OSLO — A campaign to plant trees worldwide set a goal on Tuesday of seven billion by late 2009, just over one for each person on the planet, to help protect the environment and slow climate change.

The UN Environment Program (UNEP), an organizer of the tree planting drive begun in late 2006 with an initial goal of a billion by the end of 2007, said governments, companies and individuals had already pushed the total above 2 billion.

It set a target on Tuesday of an extra five billion plantings by the time a UN climate conference in Denmark starts on November 30 next year that is meant to agree a new long-term treaty to combat climate change beyond the UN’s Kyoto Protocol.

"In 2006 we wondered if a billion tree target was too ambitious; it was not," said Achim Steiner, head of UNEP.

"The goal of two billion trees has also proven to be an underestimate. The goal of planting seven billion trees, equivalent to just over a tree per person alive on the planet, must therefore also be do-able," he said in a statement.

UNEP said that safeguarding and planting forests were among the most cost-effective ways to slow climate change, blamed by the UN Climate Panel on emissions of carbon dioxide from burning fossil fuels in factories, power plants and cars.

Trees soak up carbon dioxide as they grow and release it when burnt or when they rot. Deforestation accounts for over 20 percent of the carbon dioxide humans generate.