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.
Methane is released through intensive agriculture, coal mining, and leaky natural-gas lines. Nitrous oxide and low- altitude ozone levels are also increasing rapidly, for reasons that are less clear. Less than 200 years since human beings began making major emissions, greenhouse gas concentrations are rising to levels higher than any yet seen while humans have existed on this planet - and they will rise much further in the years ahead. Greenhouse gases from human activities In 1987, the base year for many CO2 reduction plans, 20.5 billion tonnes of carbon dioxide were pumped into the atmosphere. This means that the industrial world carries the main responsibility for global warming.