By Alex Kirby
BBC News Online environment correspondent in Jeju, Korea
The world seems to have begun to turn greener, in the strictly literal sense, according to the United Nations Environment Programme (Unep).
About a third of the world is still covered with forests...
Satellite data show plant growth has been measurably more vigorous over the last 25 years.
The news comes in Unep's first Global Environment Outlook Year Book 2003, which highlights trends and problems.
The book is being launched at the opening here of Unep's annual council, attended by about 150 delegations.
The meeting runs from 29 to 31 March.
Satellite and climate data between 1982 and 1999 show an "apparent greening of the biosphere", Unep says.
"The amount of energy produced by plants through photosynthesis, minus what they use in respiration, increased globally by about 6% during the last two decades of the 20th century," it adds.
Advances in farming and successful conservation programmes around the world may have contributed to the greening trend, according to the organisation.
... but access to water remains a big problem worldwide.
Unep says areas in tropical zones and in the high latitudes of the Northern Hemisphere accounted for 80% of the increased growth.
Nearly 40% came from the Amazon rainforests, probably because of a decline in cloud cover and the resulting increase in solar energy reaching the surface.
Changes in monsoon dynamics meant more rainfall in the 1990s and increased vegetation over India, Pakistan and Bangladesh and the Sahel belt of sub-Saharan Africa.
The Geo Year Book 2003 is the first in an annual series published to complement Unep's encyclopaedic Global Environment Outlook reports - the third of which was published in 2002.
The new publication reviews major developments during the year, identifies developing challenges, and gives details of progress on key indicators like greenhouse gas emissions, and threats to animals and plants.
It says the economic losses these cause are estimated to have multiplied five times since the 1970s, to a total of $629bn for the 1990s.
A special feature examines the prospects for reaching international goals on providing more people with water, including the Millennium Development Goal - agreed by world leaders in 2000 - to halve by 2015 the proportion of people without access to safe drinking water.
Unep executive director Klaus Toepfer says: "Without concerted action, about a third of the world's population is likely to suffer from chronic water shortages within a few decades."
Much of the meeting will be given over to the need for water and sanitation.
Other issues include the problem of dust and sand storms caused by the spread of deserts in Mongolia and China, over a quarter of whose land is classed as desert.
The environmental problems facing small island states, like poverty, natural disasters and declining fish stocks are also on the agenda.
On the eve of the conference the campaign group Friends of the Earth called for Unep to be transformed into the UN Environmental Organisation, with the same membership and funding basis as other UN specialised agencies.
It said this was necessary because of "the rapid deterioration of the world's water resources, urban environments, oceans, forests and other ecosystems, and a too weak and ineffective system of international environmental governance".