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When energy from the Sun hits the surface of Earth, some of it is absorbed and some of it is reflected back. Some of this reflected energy passes through the atmosphere into space, but some of it is reflected back again to Earth.

This is why it is hot sitting in a car or greenhouse on a sunny day, and so is called the greenhouse effect. Without the greenhouse effect the mean temperature on Earth would be -18°C and there would be very little or no life.

The greenhouse effect traps some of the energy from the Sun, which keeps our planet at a suitable temperature for life.

However, our increased release of gases such as carbon dioxide and methane is causing an increase in the greenhouse effect called the enhanced greenhouse effect. This is leading to climate change. Some of the effects of climate change are:

• disruption to the growth of crops for food
• changes in weather including drought in some areas and severe storms leading to flash floods in others
• an increased average temperature (global warming) – see below
• which in turn increases the severity of wildfires
• increased extinctions
• increased spread of tropic diseases

Global warming

Global warming is the increase in the mean temperature of the Earth. The ten hottest years since records began have been in the last 30 years. The mean increase in the last 100 years has been less than 1°C. This might seem small, but is enough to have devastating consequences on many species in different parts of the world.

As the percentage of carbon dioxide in our atmosphere has increased so has the Earth's mean temperature. Note that the shape of the first graph showing the amount of carbon dioxide in the atmosphere is exponential and is a similar shape to graphs showing human population change over the same time period. When comparing graphs such as changes to carbon dioxide levels and temperature against time, note that the axes are drawn to different scales, and do not start at '0'.

The consequences of global warming are:

• melting of the polar ice caps
• the rise in sea level may one day threaten many cities such as London, New York and Amsterdam
• weather patterns will change with more unusual weather
• animals will migrate towards the poles to find habitats with suitable temperatures
• tropical diseases may become more common in other regions, such as Europe
• change in distribution of pests that attack crops, which will have an impact on food security in some areas
• many species will become extinct

The rate of global warming can be reduced by reducing the rate at which greenhouse gases are being released. For example:

• using energy resources more efficiently, eg more cars with a higher fuel efficiency
• using renewable sources of energy (eg solar power) instead of fossil fuels
• reducing waste by recycling (eg plastic bottles)
• reducing deforestation (eg reducing the conversion of rainforest to farmland)
• developing techniques to capture and store the carbon dioxide released from power stations