So, the lines are drawn. As the industrialized nations of the Group of 8 gather in Heiligendamm, the forces mustered to fight global warming have divided into competing camps.

Germany and Britain seek urgent talks on a new climate change treaty, to go into effect when the Kyoto Protocol expires in 2012. They talk of stiff measures to curb carbon emissions and limit the rise in global temperatures to two degrees Celsius over the coming four decades. The United States, offering an initiative of its own, opposes what it considers to be arbitrary targets and timetables.

We shall see how all this unfolds. But while the United States and Europe debate, some basic facts are beyond dispute.

First, the science is clear. The earth's warming is unequivocal; we humans are its principle cause. Everyday brings new evidence, whether it's the latest Greenpeace report on Mount Everest's retreating glaciers or last week's discovery that the Antarctic Ocean can no longer absorb CO². Think of that: the world's largest carbon trap, filled to capacity.

Second, the time for action is now. The cost of not acting, most economists agree, will exceed the costs of acting early, probably by several orders of magnitude. The damage Hurricane Katrina inflicted on New Orleans may or may not have anything to do with global warming, but it's a useful caution nonetheless on the financial and social perils of delay. It's equally evident that we can no longer afford to endlessly parse our options.

Today's solution du jour - the rage for carbon-trading - is but one weapon in our arsenal. New technologies, energy conservation, forestry projects and renewable fuels, as well as private markets, must all be part of a long-term strategy. So must adaptation. After all, mitigation can only go so far.

There's a third fact - as I see it, the most important of all. That's a basic issue of equity - a question of values, ranking among the great moral imperatives of our era.

Global warming affects us all, yet it affects us all differently. Wealthy nations possess the resources and know-how to adapt. An African farmer, losing crops or herds to drought and dust storms, or a Tuvalu islander worried his village might soon be under water, is infinitely more vulnerable. It is a familiar divide: rich-poor, North-South.

Put bluntly, solutions to global warming proposed by developed nations cannot come at the expense of less fortunate neighbors on the planet. How else would we achieve our Millenium Development Goals of halving world poverty, so solemnly laid down at previous G-8 meetings, if the developing world's aspirations for a greater stake in global prosperity are not honored?

A sense of human dimension should govern any issue that we peoples of the world together must face, climate change included. I consider it a duty, an extension of the sacred obligation to protect that is the foundation of the United Nations.

Each day, I walk through the lobby of UN headquarters in New York, where some of the world's most famous photojournalists are currently displaying their work. They capture the faces and voices of people too often unseen and unheard, from all parts of the globe, many of whom live daily in severe hardship made worse by climate change.

Our debates in the Security Council, often dull affairs conducted in opaque diplomatese, occasionally burst astonishingly to life - and for moments become anything but diplomatic. I recall in one discussion in April, when the representative of Namibia spoke out on his perception of the dangers of climate change. "This is no academic exercise," he all but shouted. "It is a matter of life or death for my country."

He told of how the Namib and Kalahari deserts are expanding, destroying farmland and rendering whole regions uninhabitable. This made me think of my own country, Korea, more and more often choked by dust storms swirling across the Yellow Sea from the expanding Gobi Desert. Malaria has spread to areas where it was once unknown, the Namibian representative went on. Species of plants and animals are dying out, in a land famed for its biodiversity. Developing countries like his own are increasingly subject to what he likened to "low-intensity biological or chemical warfare."

These are strong emotions, drawn from life and not imagined. For those in the developed world, it is important to hear, and to act accordingly. This is the message I will deliver over the coming days in Heiligendamm.

It is why I will soon announce a special high-level meeting on climate change, to be held in New York in September before the annual general debate of the UN General Assembly. It is why I recently appointed three special envoys, whose brief is to speak out for the interests and concerns of nations most vulnerable to climate change, home to the vast majority of the world's people.

I welcome President George W. Bush's recent declaration that he, too, will launch an American climate initiative. I urge that this take place within the UN's global framework for discussion, so that our work may be complementary and mutually reinforcing.

But let us remember. A G-8 agreement that is not global in scope can not hope to offer solutions to a global problem. It is time for new thinking, and a new inclusiveness. We can no longer go about our business as usual.