Scientists looking at the effect global warming will have on our major cities say a modest increase in the number of urban parks and street trees could offset decades of predicted temperature rises.

The University of Manchester study has calculated that a mere 10% increase in the amount of green space in built-up centres would reduce urban surface temperatures by as much as 4C.

This 4C drop in temperature, which is equivalent to the average predicted rise through global warming by the 2080s, is caused by the cooling effect of water as it evaporates into the air from leaves and vegetation through a process called transpiration.

"Green space collects and retains water much better than the built environment," explained Dr Roland Ennos, a biomechanics expert in Manchesters Faculty of Life Sciences and a lead researcher in the team.

"As this water evaporates from the leaves of plants and trees it cools the surrounding air in a similar way to the cooling effect of perspiration as it evaporates from our skin."

Taking Greater Manchester as their model, the team used Geographic Information System (GIS) mapping to build up a picture of the conurbations land use. The team then worked out the impact that increasing the amount of green space would have on the urban climate as well as on water retention.

"Urban areas can be up to 12C warmer than more rural surroundings due to the heat given off by buildings, roads and traffic, as well as reduced evaporative cooling, in what is commonly referred to as an urban heat island," said Dr Ennos, who worked on the project with Professor John Handley and Dr Susannah Gill in the School of Environment and Development.

"We discovered that a modest increase of 10% green space reduced surface temperatures in the urban environment by 4C, which would overcome temperature rises caused by global warming over the next 75 years, effectively climate proofing our cities.