Have we been lied to about the quality of the air we breathe? Do car manufacturers, regulators and farmers have some explaining to do about their emissions to the atmosphere? Tom Heap investigates.

Producer: Martin Poyntz-Roberts.

Urban Britain is paving over its front gardens. Lawns, hedges and hollyhocks are being replaced by tarmac and car ports. Each garden may be tiny, but with over 50 million front gardens in the UK, the numbers really add up. It's an environmental problem, quite literally on our doorsteps, and Jheni Osman is finding out what can be done about it.

In Ealing, West London, Jheni meets Leigh Hunt, Horticultural Adviser to the RHS. He reveals that according to their statistics a quarter of all gardens in the UK are now completely under the asphalt. Added together, these tiny patches of grey contribute to many environmental problems - flash floods caused by rain run-off; the 'urban heat island' effect from bricks and mortar which act like storage heaters; and the loss of all-important wildlife corridors for the birds and bees of the cities.

Meanwhile, up in the North of England, Jheni takes a look at how it SHOULD be done. With Horticulturalist Nigel Dunnett, she takes a walk around green and lush suburban Sheffield and spots innovative planting solutions to the problems of urban paving. Nigel tells her about the devastating floods which swept through Sheffield in 2007, and donning her hard hat, Jheni takes a look at the city's ingenious response to the disaster - a radical transformation of a former dual carriageway into a 1.3 kilometer green-way and 'Rain Garden'.

Back in Bristol, Jheni visits two examples of the trend being bucked. A thriving bat colony roosting in an urban garden is a haven for all sorts of wildlife, and a communal planting scheme which is transforming the hard grey of the city centre into a food-growing paradise, complete with runner-beans and sweetcorn.

Perhaps there is hope for our gardens yet.

Produced in Bristol by Emily Knight.

As the oceans absorb manmade carbon emissions a chemical reaction takes place which is making sea water more acidic. This subtle shift in pH level is having a profound effect on the sea animals which use calcium carbonate to form their shells and skeletons and Marine Biologists are now discovering that this could have implications across the world's oceans. Already shellfish industries in America are being adversely affected and scientists are working hard to predict how the world's fisheries might respond in the future. Professor Alice Roberts discovers there are surprising lessons to be learnt from the past and hears why immediate action is needed to prevent further threats to biodiversity.

Producer: Helen Lennard.

Britain still owns islands large and small across the globe, from Pitcairn to South Georgia and Bermuda to Ascension. Could we use the waters around these territories to protect vast swathes of the oceans from overfishing and development? Tom Heap meets the islanders and the conservationists eager to see if Britain really can lead the way.

He takes to the water to see how Gibraltar is using its spawning grounds to restore the health of the Mediterranean and finds out what the enormous new no-fishing zone around Pitcairn could mean for the Pacific.

Producer: Alasdair Cross.

How noisy is the underwater environment? Tom Heap dips beneath the surface to find out if man-made noise is affecting the marine life that lives below the waves.

Costing The Earth begins a new series with three programmes investigating the health of our oceans. The team tackles ocean acidification and how the UK plans to protect marine areas in its overseas territories but first Tom Heap delves into a mystery soundscape: one that exists underwater.

Scientists are only just beginning to study the complex noises coming from beneath the waves. All marine life depends on sound to communicate but in a world that is becoming increasingly loud, whales, dolphins, fish of all shapes and sizes, all the way down to molluscs and the smallest organisms are finding their voices lost in a sub-aqua world of rumbles and crunches from various man-made sources.

Presenter: Tom Heap

The little Scottish island of Eigg is teaching the world how remote communities can power themselves with clean, green energy. Tom Heap meets the locals who've built the pioneering system and the international visitors who are eager to learn their secrets.

Producer: Alasdair Cross.

In May 1985 Joe Farman, Jonathan Shanklin and Brian Gardiner of the British Antarctic Survey published their paper in the scientific journal Nature. It revealed there was a large and expanding hole in the ozone layer above the Antarctic and that the cause was the chlorofluorocarbons or CFCs then commonly used in aerosols and refrigerants.

The size and speed at which the hole had formed was alarming and the paper helped convince governments across the globe to take action. The resulting Montreal Treaty of 1987 has been called the most successful environmental legislation ever passed. CFCs were effectively banned and their prevalence in our atmosphere has been slowly decreasing. The ozone layer hole does appear to be healing but the process is slow and increasingly complicated.

Today the interplay between ozone and the greenhouse effect is only just becoming understood and even more worrying is new research which points to previously unknown CFCs and other ozone depleting substances accumulating in the stratosphere. BBC weather forecaster, Peter Gibbs celebrates the discovery which saved millions from skin cancer and hears about the need for continued vigilance.

Producer: Helen Lennard.

How will the next government tackle Britain's environmental problems?

The politics of the environment and our food supply are vital for the future of the planet.

Tom Heap hosts a debate asking if this election campaign has raised the issues that need addressing.

What specific commitments have the political parties made on nature? Where are the big ideas to tackle climate change? How can we secure our food supplies without wrecking the planet?

Tom Heap will put these challenging issues to a panel that features philosopher, Roger Scruton, former Executive Director of Friends of the Earth, Tony Juniper, Chief Executive of the Soil Association, Helen Browning, Director of Forum for the Future, Jonathon Porritt and Heather Hancock, lead author of the independent review of the BBC's coverage of rural affairs.

Presenter: Tom Heap

China has powered its development with water. When it needed energy for industry it built the largest hydro-electric dams in the world. When the farmland and factories of northern China were threatened with drought an enormous canal was built to pipe supplies from the south. China has the engineering skill, the capital and the will to challenge the limits that nature sets on development. But the exploitation of China's water resources has come at a great cost, forcing millions from their homes, polluting natural lakes and rivers and pushing rare animal species to the brink of extinction.

Isabel Hilton, editor of the China Dialogue website, assesses the progress of China's water revolution and asks where its water will come from in the future. Can large-scale engineering continue to provide the answers or must government teach industry and the public to live within their means?

Producer: Alasdair Cross.

Tom Heap investigates whether eco-cities are living up to their promise.

In years gone by, Costing the Earth has visited two eco-cities, which both promised that rapid urban development could be green, sustainable and profitable. Dongtan in China was meant to be part of "the quest to create a new world", according to British designers Arup. Masdar in the Arabian Gulf was to have "changed the world", according to British architect Norman Foster. But Dongtan never got built, thanks to Chinese political machinations and corruption, while Masdar has stalled, a victim of the world economic crisis.

China is still pressing ahead with over 100 new eco-cities. But does the idea of the eco-city make sense anyway? Critics say that some very ordinary new cities are being branded as "eco" in an attempt to give them a green marketing gloss, and that promoting the idea of the virtuous self-contained eco-city can mask a failure to build sustainably in the rest of the economy.

Producer: Jolyon Jenkins.