Human activity sends greenhouse gases – in particular carbon dioxide (CO2) and methane (CH4) – into the atmosphere, which enhances the greenhouse effect.
Many of these gases come from fossil fuels such as oil, coal and natural gas used to run vehicles and to generate electricity for industries and households. When the atmosphere contains more greenhouse gases, the entire atmosphere and the Earth become warmer, as in a greenhouse.
Every year, WMO provides information on the state of global greenhouse gases.
Questions and answers
What is the greenhouse effect?
The Earth is warmed from the surface and not directly from the sun. Most greenhouses look like small glasshouses. They are commonly used technology to grow plants and vegetables, especially during the winter as they trap heat from the sun (long wave and short wave radiation). The glass panels of the greenhouse allow light in but keep heat from escaping. When energy from the Sun enters the Earth’s atmosphere, about one third of it is reflected back into space. Of the remainder, most is absorbed by the Earth’s surface. Some also stays in the atmosphere, absorbed by water vapour and greenhouse gases. This natural greenhouse effect is vital to life as we know it. At present, the average temperature on Earth is about 14°C. Without the greenhouse effect, the average temperature would be –18°C (32 degrees colder than the present temperature – too cold for most living beings).
What is the problem with greenhouse gases?
In 2009, there was about 38 per cent more carbon dioxide (CO2) in the atmosphere than in 1750. Global atmospheric concentrations of carbon dioxide and other greenhouse gases have increased markedly as a result of human activities. The more CO2 we put into the air, the more temperatures could rise. Two major activities that increase CO2 are the burning of fossil fuels and deforestation.
Forests are sometimes called “carbon sinks” because they take CO2 from the air and store it. When trees are cut down and burned, the CO2 that is stored in them is released back into the air. Scientists believe that every year, 2 billion to 5 billion tonnes of CO2 are released into the air from forests that are cut down and burned.