FACTBOX-Why are the world's top emitters meeting in Tokyo?

By Gillian Murdoch

(Reuters) - Energy and environment ministers from 20 of the world's top greenhouse gas emitting nations are meeting in Japan to discuss climate change, clean energy and sustainable development.

Here are some questions and answers about the G20's fourth meeting focused on tackling climate change, known as the Gleneagles Dialogue.

WHO IS ATTENDING?

-- Energy and environment ministers from the Group of Eight, (Britain, Canada, France, Germany, Italy, Japan, Russia and the United States) and emerging economies such as Brazil, China and India.

-- The World Bank, International Energy Agency and NGOs.

-- Former British prime minister Tony Blair. He initiated the Gleneagles Dialogue in 2005, calling climate change "probably, long-term the single most important issue we face as a global community."

WHAT IS THE G20?

-- A group of 20 energy and environment ministers comprising member nations of the Gleneagles Dialogue. It is different from the G20 grouping of finance ministers and central bank governors.

WHICH COUNTRIES ARE MEMBERS?

-- Australia, Brazil, Britain, Canada, China, France, Germany, India, Indonesia, Iran, Italy, Japan, Mexico, Nigeria, Poland, Russia, South Africa, South Korea, Spain, the United States, and the European Union (represented by Slovenia, which holds the rotating presidency).

WHY ARE THEY IMPORTANT TO THE CLIMATE DEBATE?

-- The G20 emits almost 20 billion tonnes of carbon dioxide, or about 78 percent of global emissions. G8 nations contribute 45 percent of this, other members contribute 33 percent.

-- The U.S. (23 percent) and China (16 percent) are the G20's greatest individual emitters.

WHAT'S ON THE MEETING'S AGENDA?

-- Host Japan is expected to push for a "sectoral approach" to cutting greenhouse gas emissions after 2012.