主题：【自然生态】What is climate change?

What is climate change?
People talk a lot about the weather, which is not surprising when you consider the impact it has on our mood, on how we dress and on what we eat. 'Climate' however is not the same as the weather. It is the average pattern of weather for a particular region over a long period of time.

The climate has and will always vary for natural reasons. Natural causes of this include fractional changes in solar radiation, volcanic eruptions that can shroud the Earth in dust which reflects the heat from the sun back into space, and natural fluctuations in the climate system itself.

However, natural causes can explain only a small part of this warming. The overwhelming majority of scientists agree that it is due to rising concentrations of heat-trapping greenhouse gases in the atmosphere caused by human activities.

Understanding Climate Change
Energy from the sun warms the earth's surface and, as the temperature increases, heat is radiated back into the atmosphere as infra-red energy. Some of the energy is absorbed within the atmosphere by 'greenhouse gases'.

The atmosphere acts in a similar way to the walls of a greenhouse, letting in the visible light and absorbing the outgoing infra-red energy, keeping it warm inside. This natural process is called the "greenhouse effect." Without it, the global average temperature on earth would be -18°C, whereas at the moment it is +15°C.

However, human activities are adding greenhouse gases, particularly carbon dioxide, methane and nitrous oxide, to the atmosphere, which are enhancing the natural greenhouse effect and making the world warmer. This man-made extra warming is called the "enhanced" greenhouse effect.