The UN's expert group, the Intergovernmental Panel on Climate Change (IPCC), published the second part of its broader Fifth Assessment Report on Monday, containing updated climate forecasts and a stronger warning to governments. It assesses the impacts of climate change, and how vulnerable and adaptable human and natural systems are to it.

The latest report warns that rising carbon emissions will increase the risk of conflict, hunger, floods and migration. The impact of climate change, the IPCC said, would increase with every additional degree that temperatures rise.

"Increasing magnitudes of warming increase the likelihood of severe, pervasive, and irreversible impacts," said the report, unveiled in the Japanese city of Yokohama after a five-day meeting.

It says that risks from climate change are "high to very high" if temperatures increase over 4 degrees Celsius above pre-industrial levels, where it believes the world is now heading, with a "disproportionate" risk if there was a rise of 1 to 2 degrees Celsius.

"Impacts from recent climate-related extremes, such as heat waves, droughts, floods, cyclones and wildfires reveal significant vulnerability and exposure of some ecosystems and many human systems to current climate variability," the report said.

Co-author Koko Warner has told DW that politicians need to take decisive action.

"In the past the message has been - we have climate change, it is real, it is established in scientific evidence. So now, society has to adjust. What we are finding, is of course we will adjust," Warner said.

"But there are consequences and tradeoffs. Our decisions or lack of decisions set the trajectory for society - if decision-makers take no decisions, we will still be on a trajectory for certain climate change impacts that we may or may not be able to deal with in society," said Warner.

Global warming could drive conflict

The document builds on previous IPCC forecasts that global temperatures will rise 0.3-4.8 degrees Celsius (0.5-8.6 degrees Fahrenheit) this century, on top of about 0.7 degrees Celsius since the Industrial Revolution. The new report predicts that warming of around 2 degrees Celsius over pre-industrial times could cost between 0.2 and 2.0 percent of global annual income.

"In many cases, we are not prepared for the climate-related risks that we already face," said Vincente Barros, IPCC working group co-chair.

The report says danger could be significantly reduced if greenhouse gas emissions were to be cut swiftly, but countries would nonetheless have to act to make their public utilities more climate resilient. It suggests reducing water wastage, creating more parks, and preventing people from settling in areas prone to extreme weather events.

The IPCC says that climate change could drive conflict and unrest due to migration from areas that become uninhabitable. Poor, tropical nations would be hit harder than wealthier countries in more temperate areas.

A third stage of the IPCC's fifth overall assessment since its formation in 1998 is due to be released in Berlin in April. It will focus on mitigation of climate change. Last September, an IPCC report put the blame on humans for global warming, saying it had led to a faster-than-predicted rise in sea levels.

jr/msh (dpa, AFP, AP)