Mann says the Pacific islands, which are only 4.6 meters above sea level at their highest point, are facing the imminent prospect of flooding, with salt water intrusion destroying fresh water supplies and increased erosion.
Mann, who was part of the IPCC team awarded the Nobel peace prize in 2007, said it had been expected that island nations would have several decades to adapt to rising sea levels, but that evacuation may now be their only option.
His warning comes just weeks after the National Snow and Ice Data Centre in Boulder, Colorado disclosed that sea ice in the Arctic shrank a dramatic 18% this year on the previous record set in 2007 to a record low of 3.41m sq km.
"We know Arctic sea ice is declining faster than the models predict," Mann told the Guardian at the SXSW Eco conference in Austin , Texas . "When you look at the major Greenland and the west Antarctic ice sheets, which are critical from the standpoint of sea level rise, once they begin to melt we really start to see sea level rises accelerate.
"The models have typically predicted that will not happen for decades but the measurements that are coming in tell us it is already happening so once again we are decades ahead of schedule.
" Island nations that have considered the possibility of evacuation at some point, like Tuvalu , may have to be contending those sorts of decisions within the matter of a decade or so."
Suggesting evacuations would accelerate a change in public consciousness around the issue of climate change, he said: "Thousands of years of culture is at risk of disappearing as the populations of vulnerable island states have no place to go.
"For these people, current sea levels are already representative of dangerous anthropogenic interference because they will lose their world far before the rest of us suffer.
"I think it is an example, one of a number, where the impacts are playing out in real time. It is not an abstract prediction about the future or about far off exotic creatures like polar bears. We are talking about people potentially having to evacuate from places like Tuvalu or the Arctic 's Kivalina, another low lying island which is already feeling the detrimental impacts of sea level rise."
Mann, who is one of the primary targets for attacks by "climate deniers," said that there is still uncertainty about the speed of global warming as it is not clear what the impact of feedback mechanisms could be. In particular, he pointed to the release of methane that will come as the permafrost in the arctic melts.
"We know there is methane trapped and as it escapes into the atmosphere it accelerates the warming even further," he said. "But we don't know quite how much of it there is, but there is definitely the potential to lead to even greater warming than the models predict."
Mann said it was not only island states that were feeling the impacts of climate change and warned that the terrible drought and wildfires suffered by the US this year were just the precursor of far worse to come.
"If you look at the US , some of these things are unfolding ahead of schedule and we are already contending with climate change impacts that were once theoretical," he said.
"We predicted decades ago that this might eventually happen. We are watching them unfold and there are very real consequences to our economy and to our environment.
"The climate models tell us that what today are record breaking levels of heat will become a typical summer in a matter of 20-30 years if we carry on with business as usual. Not only will this become the new normal but we will have to change the scale because we will see heat and drought far worse than anything we have seen before."
The silver lining in all the bad news is that while the political system is gridlocked when it comes to confronting climate change, public attitudes are starting to change.
"It is going to take a little while to sink in," says Mann "but there is evidence of a dramatic shift in awareness and the public increasingly recognises climate change is real and if the public becomes convinced of this, they will demand action and they are connecting the dots because we are seeing climate change playing out in a very visible way. More
