In this 2011 photo provided by researcher Hamish Pritchard, summer clouds swirl around the Staccato Peaks of Alexander Island off the Antarctic Peninsula. In a study released Wednesday, June 13, 2018,... (Associated Press) 
 
 In this 2011 photo provided by researcher Hamish Pritchard, summer clouds swirl around the Staccato Peaks of Alexander Island off the Antarctic Peninsula. In a study released Wednesday, June 13, 2018, an international team of ice experts said the melting of Antarctica is accelerating at an alarming... (Associated Press) 
 
 WASHINGTON (AP) — The melting of Antarctica is accelerating at an alarming rate, with about 3 trillion tons of ice disappearing since 1992, an international team of ice experts said in a new study. 
 
 In the last quarter century, the southern-most continent's ice sheet — a key indicator of climate change — melted into enough water to cover Texas to a depth of nearly 13 feet (4 meters), scientists calculated. All that water made global oceans rise about three-tenths of an inch (7.6 millimeters). 
 
 From 1992 to 2011, Antarctica lost nearly 84 billion tons of ice a year (76 billion metric tons). From 2012 to 2017, the melt rate increased to more than 241 billion tons a year (219 billion metric tons), according to the study Wednesday in the journal Nature . 
 
 "I think we should be worried. That doesn't mean we should be desperate," said University of California Irvine's Isabella Velicogna, one of 88 co-authors. "Things are happening. They are happening faster than we expected." 
 
 Part of West Antarctica, where most of the melting occurred, "is in a state of collapse," said co-author Ian Joughin of the University of Washington. 
 
 The study is the second of assessments planned every several years by a team of scientists working with NASA and the European Space Agency. Their mission is to produce the most comprehensive look at what's happening to the world's vulnerable ice sheets in Antarctica and Greenland. 
 
 Outside experts praised the work as authoritative. 
 
 Unlike single-measurement studies, this team looks at ice loss in 24 different ways using 10 to 15 satellites, as well as ground and air measurements and computer simulations, said lead author Andrew Shepherd of the University of Leeds in England. 
 
 It's possible that Antarctica alone can add about half a foot (16 centimeters) to sea level rise by the end of the century, Shepherd said. Seas also rise from melting land glaciers elsewhere, Greenland's dwindling ice sheet and the fact that warmer water expands. 
 
 "Under natural conditions we don't expect the ice sheet to lose ice at all," Shepherd said. "There are no other plausible signals to be driving this other than climate change." 
 
 Shepherd cautioned that this is not a formal study that determines human fingerprints on climate events. 
 
 Forces "that are driving these changes are not going to get any better in a warming climate," said University of Colorado ice scientist Waleed Abdalati, a former NASA chief scientist who wasn't part of the study team. 
 
 In Antarctica, it's mostly warmer water causing the melt. The water nibbles at the floating edges of ice sheets from below. Warming of the southern ocean is connected to shifting winds, which are connected to global warming from the burning of coal, oil and natural gas, Shepherd said. 
 
 More than 70 percent of the recent melt is in West Antarctica. 
 
 The latest figures show East Antarctica is losing relatively little ice a year — about 31 tons (28 metric tons) — since 2012. It was gaining ice before 2012. 
 
 So far scientists are not comfortable saying the trend in East Antarctica will continue. It is likely natural variability, not climate change, and East Antarctica is probably going to be stable for a couple decades, said study co-author Joughin. 
 
 Another study in Nature on Wednesday found that East Antarctic ice sheet didn't retreat significantly 2 million to 5 million years ago when heat-trapping carbon dioxide levels were similar to what they are now. 
 
 Twila Moon, a research scientist at the National Snow and Ice Data Center who wasn't part of the studies, said "ice-speaking, the situation is dire." 
 
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 Follow Seth Borenstein on Twitter: @borenbears . His work can be found here . 
 
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 The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute's Department of Science Education. The AP is solely responsible for all content. ||||| The ice front of Venable Ice Shelf, West Antarctica. (AFP photo/NASA/JPL-Caltech/UC Irvine) 
 
 Late last week, a study published by NASA scientists in the Journal of Glaciology made the surprising claim that the gigantic continent of Antarctica is actually gaining ice, rather than losing it, to the tune of 82 gigatons (or billion metric tons) per year from 2003 to 2008. 
 
 The study has drawn massive amounts of media attention — and no wonder. It contradicts numerous prior scientific claims, including a 2012 study in Science by a small army of polar scientists, a study from earlier this year in Earth and Planetary Science Letters (which found 92 gigatons of net losses per year) and this 2014 study in Geophysical Research Letters (160 gigatons of net losses per year). It also contradicts assertions by the leading consensus body of climate science, the U.N.’s Intergovernmental Panel on Climate Change, which stated in 2013 that Antarctica is “losing mass” and that this process is accelerating. That statement was itself based on multiple studies showing Antarctic ice loss. 
 
 Not only does the new research fly in the face of all of this — if true, it also raises serious questions about our current understanding of sea level rise. If Antarctica is actually gaining ice, that means that a significant percentage of the current rise of the seas, estimated at roughly 3.22 millimeters per year by NASA itself, must be coming from elsewhere. (It takes 360 gigatons of ice to raise seas by 1 millimeter). 
 
 No wonder, then, that a number of researchers have been quoted expressing skepticism about the new research, even as climate change doubters have had a field day — adding the study to an argumentative arsenal that previously included misleading claims about growing Antarctic sea ice. 
 
 So what’s going on here — and what should you make of the new claim that Antarctica isn’t losing ice or raising our seas? 
 
 Measurement disputes and burdens of proof. The new NASA study uses satellite data from NASA’s ICEsat (Ice, Cloud and land Elevation Satellite) and the European Remote-sensing Satellite to derive its results, which are based on precision measurements of the elevation of the ice sheet and how that is changing over time. The key finding is that snow-related mass gain atop the ice sheet is more than compensating for the flow of ice outward in glaciers that reach the sea. 
 
 “Our interpretation is that this has been going on since the beginning of the last ice age when the snowfall over the continent doubled, the accumulation over the continent doubled, as shown in ice cores,” says H. Jay Zwally, the lead author and a longtime NASA expert on the planet’s ice sheets and methods for studying them with satellites. 
 
 More specifically, the research asserts that a “dynamic thickening” of ice over time has occurred as a result of this snowfall. Or as a NASA explanation puts it, “This small thickening, sustained over thousands of years and spread over the vast expanse of these sectors of Antarctica, corresponds to a very large gain of ice – enough to outweigh the losses from fast-flowing glaciers in other parts of the continent and reduce global sea level rise.” 
 
 However, this contradicts many other results, including those derived using a different NASA tool — the GRACE satellites, twin measurement devices that orbit the Earth and measure the changing mass of ice based on differential tugs of gravity on the spacecraft as they pass over it. Accordingly, numerous scientists have expressed skepticism, to varying degrees, about the new research. 
 
 Andrew Shepherd, a glaciologist at the University of Leeds in the UK who was an author of one of the recent studies cited above finding net Antarctic mass loss, puts it this way in an e-mail to the Post: 
 
 Zwally and his team have tried to account for snowfall, which masks changes in the thickness of the polar ice sheets. It’s right to attempt this, but in places where nothing much happens – like the interior of Antarctica, which is a vast desert – it’s really quite difficult to be sure that snowfall can be simulated with enough precision to detect ice imbalance. Fortunately we now have many different ways to examine Earth’s ice sheets – from space and on foot – and I’m confident that we can get to the bottom of this contradiction by taking everything into account. 
 
 I also reached an author of the other study cited above finding a net mass loss using GRACE — geoscientist Christopher Harig of Princeton University. Harig defended the GRACE measurements and the finding that Antarctica is losing mass, and said that a key part of the difference between his research and the new study involves how researchers handle something called “glacial isostatic adjustment” or GIA, which refers to the rising of land as the weight of ice has been removed from it since the last ice age. 
 
 As Harig put it by e-mail: 
 
 GRACE gives us the most direct measurement of mass changes that we have currently. This paper, which uses laser altimetry, claims the discrepancy between our results is due to recent GIA model corrections being incorrect, and that GRACE is more sensitive to the error. If we add back the GIA corrections, and compare our results then, their estimates should agree with ours because we measure mass directly. Instead they are still very far away. Arguing that because their results are different, they must be better, is unsustainable. 
 
 Other scientists have also defended the GRACE approach, and criticized the new research. Al Jazeera, for instance, quoted two other top Antarctic researchers — NASA’s Eric Rignot and the National Snow and Ice Data Center’s Ted Scambos — expressing arguably stronger criticisms of the new work than those cited above. Rignot has published some of the most cited work on the rapid retreat and unsettling vulnerability of West Antarctica, and Scambos is an author of a recent study finding that strong winds are wearing down East Antarctica and likely adding 80 gigatons per year to sea level rise — results that pretty clearly trend in a very different direction from the new NASA study. 
 
 So there is plenty of skepticism out there — but at the same time, Zwally fully stands by the new research. “We have a very high confidence in our results,” he says. “We have examined the accuracy of our results quite carefully, we believe they’re accurate, and in the paper we report why they differ from other methods, and provide constructive critiques of why they differ.” 
 
 In an interview, Zwally also reiterated the notion that GRACE is more sensitive to how one treats glacial isostatic adjustment — clearly, a key point of dispute here. 
 
 What’s clear, then, is that we are looking at a significant scientific disagreement — one that turns on different technologies, methodologies, and adjustments. In such a situation, scientists will now need to hash this out and reconcile their understanding of what is happening to the gigantic snowy mass of East Antarctica in particular. 
 
 In the meantime, nonspecialists may understandably feel baffled by the technical details at play here. But here’s where they can be more confident: Since the new results contradict a lot of other findings, they will likely face a major challenge when it comes to convincing the Antarctic research community as a whole. 
 
 That’s no criticism of the scientists behind the new study — it’s simply how science works. And as the process plays out, it’s fair for scientists and outside observers alike to regard the new research as having to overcome a relatively high burden of proof, and to stay skeptical. 
 
 None of which means you should worry any less about Antarctica and sea level rise. In the meantime, the reasons for worry about Antarctica aren’t any less — and particularly when it comes to West Antarctica, a marine based ice sheet that some scientists fear has already begun a process of irreversible collapse. Indeed, a new study released Monday finds that accelerating mass loss in the glaciers of West Antarctica’s Amundsen sea region could undermine the entire ice sheet and set in motion an inevitable, if slow moving, 3.3 meter (or over 10 foot) rise in global sea levels. 
 
 All of the research groups involved here agree that a key part of West Antarctica is losing mass and that, if treated on its own rather than as part of the larger continent, is making a net positive contribution to sea level rise. The new NASA study only covers a period from 1992 to 2008, so it excludes more recent observations that other researchers have made in this area. Nonetheless, it too finds accelerating mass loss in one key part of West Antarctica that includes the closely watched Pine Island and Thwaites glaciers, growing from 60 gigatons per year between 1992 to 2001 to 97 gigatons per year between 2003 and 2008. 
 
 
 
 Undated photo of Thwaites glacier in West Antarctica. (AFP Photo/NASA/handout) 
 
 Zwally is skeptical about some of the more worrying takes on West Antarctic loss, but he certainly doesn’t deny that it’s happening. “There’s no reason to believe that the loss that we see now will not continue for a long time,” he says. “But there’s a serious question about whether it is still accelerating.” 
 
 Research drawing on more recent data, however, does suggest the loss rate continues to increase. Another NASA supported study of the Amundsen Sea region alone, published in late 2014, ran from 1992 all the way to 2013, and found that the melt rate had “tripled during the last decade.” 
 
 As for what’s actually happening to sea levels if Antarctica is a net gainer rather than loser of ice, Zwally says he thinks the ice is indeed coming from elsewhere — the possibilities include Greenland, the melting of smaller glaciers around the world, and more ocean heat leading to greater thermal expansion of seawater. 
 
 Any way you look at it, though, the bottom line is that we’re facing ongoing sea level rise — and an increasing mass loss from Antarctica or a decreasing mass gain (as the new study finds) would both make that problem worse. As Jamin Greenbaum, a researcher at the University of Texas at Austin who studies East Antarctica, put it by e-mail: 
 
 Unfortunately, this study doesn’t change the fact that sea level rise has been accelerating since around 1870. Actually, it suggests that Antarctica’s ability to slow that rise is decreasing due to alarming trends in coastal mass loss. For instance, in East Antarctica, Totten Glacier is losing enough mass on its own to balance mass gains in an area larger than Texas. 
 
 All in all, then, the current disagreement helps to underscore that even as humans begin to modify the biggest systems and features of the planet, scientists are still struggling to fully measure and comprehend those changes. 
 
 Until the current debate gets ironed out, then, there are several possible stances you can take, ranging from fully accepting the new study over the prior ones — as many climate change doubters seem to be doing — to dismissing it out of hand. But the most reasonable one is probably to regard these surprising new findings with a fair dose of skepticism — and to continue worrying about ice losses along the Antarctic coasts. 
 
 Read more in Energy & Environment: 
 
 Scientists confirm their fears about West Antarctica — that it’s inherently unstable 
 
 Scientists say illegal pot farming operations are poisoning threatened weasels 
 
 The huge paradox at the heart of how people think about environmental risks 
 
 For more, you can sign up for our weekly newsletter here, and follow us on Twitter here. ||||| Media playback is unsupported on your device Media caption Four things you should know about Antarctica 
 
 Antarctica is shedding ice at an accelerating rate. 
 
 Satellites monitoring the state of the White Continent indicate some 200 billion tonnes a year are now being lost to the ocean as a result of melting. 
 
 This is pushing up global sea levels by 0.6mm annually - a three-fold increase since 2012 when the last such assessment was undertaken. 
 
 Scientists report the new numbers in the journal Nature. 
 
 Governments will need to take account of the information and its accelerating trend as they plan future defences to protect low-lying coastal communities. 
 
 The researchers say the losses are occurring predominantly in the West of the continent, where warm waters are getting under and melting the fronts of glaciers that terminate in the ocean. 
 
 "We can't say when it started - we didn't collect measurements in the sea back then," explained Prof Andrew Shepherd, who leads the Ice sheet Mass Balance Inter-comparison Exercise (Imbie). 
 
 "But what we can say is that it's too warm for Antarctica today. It's about half a degree Celsius warmer than the continent can withstand and it's melting about five metres of ice from its base each year, and that's what's triggering the sea-level contribution that we're seeing," he told BBC News. 
 
 Media playback is unsupported on your device Media caption Andrew Shepherd: "The study incorporates 24 independent satellite assessments" 
 
 Space agencies have been flying satellites over Antarctica since the early 1990s. Europe, in particular, has an unbroken observation record going back to 1992. 
 
 These spacecraft can tell how much ice is present by measuring changes in the height of the ice sheet and the speed at which it moves towards the sea. Specific missions also have the ability to weigh the ice sheet by sensing changes in the pull of gravity as they pass overhead. 
 
 Imbie's job has been to condense all this information into a single narrative that best describes what is happening on the White Continent. 
 
 Glaciologists usually talk of three distinct regions because they behave slightly differently from each other. In West Antarctica, which is dominated by those marine-terminating glaciers, the assessed losses have climbed from 53 billion to 159 billion tonnes per year over the full period from 1992 to 2017. 
 
 On the Antarctic Peninsula, the finger of land that points up to South America, the losses have risen from seven billion to 33 billion tonnes annually. This is largely, say scientists, because the floating ice platforms sitting in front of some glaciers have collapsed, allowing the ice behind to flow faster. 
 
 East Antarctica, the greater part of the continent, is the only region to have shown some growth. Much of this region essentially sits out of the ocean and collects its snows over time and is not subject to the same melting forces seen elsewhere. But the gains are likely quite small, running at about five billion tonnes per year. 
 
 And the Imbie team stresses that the growth cannot counterbalance what is happening in the West and on the Peninsula. Indeed, it is probable that an unusually big dump of snow in the East just before the last assessment in 2012 made Antarctica as a whole look less negative than the reality. 
 
 Globally, sea levels are rising by about 3mm a year. This figure is driven by several factors, including the expansion of the oceans as they warm. But what is clear from the latest Imbie assessment is that Antarctica is becoming a significant player. 
 
 "A three-fold increase now puts Antarctica in the frame as one of the largest contributors to sea-level rise," said Prof Shepherd, who is affiliated to Leeds University, UK. 
 
 "The last time we looked at the polar ice sheets, Greenland was the dominant contributor. That's no longer the case." 
 
 In total, Antarctica has shed some 2.7 trillion tonnes of ice since 1992, corresponding to an increase in global sea level of more than 7.5mm. 
 
 Image copyright ESA Image caption Artwork: European satellites in particular have an unbroken record going back to 1992 
 
 The latest edition of the journal Nature has a number of studies looking at the state of the continent and how it might change in a warming world. 
 
 One of these papers, led by US and German scientists, examines the possible reaction of the bedrock as the great mass of ice above it thins. It should lift up - something scientists call isostatic readjustment. 
 
 New evidence suggests where this process has occurred in the past, it can actually constrain ice losses - as the land rises, it snags on the floating fronts of marine-terminating glaciers. 
 
 "It's like applying the brakes on a bike," said Dr Pippa Whitehouse from Durham University. "Friction on the bottom of the ice, which was floating but has now grounded again, slows everything and changes the whole dynamic upstream. We do think the rebound (in the future) will be fast, but not fast enough to stop the retreat we've kicked off with today's warming. 
 
 "Ocean warming is going to make the ice too thin for this process to help." 
 
 Media playback is unsupported on your device Media caption Pippa Whitehouse: "Push a balloon filled with honey - it rebounds when you remove your hand" 
 
 In Imbie's last assessment, the contribution of Antarctica to global sea-levels was considered to be tracking at the lower end of the projections that computer simulations had made of the possible height of the oceans at the end of the century. The new assessment sees the contribution track the upper end of these projections. 
 
 "At the moment, we have projections going through to 2100, which is sort of on a lifetime of what we can envisage, and actually the sea-level rise we will see is 50/60cm," said Dr Whitehouse. "And that is not only going to impact people who live close to the coast, but actually when we have storms - the repeat time of major storms and flooding events is going to be exacerbated," she told BBC News. 
 
 Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
– Scientists monitoring ice loss in Antarctica have chilling news: The melting rate has accelerated alarmingly and the ice sheet is now shedding more than 200 billion tons a year, according to a study involving 88 scientists published in the journal Nature. The researchers say the rate of ice loss has tripled over the last decade and the melting ice sheets are now pushing up sea levels around the world by around a half-millimeter every year, reports the BBC. Antarctica was losing around 49 billion tons of ice a year in the mid-1990s, which went up to an average 219 billion tons a year between 2012 and 2017, the study found. The researchers, who used satellite data going back more than 25 years, say most of the melting ice comes from the West Antarctic sheet, parts of which are in a "state of collapse"—and modest ice growth in the East Antarctic is nowhere near enough to offset it. "The increasing mass loss that they’re finding is really worrying, particularly looking at the West Antarctic, the area that’s changing most rapidly," University of Waterloo glaciologist Christine Dow tells the Washington Post. "And it’s the area that we’re most worried about, because it’s below sea level." Antarctica has lost a total of around 3 trillion tons of ice since 1992 and will be contributing more and more to sea level rise if the current trend continues, warn researchers, who say climate change is the only plausible explanation for the ice loss. "I think we should be worried. That doesn't mean we should be desperate," says study co-author Isabella Velicogna of the University of California Irvine, per the AP. "Things are happening. They are happening faster than we expected."