What causes climate change?
Just as the world’s most respected scientific bodies have confirmed that the Earth is getting hotter, they have also stated that there is strong evidence that humans are driving the warming (2).
Scientists agree the main cause of climate change is human activities which magnify the ‘greenhouse effect’ – a natural process in which gases in the atmosphere warm the Earth by trapping heat that is radiating towards space (2) (4).
A layer of greenhouse gases, including water vapour and smaller amounts of carbon dioxide, methane and nitrous oxide, act as a thermal blanket surrounding the Earth. This absorbs heat and warms the surface to a life-supporting average of 15°C. As energy slowly escapes out of our atmosphere, some of it is absorbed by the greenhouses gases, which warms the Earth further. Although these gases are present naturally, human activity is increasing their concentrations, thereby exacerbating the greenhouse effect (4).
Carbon dioxide (CO2) is the main greenhouse gas of concern. A finite amount of carbon is stored in fossil fuels, the sea, living matter and the atmosphere. Without human influence there is a fine balance in the amount of carbon in these stores, but when humans cut down trees or burn fossil fuels, they release extra carbon into the atmosphere (4).
Warming caused by man-made emissions of greenhouse gases also increases the amount of water vapour in the air by boosting the rate of evaporation from the oceans and elsewhere. This amplifies the warming effect, as well as the amount of rain and snow falling to Earth which can lead to extreme weather patterns (4).
The greatest source of man-made emissions is the burning of fossil fuels (2). As the world’s population grows, more people are burning fossil fuels for energy. By driving cars, heating our homes with oil, gas, or electricity from coal-fired power stations, we release greenhouse gases into our atmosphere. In 2005, burning fossil fuels sent about 27 billion tonnes of carbon dioxide into the atmosphere (8).
Food production also leads to the burning of fossil fuels. Land must be cleared for farming, which often contributes to deforestation. Food is also often transported across the world to reach distant markets, meaning fossil fuels are burnt in the process. Fertiliser production for crops and methane gas emitted by livestock also contributes to emissions.
Scientists estimate that forest loss and other changes to the use of land account for around 23 percent of current man-made carbon dioxide emissions (9). This is because forests are a natural ‘sink’ of carbon dioxide. By harnessing the sun’s energy, plants absorb carbon dioxide from the air as they grow, turning the carbon molecules into the building blocks of their trunks, branches and leaves. But when forests are cleared or burned, their stored carbon is released back into the air, contributing to global warming (9).