Speaking before a group of top officials from over 150 nations, including 80 heads of State or Government, Ban said, 'I am convinced that climate change, and what we do about it, will define us, our era, and ultimately the global legacy we leave for future generations.'
'We hold the future in our hands,' he said. 'Together, we must ensure that our grandchildren will not have to ask why we failed to do the right thing, and let them suffer the consequences.'
He cited the findings of the UN Intergovernmental Panel on Climate Change (IPCC) that global warming is directly linked to human activity, calling on the attendees to take 'unprecedented action' to meet this challenge.
'We must be guided by the reality that inaction now will prove the costliest action of all in the long term,' he said.
Development is seriously impeded by climate change, which threatens to reverse the gains made towards the achievement of the Millennium Development Goals (MDGs), eight targets to slash a host of ills including poverty by 2015, the Secretary-General noted.
'But it is not a zero-sum game,' he said.
Economic growth and emissions reductions can take place in parallel, he added, and combating climate change opens the door to opportunities for promoting sustainable development; creations of cleaner technologies, industries and jobs; and the integration of risks brought about by climate change into national policies and practices.
Ban called on industrialized nations to take the lead in halting climate change. Not only do their emissions continue to rise, but their 'support for adaptation by poor countries has fallen well short of what is required.'
He has also invited Delhi's Mayor Arti Mehra and California Governor Arnold Schwarzenegger to brief the landmark meeting's participants on state and local government initiatives to halt global warming.
'All sectors will need to be engaged if global emissions are to peak in the next 10 to 15 years, and be significantly reduced in the years thereafter, as indicated by the IPCC,' he said.
Despite the importance of national action, climate change must be confronted within a global framework, 'one that guarantees the highest level of international cooperation,' the UN Chief stated.
This framework must include bolstered leadership by industrialized countries on emissions reductions; the provision of incentives for action by developing countries without sacrificing their economic growth or poverty reduction efforts; and increasing support for adaptation in developing countries, especially developed and small island developing States.
He voiced hope that today's event - entitled 'The Future in our Hands: Addressing the Leadership Challenge of Climate Change' - will create global momentum for the major summit in Bali, Indonesia, this December.
That meeting seeks to determine future action on mitigation, adaptation, the global carbon market and financing responses to climate change for the period after the expiration of the Kyoto Protocol - the current global framework for reducing greenhouse gas emissions - in 2012.
'Our immediate challenge is to transform our common concern into a new consensus on the way forward,' he said. 'This journey begins in Bali this December. It will succeed or fail based on the strength of the leadership and commitment displayed by the people in this hall.'
Following opening remarks by Ban and other officials, four simultaneous plenary sessions on addressing the challenges of climate change on all fronts will be held on four themes: adaptation, mitigation, technology and financing.
Each session will be chaired by two heads of State, and speakers include world leaders and other delegation heads, as well as representatives of civil society and the private sector.