London looks to count its carbon

By Jonathan Amos BBC News science reporter, in Baltimore

Urban planners will increasingly consider carbon "costs"London could soon have a network of scientific stations to monitor the great city's carbon "footprint".
The system would deploy instruments to track flows of gases such as carbon dioxide to get an idea of the capital's true contribution to climate change.
The proposal comes from researchers at King's College London.
The project's data could be used to guide future development decisions, ensuring London's carbon footprint is kept as small as possible.
"We know that cities are a major source of carbon but we don't understand the detail; there are very few studies," said KCL Professor Sue Grimmond.
Those that have been done in places such as Tokyo, Rome, Marseille and Copenhagen, show - not unexpectedly - that downtown areas produce large amounts of carbon, especially in winter months and in drive times when the roads are full of vehicles pumping out CO2.
Less well understood are the carbon contributions of the leafy suburbs of cities.
Professor Grimmond has been working on a project known as the Baltimore Ecosystem Study. It is a model for the type of monitoring she would now like to repeat in London.

Tree priority
In the Cub Hill district of the US city, instruments have been mounted on a 45m-high tower. They measure the movement of air and sample its concentration of carbon dioxide.
Three years of data show how the carbon footprint of this heavily treed, residential area varies through the year. In winter months, it is a source of carbon; but in summer months the large numbers of plants in its gardens and park areas actually take enough CO2 out of the atmosphere to make Cub Hill a "sink" for carbon.

Instruments are put high above the ground to get a broad pictureNonetheless, overall, the Baltimore suburb is a net contributor. And for Grimmond, this has lessons for city planners.
"As we put in new residential developments or new estates, if there is any way to preserve trees we should be trying to do it; and we should be encouraging people who have gardens to grow trees because they will sequester carbon," she said.
"Today, about 50% of the world's population live in urban areas. These areas only account for 2% of the Earth's surface but they are the major sources of carbon dioxide. We're expecting these urban areas to increase so that obviously has significant implications for CO2 sources."
Professor Grimmond was detailing her Baltimore work here at the American Geophysical Union Joint Assembly.
She told the BBC she now intended to set up similar experiments in London, probably at first instance in a central location close to KCL.
She envisages the capital eventually having an urban atmospheric observatory, which would link a network of monitoring sites to look at a range of environmental indicators.