Without these greenhouse gases,it's estimated the earth's temperature would be about minus 18 degrees celsius . Unfortunately , too many of these heat-trapping gases have been released into the atmosphere over the past 200 years mainly through human activities as for example deforest. As a result the world is retaining more heat - this is called the enhanced greenhouse effect. This effect utlimate leads to changes in the local and global climate if not contained and managed appropriately. This is what is commonly called climate change.