BELEM, Brazil, Nov 9 (Reuters) - Every year, the U.N.

climate conference conjures hundreds of headlines on global

efforts to spare the world from climate catastrophe. This year's

begins on Monday in the Brazilian rainforest city of Belem.

But what exactly happens at these annual summits? Here's

what you need to know:

WHAT IS A COP?

The annual conference is known as a COP, which stands for

Conference of the Parties that signed the 1992 U.N. climate

treaty.

The treaty, called the U.N. Framework on Climate Change

Convention (UNFCCC), committed countries to working together to

fight climate change - a problem they acknowledged all countries

faced and was best tackled together.

The treaty also established the principle of "common but

differentiated responsibilities", meaning the rich countries

responsible for most of the planet-warming emissions bear a

greater responsibility in solving the problem.

The rotating presidency, now held by Brazil, sets the summit

agenda and works through the year to rally governments toward

shared action and goals. It then hosts the two-week summit,

drawing global attention to the issue while giving national

leaders a chance to swap ideas and hold one another accountable.

Over the years, the annual summits have become a major hub

of geopolitical and financial discussion - projecting the idea

of a "global village" that welcomes all countries, civil society

groups, businesses and financiers.

WHY SHOULD WE CARE ABOUT COP30 THIS YEAR?

For many, this year's 30th climate summit marks as a

full-circle moment.

Brazil had hosted the Rio Earth Summit where the UNFCCC

treaty was signed 33 years ago. This year, the country insisted

the event would return to its roots in acknowledging the world's

most vulnerable including indigenous groups, with some joining

the talks.

Brazil has asked countries to work on realizing past promises,

such as a COP28 pledges to phase out fossil fuel use, rather

than making new ones. COP30 is also the first to acknowledge

failure in meeting the past goal of preventing warming above 1.5

degrees Celsius.

Brazil opted to hold COP30 in the Amazon city of Belem - hoping

to symbolically underline the importance of world forests that

remain targets for logging and industries including mining,

farming and fossil fuel extraction.

WHO ARE THE MAIN PLAYERS AT THE SUMMIT?

Most national governments send teams to the talks. Often,

countries speak together in groups with similar interests.

Some of the more prominent voices include the Alliance of

Small Island States facing an existential threat from rising

seas, and the G77+China bloc of developing countries.

Also influential are the Africa Group and the BASIC Group

consisting of Brazil, South Africa, India and China.

The U.S., which pledged in January to quit the Paris Treaty on

climate change, has stepped away from its past leadership role.

China, Brazil and others have stepped in to fill the void.

TWO WEEKS SEEMS A LONG TIME - WHAT HAPPENS AT THE SUMMIT?

The sprawling COP campus is often a hive of activity, with

campaigners trying to draw attention to their causes while

corporations lobby policy change and seek business deals.

This year has been unique in sloughing off the usual side events

and leaving financiers to meet in Sao Paulo while local leaders

huddled in Rio de Janeiro. Those events, along with a meeting of

world leaders in Belem, were staged before the November 10-21

COP30 in hopes of generating support and momentum for climate

action for the actual talks.

During the summit's first week, country negotiators will lay

out their priorities and gauge one another's positions. Themes

should begin to emerge, while countries and companies announce

action plans and pledges of financing for projects.

Negotiators are typically joined by national ministers

during the second week, to haggle over final decisions including

legal and technical details.

THAT SEEMS EASY, RIGHT?

COPs rarely run smoothly, with countries jockeying for deals

in their national interest and drawing red lines. The talks can

sometimes stall out and lead to acrimony.

Toward the end, negotiators often spend frantic all-night

sessions seeking compromises. Countries then reconvene to

approve decisions - by consensus, not unanimity.

The closing session, when the hammer of a gavel marks the

end of the summit, is almost always delayed - sometimes by

several days. Bring snacks.