a further rise in sea level.The increase in temperature will also provide a better condition for bacteria and virus to grow which means more diseases.