Once every turn around the sun, inhabitants of our battered blue globe gather by the thousands in an assigned place, for a two-week ritual of despair and hope called a climate conference.

It's humanity distilled under a single roof. And never has such a mix come together as in Copenhagen, where up to 34,000 people _ from Eskimos to "talking trees" to CEOs _ will have crowded through the Bella Center before it's over next weekend.

In just 15 years, the annual conferences reviewing the 1992 U.N. climate treaty have grown into assemblies that, perhaps more than any other, encompass the human enterprise.

Where else will you find people talking about coal mines and cow diets alike, holding forth on reef fishing and nuclear fission, pushing micro-insurance and space satellites, seeking solutions in seaweed and solace in the spiritual side of "sustainability," the dogma of the age?

The activist dressed as a polar bear, the protesters disguised as "trees," the throngs in standard garb of faded jeans or sober suits in the noise and bustle of the Bella's main atrium _ all make up a sister-and-brotherhood that convenes yearly to commune, and often bicker, in the language of climate.

And when the bells of churches ring out 350 times this Sunday across Denmark, the brothers and sisters will know what the bells are tolling for: Many environmentalists say carbon dioxide must be reduced to 350 parts per million in the atmosphere.

The conference's job is to build on the climate treaty, to find ways to reduce our civilization's emissions of CO2 and other gases that come from burning fossil fuels, destroying forests, raising cattle, making cement, growing rice and many other activities that feed us, warm us, transport and enrich us.

If we don't cut back, the global-warming gases enveloping the planet, most scientists agree, will transform its climate, its land and its oceans into something very different from what man has relied on for ages.

That reliance runs thick in our blood, whether it's an Arctic native hunting seal on the ice, a farmer sowing wheat in Australia, an insurance actuary calculating risk in Zurich, or a homeowner flipping on lights powered by hydroelectric dams in the American West.

The interests of all those people and many, many more converge each year for the "COP," the treaty's Conference of Parties.

"The complexity of the talks has increased exponentially. You name it, it has been thrown into the climate change pot," said Cambridge University's Joanna DePledge, who as a U.N. expert helped write the 1997 Kyoto Protocol reducing industrialized nations' emissions, the conferences' major achievement so far.