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The G20 summit in Canada offers an opportunity for a hard, long look at how green investments are assisting recovery in many countries while generating employment and environmental gains including on climate change.

China, which put around a third of its stimulus package into environmental sectors, has not only seen its GDP rise sharply. The number of people employed in renewable energies such as solar has also climbed to over 1.5 million with 300,000 new workers in 2009 alone.

Spain's unemployment rates are high, but would undoubtedly be higher without its policy to foster wind power and other clean tech sectors where half a million jobs have been created.

The Republic of Korea has invested well over 80 per cent of its stimulus in areas ranging from sustainable transport and low emission vehicles to energy efficient buildings.

This has now been backed up with a five year green growth plan aimed at cutting carbon dependency and producing 1.8 million jobs.

India's National Rural Employment Guarantee Act is assisting to repair and restore a range of rural infrastructure, critical for livelihoods of the poor, including water storage networks in some of the poorest parts of the country such as Andra Pradesh.

It is delivering improved water security; a 25 per cent increase in wages for agricultural workers and more than 3.5 billion days of work reaching on average 30 million families per year for the programme as a whole.

The State of Sao Paulo is embarking on a Green Economy strategy covering transport to greener buildings. The city represents around a third of Brazil's economy.

While a transition to a low carbon, resource efficient Green Economy is gaining traction globally, some are claiming it is just a developed or rapidly emerging country agenda.

Poorer economies have far more pressing matters to be diverted by such a nouveau notion. Others skirt the debate claiming it is either a glossy repackaging of the sustainable development agenda or worse, a plot to constrain rather than liberate growth developing and least developed economies.

None of this could be further from the truth. In advance of the G20, we have assembled some key case studies - part of a major Green Economy report to be published later in the year.

Kenya - its new green energy policy, including a Feed-In Tariff and 15 year power purchase agreement, is catalyzing an initial target of 500MW of geothermal, wind and sugar wastes-into-energy systems: a rise in the country's installed capacity of over 40 per cent.

Uganda - policies to promote organic agriculture have generated 200,000 certified farmers and exports growing from close to $4 million in 2003 to nearly $23 million now.

Over the past two years, the Green Economy has gone from theory into practice. It is now one of the two major themes as governments prepare for the Rio+20 conference in Brazil in 2012.

The inherent logic offers, perhaps for the first time, a sustainable growth paradigm that is as much a developing country agenda as it is a developed economy one.

New directions, especially ones challenging the status quo and past ways of doing business will always have their critics.

As multiple case studies demonstrate, many developing economies are making their own minds up.

The Green Economy is not a luxury, but a 21st century imperative on a planet of six billion, rising to nine billion people in just 40 years.

The financial and economic crisis has given it wings. How far it will fly will depend on smart policies of national governments - developed and developing alike.

But it will also rest on forward-looking policies by regional development banks; the World Bank, the International Monetary Fund and bilateral development finance of OECD nations.

The G20 summit has the opportunity, if not the responsibility, to enable this transition by taking a leadership role in Toronto, individually and in support of developing economies' aspirations.

A leadership role that re-affirms its commitment to embed sustainability in the global economic recovery; One that recognizes the power of a Green Economy to deliver the opportunity of a fundamentally different and decisive development path across all nations.

Achim Steiner is a UN Under-Secretary General and UNEP Executive Director

Pavan Sukhdev is head of the UNEP Green Economy Initiative on secondment from Deutsche Bank