The theme chosen by the UN Environment Programme (UNEP), which coordinates the day on 5 June on behalf of the UN system and the peoples of the world, will be 'Your Planet Needs You-UNite to Combat Climate Change'.
It reflects the urgency for nations to agree on a new agreement at the crucial climate convention meeting in Copenhagen some 180 days later in the year, and the links with overcoming poverty and improved management of forests.
The news that Mexico has been chosen to host World Environment Day (WED) 2009 was announced jointly by President Felipe Calderón and Achim Steiner, UNEP's Executive Director at a press conference in Mexico City.
The decision in part reflects the growing practical and political role of the Latin American country in the fight against climate change, including its growing participation in the carbon markets.
Mexico is also a leading partner in UNEP's Billion Tree Campaign. The country, with the support of its President and people, has spearheaded the pledging and planting of some 25 per cent of the trees under the campaign.
UNEP has now launched a new and more ambitious phase-the Seven Billion Tree Campaign.
This aims to see more than one new tree planted for every person alive by the Copenhagen meeting as one empowering symbol of the global publics' desire for action by their political leaders on the greatest challenge for this generation.
President Calderón said:'It is great news that today the un, through achim steiner, has announced that Mexico will be the international seat for World Environment Day next 5 june here in our beloved country'.
He said he hoped WED would not only be a time of reflection on the great challenges facing humanity including climate change, but an event linked with 'a lot of action and committment'.
'Undoubtedly this decision further underlines Mexico's determination to manage natural resources and deal with the most demanding challenge of the 21st century-climate change,' said President Calderón.
Mr Steiner, who is also a UN Under-Secretary General, said: 'I am delighted that the President and the people of Mexico will be the hosts of WED only some 180 days before governments meet in Copenhagen before the crucial UN climate convention meeting'.
'Mexico is at the cross-roads of the Green Economy politically, physically and practically. Firstly it still has many challenges, from high air pollution in cities and dependence on fossil fuels to land degradation and the need to fight poverty. But Mexico is also emerging as one among a group of developing economies who are bringing much needed leadership to the need for a new, comprehensive and decisive climate treaty,' he said.
Mr Steiner said that in addition Mexico was seizing the opportunities of the carbon markets and had, in just four short years, become second only to Brazil in terms of wind, solar, biogas and other Clean Development Mechanism (CDM) projects in the region.
'Thirdly Mexico's ambitions in terms of combating climate change under its new Special programme-ambitions that include renewable energy to using forests and other nature-based assets as carbon sinks-will send a clear message to countries in the region and the world that Mexico means to be part of the solution,' he noted.
'Finally, Mexico is set to be one of the big economies of the 21st century along with nations like China and India. Thus its ability to encourage the greening of the economy of neighboring nations-both North and South of its borders-will be significant,' he noted.