Since the mid-nineteenth century, close to 1,100 billion tonnes of greenhouse gases have been released into the atmosphere²². Historically, the largest contributors to atmospheric greenhouse gases have been the developed countries. The United States for example, accounts for 20% of carbon dioxide emissions, but only for 4.6% of the world’s population²³.

Today however, the realities are rather different. Developing countries, with their larger populations than industrialized ones, have entered into the intensive stages of economic development, and are adding to global emissions. To provide a comparison, between 1990 and 2008, carbon dioxide emissions grew by 27 percent in the US, but by 150 percent in China²³.
To get an idea of the pace of development, sample this: the International Energy Agency (IEA) had predicted in 2004, that China would surpass US emissions by 2030. That no longer appears to be true, as China seems to have surpassed US emissions in 2006 - 2007.

All these emissions arise from the burning of fossil fuels for industrialization and development, and through deforestation. Some of the major human activities that result in greenhouse gas emissions are power generation (25%), deforestation (20%), road transport (13%), oil and gas production (6.3%), fertilizer production (6%), livestock (5.1%), cement production (4%), aviation (3.5%), iron and steel manufacture (3.2%) and waste production (3%).

See the pie chart below to see the contribution that the most important greenhouse gases make to global emissions.

Continued emissions will mean that the world will experience a radical transformation of its climate². Such changes threaten the basic requirements of people around the world - access to food and water, use of land, and issues of health and environment¹.