Greenwich Park 3\Times Newspapers Ltd

TWO million trees should be planted in London to combat rising temperatures, an environment chief has said.

Average summer temperatures in the city could rise by 3.9C by 2080, and up to 10C on the hottest days, it has been predicted.

Boris Johnson's environment adviser Isabel Dedring said London needs more parkland to offset the higher temperatures.

The "urban heat island effect" in which buildings absorb and release heat, maintaining a higher temperature in cities than surrounding areas, means London temperatures will continue to be higher than other parts of the South East.

The Mayor's environment plan is aiming to increase tree cover across the capital by 5 per cent - an extra 2million trees - by 2025 as part of efforts to create a more environmentally friendly capital.

The programme, Leading to a Greener London, also involves plans for an increase in green space in inner London by 5 per cent, including green roofs and more street trees.

A green roof is a roof consisting of various waterproofing and drainage layers topped with soil and plants.

Other measures to make the capital "greener, cleaner and more civilised" include pilot schemes that will pay householders to recycle.

The "RecycleBank" trials will take place in up to five outer London boroughs which have green recycling wheelie bins and will give residents vouchers in return for the amount of waste they recycle - using technology to weigh their bins when they are collected.

Other schemes that form part of the environment policy include a district heating project and programmes to retrofit existing homes and buildings to make them more energy efficient.

London is even backing trials for biodegradable gum, while low-energy traffic lights will be installed from 2010.

Ms Dedring said: "People really struggle to see how an old, Victorian built-up city like London can really be a low carbon city, which if you look at the targets, it needs to be."

She said that while projected temperature rises were a long way off, action had to be taken now to prepare for the future.

"There are lots of things we can do collectively to offset those rises, and we have to start doing that now," she said.

She warned that "if we all panic and stick in air conditioners it will make things worse", as the energy needed to run them would add to emissions and London's streets would be unbearably hot in the summer.

Instead, greening London through planting street trees - with 1,400 already planted, and 10,000 new trees planned - would help to keep temperatures down.

"Trees in streets have a very positive air quality effect, as well, - certain kinds of trees absorb pollutants," she added.