LONDON - Uncontrolled greenhouse gas emissions could lead to global warming of 4 degrees centigrade or more by the end of the century, Britain's Meteorological Office said on Monday.

The Met Office launched a new map exploring the impacts on the world if temperatures were allowed to climb to 4 degrees above pre-industrial average temperatures.

If emissions are allowed to continue unchecked, our research shows that they are likely to lead to warming of 4 degrees centigrade or more by the end of the century, said Vicky Pope, head of climate change advice at the Met Office.

This increases the risk of dangerous feedbacks such as the release of methane from melting permafrost that will amplify the warming and lead to irreversible damage to the world's climate and ecosystems.

A United Nations' climate change summit opened on Monday, where world leaders are trying to reach a global agreement which would limit temperature rise to two degrees.

Limiting warming to two degrees would not eradicate the impact of climate change but would limit more dangerous effects, the Met Office said. A rise of four degrees could see cereal crop yields decrease across most major regions in the world, while average sea levels could rise to 80 centimeters

A rise of two degrees would see some crop production increase at mid-to-high latitudes, with negative impacts limited to semi-arid and tropical regions. Sea level rise would be limited to 40 centimeters.

(Reporting by Nina Chestney; Editing by William Hardy)