NASA

The Hawaiian Islands, seen from space, are the most vulnerable to uneven global sea level rise due to melting glaciers and ice sheets.

Melting ice in Greenland, Antarctica and elsewhere will push up seas unevenly around the world, according to a new study that finds some of the highest waters will inundate Honolulu, Hawaii. 

At the poles, sea levels will actually fall because of the way sea, land and ice interact. For example, the sheer mass of water held in ice in Greenland and Antarctica generates a gravitational field that pulls in the surrounding water. As ice there melts, the gravitational pull weakens and the water is redistributed.

In addition, the melting ice on Antarctica and Greenland will lighten the load on the land beneath it, allowing the land to rebound up and the seafloor to drop a corresponding amount.

"Meaning that as the seafloor deepens, there is another component of sea-level fall, ironically, around these piles of ice," Charles Fletcher, a geologist at the University of Hawaii at Manoa, explained to NBC News.

Fletcher was not involved in the new study but is familiar with its findings, particularly the vulnerabilities of Hawaii — and, more broadly, tropical islands in the Pacific Ocean — to global sea-level rise. 

Modelling glacier wastage
The research was co-led by Giorgio Spada, a professor of Earth physics at the University of Urbino in Italy. It is "the first study to examine a regional pattern of sea-level changes using sophisticated model predictions of the wastage of glaciers and ice sheets over the next century," he told NBC News via email.

He and colleagues used the model to investigate sea level under two future scenarios of sea-level rise: a mid-range, likely-to-happen one and one closer to the upper limit of what’s plausible. Under both, maximum sea-level rise is expected at Honolulu, the researchers reported Feb. 13 in the journal Geophysical Research Letters. 

In the mid-range scenario, worst-affected equatorial oceans could see as much as two feet of sea-level rise, when the fact that water expands as it warms is taken into account. Under the high end, the rate of sea-level change in Honolulu will exceed 0.3 inches a year during the second half of this century. 

Sea-level rise will also be greater than average in Western Australia and throughout the atolls and islands in the tropical Pacific Ocean. In Europe, sea levels will rise, but will likely be lower than the global average given the continent’s proximity to Greenland and the dropping sea levels there.

Incomplete picture
But the picture is far from complete, cautioned Fletcher.

"What this paper and other models have not been able to do because, ultimately, it is too chaotic, is to predict what the winds will be doing," he explained. 

For example, enhanced trade winds associated with a phenomenon called the Pacific Decadal Oscillation are pushing the Pacific Ocean surface westward. As a result, annual sea-level rise in Hawaii is currently about half the global average rate of about 0.1 inch a year, while in the western Pacific the rate is more than 0.3 inch a year.

This may, or may not, change with the next phase of the oscillation, noted Fletcher, whose own research recently highlighted how groundwater beneath land rises with sea levels and could breach the surface, causing severe flooding in places such as Honolulu.

"Overall, the (new) paper is one more twig in the bundle of concerns that low-lying coastal cities, and especially Pacific islands, are highly vulnerable to this problem of sea-level rise," he said, adding that "these Pacific islands have contributed almost nothing to the problem of global warming."

Related stories:

• ‘Horrible’ sea level rise of more than 3 feet plausible by 2100, experts say
• Sea level rose 60 percent faster than UN projections, study finds
• Antarctica, Greenland ice definitely melting into sea, and speeding up, experts warn

John Roach is a contributing writer for NBC News. To learn more about him, check out his website. 

Manuel Silvestri / Reuters

In this file photo, tourists take photos of each other in the flooded Saint Mark's square in Venice.

To protect Venice from periodic floods that are increasingly heightened by the double whammy of rising seas levels and sinking land, a team of Italian researchers suggests lifting up the canal-laced city by pumping seawater into the aquifers below it.

Doing so could result in a uniform uplift of about 30 centimeters over a 10-year period of steady, coordinated pumping via a series of 12 wells that circle the city, according to a study reported in the journal Water Resources Research.

The idea isn't entirely new, but until now its applicability was clouded by a limited understanding of Venice's underlying soils.

The researchers overcame this obstacle by combing through seismic data — obtained in the 1980s by an Italian oil and gas company — to create a 3-D reconstruction of the soils.

"This allowed them to confirm the presence of a continuous layer of impermeable clay below which injected water could increase pore pressure," Scott K. Johnson reports for Ars Technica.

Pore pressure corresponds to water between grains of sediment that can bear some of the load. Subsidence occurs when water is pumped out — as occurred in Venice in the mid-1900s — and the grains pack together, causing the land to sink.

In theory, pumping water back into the soils could reverse this trend, but in reality a full recovery isn't possible, notes Ars Technica.

However, the achievable uplift is sufficient to curb some of Venice's periodic flooding.

Importantly, the coordinated injection of the seawater can prevent one side of the city rising up faster than another, which could crumble the infrastructure — buildings, roads, etc. — that the project aims to protect.

While the cost of the undertaking has been estimated at more than $100 million, the raised up land would reduce operating costs for the MOSE flood gate project meant to stop the rising waters from entering the city at all.

And given that tourism generates at least $2 billion a year in Venice, according to National Geographic, that seems like a small price to pay even for a country at the forefront of the European debt crisis.

What's more, if this approach works in Venice, it might also find use in other parts of the world threatened by rising seas, including Shanghai, New York, New Orleans, Miami, Cairo, Amsterdam and Tokyo.

More on Venice and rising seas:

• Rising seas threaten Shanghai, other big cities
• For Venetians, tourism is no Gondola ride
• Experts float new idea to rescue Venice
• Group fears port work will sink Venice
• Venice flooded as Venice's bad weather continues

John Roach is a contributing writer for msnbc.com. To learn more about him, check out his website. For more of our Future of Technology series, watch the featured video below.