A group of researchers has used satellite data from last 25 years to show the rapid rate of sea level increase and how bad it might get by the end of this century.

Thanks to melting ice sheets in Antarctica and Greenland, sea levels have witnessed a rise over past decade or so. The changes are evident and many, including International Panel on Climate Change, have predicted that global levels will rise to 20 inches or more by the end this century.

Now, a new study published in PNAS from the University of Colorado Boulder, builds on that projection and highlights that sea levels are not only rising at a steady pace but accelerating too – at 0.8mm every year.

Currently, sea level is pegged to be increasing at 3mm per year, but if we look at last 25 years, there has been a surge in this rise every year. At this rate, the levels could go up to 10mm per year by 2100.

This means that global sea levels projected for the end of the century would be 26 inches or even more, the exact double of what it could have been if the rate of increase would have been steady. The scientists, who used last 25 years of satellite data to make this observation, say the acceleration in sea level increase can be seen as something similar to a "driver merging onto a highway".

That, as the study says, would be bad enough to flood major coastal cities around the globe. "This is almost certainly a conservative estimate," said lead author Steve Nerem, noting that their estimate does not include any unforeseeable factors that could bring a major change in sea level.

"Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years". However, Nerem adds "given the large changes we are seeing in the ice sheets today, that's not likely" and the acceleration will increase as Earth continues to heat up and ice sheets melt.