Greenhouse gas emissions have increased dramatically as more fossil fuels are burnt for both domestic and industrial purposes. When fossil fuels such as coal, oil and natural gas are burnt, the carbon in them combines with oxygen in the air to produce carbon dioxide. Land clearance and deforestation throughout the world have also contributed to this process. Carbon dioxide is a major greenhouse gas.

Greenhouse gases trap energy from the sun and warm the earth's atmosphere. The continued release of greenhouse gases from burning of fossil fuels and deforestation is raising the temperature of the earth and threatening many of the world's plants and animals with extinction. It is also increasing the incidence of extreme weather conditions such as droughts and flooding, and raising sea levels.

Trees, like all plants, sequester (absorb and store) carbon dioxide as part of the process of photosynthesis, which enables them to grow. Through this process, carbon dioxide is converted into stored carbon, and this is why trees are sometimes referred to as 'carbon sinks'. By taking this carbon dioxide from the atmosphere, trees clean the air, reduce temperatures, and counteract our polluting lifestyles.

Trees can also save as much as 10% of annual energy consumption around buildings by moderating the local climate keeping it cool in summer and warmer in winter. Tree canopies reduce rainstorm impact and provide a natural alternative to resource-heavy flood control systems that depend on hard engineering. And of course, in addition, trees add beauty to the urban landscape, filter harmful pollutants from the air, create vital wildlife habitats and tree planting is a wonderful way of bringing different communities together around a shared goal.

To mitigate your impact on the environment, Trees for Cities has worked out a formula of 2.67 trees planted for every tonne of CO2 generated. The charity believes this is a fair and cautious environmental payback for each tonne of CO2 emitted.

When the tree dies and rots down, the carbon locked away in its cells is released back into the environment. A growing tree absorbs as much carbon from the environment as a rotting tree releases so it's important to replace trees that have died; this is the carbon neutral cycle.

To mitigate the carbon that we release in other ways - for instance, through air travel or manufacturing - we need to do more than simply replace the trees that have died; we need to plant new ones.

Tree planting in urban areas is a great way to give something back to the environment. Trees are highly 'carbon smart' and, as well as absorbing atmospheric carbon dioxide, can help mitigate against climate change in a number of ways:

• Trees can also save as much as 10% of annual energy consumption around buildings by moderating the local climate keeping it cool in summer and warmer in winter.
• Tree canopies reduce rainstorm impact and provide a natural alternative to resource-heavy flood control systems that depend on hard engineering.
• Trees help to filter harmful pollutants from the air, making areas with many trees healthier places to be than areas without trees.
• Trees create vital wildlife habitats, enabling more species to thrive in their surroundings.

In addition to their positive physical differences to the environment, trees also add beauty to the urban landscape, and tree planting is a wonderful way of bringing different communities together around a shared goal.