By signing up to international carbon reduction targets, world leaders have issued a challenge to everyone involved in urban space design. Whilst we cannot realistically claim that planting trees in towns will significantly affect global climate, what we do know is that they have a major role to play in city climate mitigation and adaptation strategies.
Trees can, by providing shade and cooling through transpiration and evaporation processes, reduce temperatures around them. Clusters of well established trees probably represent the most effective tool available to urban designers in combating urban heat islands and heat sinks in cities. These pockets of heat accumulate in urban areas as a result of solar energy and glare reflected off engineered hard surfaces. These same surfaces store the heat and release it over night, scarcely having time to cool before the next sun rise.
One well-established tree can have the effect of 10 room-sized air conditioners – but of course from a totally sustainable, zero energy source.
The targets set for CO2 reduction are extremely challenging – by 2020, a reduction of 1.2m tonnes of CO2 per annum is looked for in the UK, and by 2050 a reduction target of 80% of 2009 levels. If trees are to play a part in implementing this reduction, a lot needs to happen quickly.