They're not saying it will cause violence, but will be an added factor making things even more dangerous. Fights over resources, like water and energy, hunger and extreme weather will all go into the mix to destabilise the world a bit more, says the report by the Nobel Peace Prize-winning Intergovernmental Panel on Climate Change (IPCC). The summary of the report is being finalised this weekend by the panel in Yokohama.

That's a big change from seven years ago, the last time the IPCC addressed how warming affected Earth, said report lead author Chris Field of the Carnegie Institution of Science in California. The summary that political leaders read in early 2007 didn't mention security issues will, he said, because of advances in research.

"There's enough smoke there that we really need to pay attention to this," said Ohio University security and environment professor Geoff Dabelko, one of the lead authors of the report's chapter on security and climate change.

For the past seven years, research in social science has found more links between climate and conflict, study authors say, with the full report referencing hundreds of studies on climate change and conflict.

The US Defense Department earlier this month in its once-every-four-years strategic review, called climate change a "threat multiplier" to go with poverty, political instability and social tensions worldwide. Warming will trigger new problems but also provide countries new opportunities for resources and shipping routes in places such as the melting Arctic, the Pentagon report says.

After the climate panel's 2007 report, UN Secretary-General Ban Ki-moon wrote that along with other causes, the conflict in the Darfur region of western Sudan "began as an ecological crisis, arising at least in part from climate change. "

While the IPCC report this year downplays global warming's role in that particular strife, saying other issues were far more influential, the report's drafts do add that there is "justifiable common concern" that climate change increases the risk of fighting in similar circumstances.

"Climate change will not directly cause conflict, but it will exacerbate issues of poor governance, resource inequality and social unrest," retired US Navy Adm David Titley, now a Pennsylvania State University professor of meteorology, wrote in an email.

"The Arab Spring and Syria are two recent examples." But Titley, who wasn't part of the IPCC report, says "if you are already living in a place affected by violent conflict, I suspect climate change becomes the least of your worries.