What causes climate change?
Through years of observations, scientists have now developed an understanding that climate change is the result of greenhouse gases caused by human activity, since the Industrial Revolution. In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change (IPCC), a group of independent scientific experts from all over the world, concluded there's a more than a 95% probability that human activities over the past 50 years have warmed our planet.
Greenhouse gases include water vapour, nitrous oxide, carbon dioxide and methane, which act as a blanket around the Earth. These gases absorb heat, which is then re-emitted in all directions, stopping the suns radiation from bouncing back into space.
- Carbon dioxide is released from human activities such as burning fossil fuels, deforestation and land use changes. Since 1950, the global carbon dioxide emissions from human activity have increased by over 400% (Committee on Climate Change). Atmospheric CO2 is at its highest level for at least 800,000 years, reaching over 400 parts per million today (Met Office).
- Methane occurs in much smaller quantities than Carbon Dioxide, but it produces 21 times as much warming as CO2. About two thirds of methane comes from man made sources such as the burning of fossil fuels and drilling for natural gas, but it is also a gas which is produced naturally (BBC Weather Centre).
- Nitrous oxide, when released in large amounts contributes significantly to global warming. Sources include car exhaust fumes and the use of synthetic fertiliser in agricultural activities. Though it makes up an extremely small part of the atmosphere, it is 200 to 300 times more effective at trapping heat that CO2 (BBC Weather Centre).
- Halocarbons include a variety of different gases, and they very rarely occur naturally. They are found in products like refrigerators, air conditioning and aerosol cans. The most well known gases within this area are CFCs.
- Water vapour is a ‘feedback’ greenhouse gas and also the largest contributor to the ‘greenhouse effect.’ Cold air holds very little water vapour but warmer air can contain up to 4% water vapour. As air temperatures increase through climate change, more water vapour can be held in the atmosphere causing positive feedback (see below for an explanation of a feedback loop).
A feedback loop refers to a vicious circle, with a positive feedback accelerating temperature rise, and a negative feedback slowing down warming.
The impact of melting ice is one example of a positive feedback loop in climate change. Because ice is white, it has what is called a high albedo, which means high reflectivity. This means that ice reflects the suns rays back into space, limiting the amount of warming. However, once the ice melts, the darker coloured water below the ice is revealed. This darker coloured water absorbs more of the suns radiation, which in turn leads to more warming and more ice melting and so on.
Date of Publication: 5.07.2018