The findings show that ocean surface temperatures during the Earth's last warm period, around 125,000 years ago, were remarkably similar to what they are today.
What concerns the team, led by researchers at Oregon State University, University College Dublin, the University of Wisconsin and the Science Museum of Virginia, is that at the same time, sea levels were six to nine metres higher than today.
"There's uncertainty in regards to past temperatures in different period of climate history," says Anders Levermann, a professor at the Potsdam Institute for Climate Impact Research who was not part of the research team.
"What makes this study interesting is that they get a new estimate, much lower, of how much the temperature during the last Interglacial was higher than at present. That means that there are a number of implication for example on global sea level rise."
Sea to rise, regardless of temperatures
This is worrying, because it could mean that, even if global temperatures do not rise at all, sea levels will rise drastically, completly changing the face of the earth.
The last time the climate was unusually warm, in the absence of human influence, was about between 116,000 and 129,000 years ago, during what is known as the Last Interglacial Period.
"You have to consider that it takes a long time to raise sea levels by that amount," says Richard Allan, a professor of climate science at the University of Reading. "It takes many hundreds of years to heat up the deep ocean. It also takes thousands of years to melt ice sheets."
The findings also means that some scientific models that have been used to estimate sea levels at various temperatures could have been underestimates.
Hottest year on record ... again
However, temperatures are rising much faster than in the past. Last year was the hottest year ever, marking the third year in a row the record has been broken, with temperatures 1.1 degree Celsius higher than in pre-industrial times, scientists said this week.
While it is true that our planet goes through long periods of warm and cold, these naturally occurring shifts are different from what is happening now with global warning, because now humans are directly affecting the climate.
"If I understand the paper correctly, then during the Last Interglaciation Age the change in temperature took thousands of years," explains Meric Srokosz, an ocean climate scientist at the University of Southampton. "Now we are seeing a similar change in temperature that took only 100 years. This would suggest that we are pushing the climate system with our carbon dioxide emissions."
Fighting climate change is still a key solution to this problem.
"We can still determine how fast and high the seas will actually rise," says Levermann. "There are certain sea levels rise that we can't simple cope with, under which we would have to abandon certain cities along the coast. So it does matter what we do, the urgency of what we have to do is underlined by this report."
No one is completely sure of how fast the sea will be rising in the next decades ... but the clock is ticking. There are more than one billion people living in costal communities that are expected to be swallowed by the sea when these changes occur.