I watched them filing into the room — heads of state, presidents and kings and prime ministers, tyrants and democrats and dictators and builders of consensus, men (and a few women) who represented all the teeming billions on the planet. They milled around a little uncertainly because they were there without aides or minders. Heads of government are used to having attendants escorting them and giving them directions; but now they were all together, here in a private room at the Rio convention centre, RioCentro, and they had to find their own seats.

That was my doing. I had insisted they come in by themselves, just the leaders of the world around a single big table. I wanted them to be able to sit down informally. Maybe for an hour or so they could look past their political problems, their national agendas, their opportunism, their mutual suspicions and paranoias, look past the alliances and trading blocs and leftover Cold War animosities to see what was really at stake here, in this summer of 1992, at the Earth Summit in Rio.

Maybe, I thought, maybe they'll see how small the problems that preoccupy them really are compared with what they must now confront.

But I doubted it, even then, as I watched them move through the doors. Heads of nations, like the rest of us, are locked into the boxes of their experience, their pressing preconceptions and — unlike the rest of us — their own sense that what they do is important.

They came in slowly, nodding and smiling. There were 116 of them, more heads of government in one place than on any other occasion in history, at what had been billed in the press, with only minor hyperbole and little contradiction, as "the most important political meeting in world history." Many had come to Rio eagerly. Many had had to be persuaded. I had spent years cajoling and persuading and shaming others to come to this ecological summit; often my efforts had nearly been derailed, sometimes by substantive issues — the developing countries still suspected that "the environment" was another stick the rich had chosen to beat them with — and sometimes by irrelevancies (George Bush didn't want Al Gore to be in the room when he spoke, and it was one of my most piquant private moments when then Canadian prime minister Brian Mulroney, unaware of their antipathy, cheerfully brought the two together in the conference hall). Many of the people in the room were together for the first and only time — Fidel Castro with Bush, Israelis with Iranians and Jordanians, Iraqis with Syrians and Turks, enemy with enemy and rival with rival, rich with poor, developing countries with industrialized ones. National delegations and non-governmental organizations had been meeting for days, hammering out agreements. Now it was the leaders' turn.

Slowly they took their seats at the huge oval table we had constructed specially for them. Oval because . . . well, bringing 116 leaders together in a room poses delicate problems of protocol, as you can imagine. That table was one of the logistical challenges for the conference — you couldn't have anyone appearing to take precedence.

Just the leaders of the world, the UN secretary-general . . . and me.

I had preceded them and sat down, going in even before Secretary-General Boutros Boutros-Ghali, and watched them come in, one by one, deferring to each other (but not really), scrambling not to be left out or be beaten to a seat, in some global version of musical chairs.

Eventually they all found places and sat down, and silence fell in the room. They turned in my direction, waiting for me to speak. For a few seconds — it may have been longer — I said nothing.

I looked at the expectant faces, and then it hit me all at once. What am I doing here? Is this really happening? What am I going to say? I had a sudden flutter of nervousness. I could not help reflecting on the long series of events in my life that had culminated in my presence here and wondering where it would lead — for the world community and also for me personally. For a few fleeting seconds I felt myself what I had once been, a poor boy from rural Manitoba, son of a railway worker devastated by the Depression, his fortunes redeemed only by the war, and here was the world, waiting for me to say something, to lecture to the leaders of the planet. It was of course a defining moment for me, but it was also an important, a crucial, moment historically. After all, we were meeting to consider the very future of our planet.

I spotted the Swedish prime minister — I had a special affinity for the Swedes. I saw Castro, and he smiled — we had joked earlier about the length of his speeches, and I had playfully threatened to call time on him if he went on too long.

"Each of you," I said after the Secretary-General had made his opening remarks, "is preoccupied with issues at home — important issues, sometimes urgent issues. But let me submit to you that none of those will be nearly as important to the future of your people as the issues here. Long after your national concerns are forgotten or have become footnotes in the history books, these issues will be central to humanity. So what you do — or fail to do — here, and when you leave here, is of absolutely central importance to your people-and to the world . . ." I was trying to give them context, trying to make them see that there were issues alive in the world that transcended national frontiers, that couldn't be solved in the context of the old nation-states — the very states that they represented and in some cases incarnated. I went on in this vein for a few moments, but not too long; if there is anything that I think is in character with me, it's that I always quickly move to the practical side of things. Okay, we've had our epiphany, our global togetherness. Now, what do we do about it?