A worldwide tree planting campaign is aiming to reach a total of 7 billion by the end of 2009 – that means just over one for everyone on the planet.

The United Nations says the campaign has exceeded expectations since it began in late 2006 with a goal of planting one billion within a year: two billion have been planted already. That means another 5 billion by late 2009.

A lot of the plantings so far have been by carried out governments —  including 700 million by Ethiopia, 400 million by Turkey and 250 million by Mexico. That still leaves a lot still to be planted by companies and people like you and me.

Of course it leaves questions about how many survive — there are no checks to see if the saplings — like the one in the photo being planted by Kenyan Nobel Peace Prize winner Wangaari Maathai (right) in 2006, grow to maturity. 

Trees absorn carbon dioxide, the main greenhouse gas, as they grow and release it when they rot or are burned. So planting trees can take a chunk out of global warming — a U.N. official says that 7 billion trees would, if they reach maturity, soak up as much greenhouse gases as Russia emits in a year.

Have you noticed more trees in your neighbourhood? Or have you planted any?