Waves driven by a cyclone appear in the Elbe estuary near the North Sea close to northern Germany. (Christian Charisius/European Pressphoto Agency) 
 
 A group of scientists says it has now reconstructed the history of the planet’s sea levels arcing back over some 3,000 years — leading it to conclude that the rate of increase experienced in the 20th century was “extremely likely” to have been faster than during nearly the entire period. 
 
 “We can say with 95 percent probability that the 20th-century rise was faster than any of the previous 27 centuries,” said Bob Kopp, a climate scientist at Rutgers University who led the research with nine colleagues from several U.S. and global universities. Kopp said it’s not that seas rose faster before that – they probably didn’t – but merely that the ability to say as much with the same level of confidence declines. 
 
 The study was published Monday in the Proceedings of the National Academy of Sciences. 
 
 Seas rose about 14 centimeters (5.5 inches) from 1900 to 2000, the new study suggests, for a rate of 1.4 millimeters per year. The current rate, according to NASA, is 3.4 millimeters per year, suggesting that sea level rise is still accelerating. 
 
 Oceanographer Josh Willis from NASA's Jet Propulsion Laboratory explains how sea levels have changed over the last two decades. (NASA) 
 
 Unsurprisingly, the study blames the anomalous 20th-century rise on global warming — and not just that. It also calculates that, had humans not been warming the planet, there’s very little chance that seas would have risen so much during the century, finding that instead of a 14 centimeter rise, we would have seen somewhere between a 3 centimeter fall and a 7 centimeter rise. 
 
 [Why the U.S. East Coast could be a major ‘hotspot’ for rising seas] 
 
 The new work is particularly significant because, in effect, the sea level analysis produces a so-called “hockey stick” graph — showing a long and relatively flat sea level “handle” for thousands of years, followed by a “blade” that turns sharply upwards in very recent times. 
 
 The discovery of such patterns itself has a long history, going back to a 1998 study by climate researcher Michael Mann of Penn State University and two colleagues — who found a “hockey stick” graph for the planet’s temperature, rather than for its sea level. Since then the “hockey stick,” in its various incarnations, has come in for voluminous criticism from skeptics and doubters of human-caused climate change — even as multiple scientists have continued to affirm the conclusion that the last 100 years or so are way out of whack with what the planet has seen in the past thousand or more. 
 
 [Why the planet’s ancient past holds a worrying lesson about Antarctica] 
 
 The new research also forecasts that no matter how much carbon dioxide we emit, 21st-century sea level rise will still greatly outstrip what was seen in the 1900s. Nonetheless, choices made today could have a big impact. For a low emissions scenario, it finds that seas might only rise between 24 and 61 centimeters. In contrast, for a high emissions scenario — one that the recent Paris climate accord pledged the world to avert — they could rise as much as 52 to 131 centimeters, or, at the very high end, 4.29 feet. 
 
 However, Kopp notes that the methods used to project these totals may not fully capture what happens over the course of this century. “We have a model that’s calibrated against a period when a certain set of processes, largely thermal expansion and glaciers, were dominant,” he says, “and we’re looking forward to a period when other factors will be dominant.” 
 
 As Kopp’s words acknowledge, the major contributors to sea level rise in the 20th century were the melting of mountain glaciers around the globe and the natural expansion of ocean water as it warms. However, in the 21st century, researchers think that the truly major players in potential sea level rise, the huge ice sheets of Greenland and Antarctica, will come to play a larger role. (Just how large remains unclear.) 
 
 The current study was based on combining a variety of so-called “reconstructions” of past rates of sea level from 24 locations around the world with more recent measurements from 66 global tide gauges. That’s necessary because you can’t just measure sea level change in a single place and get a global picture — over long time periods, factors ranging from whether land is rising or sinking to changes in ocean currents and the gravitational pull of the planet’s ice sheets mean that different regions can see different amounts of sea level rise (or fall). 
 
 One of the sites where past sea levels were reconstructed by scientists is pictured below: 
 
 
 
 Coastal wetland in Newfoundland, Canada, that harbors a record of sea level for the past 2,000 years. (Courtesy of Ben Horton) 
 
 The new study follows in the footsteps of a 2011 study that looked at the ocean and climate records contained in salt marshes in North Carolina to infer the history of sea level rise over the past 2,100 years — research that had many of the same authors. That study, too, found that the recent sea level rise is unprecedented over that time period. 
 
 Mann of Penn State, one originator of the “hockey stick” reference and a co-author on the 2011 study (but not the current one), said by email that he thinks the current work is an “incremental advance” on that prior study, albeit one he agreed with in broad outline 
 
 Mann continued by email: 
 
 The study nonetheless reiterates the conclusion we reached [in 2011] that the acceleration in sea level rise over the past century is unprecedented over at least the past millennium, and that this acceleration is directly related to the spike in surface temperature over the past century (i.e. the “hockey stick”). 
 
 The new paper emerges even as another study, also published Monday in the Proceedings of the National Academy of Sciences, produced very similar 21st-century projections of sea level rise. That paper, led by Matthias Mengel of the Potsdam Institute for Climate Impact Research in Germany, also calculated that with unconstrained emissions, the Earth could see a maximum of some four feet of sea level rise by 2100. But it too acknowledged that the approach “cannot cover processes” like the possible collapse of the oceanfront glaciers of the West Antarctic ice sheet, which, it said, “is hypothesized to be already underway.” 
 
 Such calculations are roughly in line with the 2013 projections of the U.N.’s Intergovernmental Panel on Climate Change for expected sea level rise by 2100, although they rely on a different, more simple type of model than that body used. However, Princeton climate scientist Michael Oppenheimer, who was not involved in the current work but collaborates with Kopp and was his postdoctoral adviser, says that this agreement between approaches still “begs the question of just how much disintegration of the polar ice sheets will contribute to sea level during the 21st century since neither type of model is adequate for capturing this growing and potentially disastrous contribution – and that is ultimately the most important unknown, both with regard to sea level and potentially with respect to the whole field of climate change.” 
 
 Capping a major day for sea level rise news, Kopp also released a report Monday along with Benjamin Strauss of Climate Central and two other researchers, using the current study’s approach to determine that thousands of coastal “nuisance” floods in the United States over the 20th century would not have happened without human-caused global warming. 
 
 Based on just four inches of sea level rise attributed to humans in the 20th century, and another two inches so far in the 21st, Strauss said he “was really surprised to see that there are human fingerprints on thousands of coastal floods that we’ve already had in the United States.” The reason is that such nuisance floods — King Tide flooding in Miami would be a good example — represent what Strauss calls a “threshold” phenomenon, which is caused after sea level rise reaches a certain level. 
 
 “I think these studies really put the human fingerprint on Miami Beach’s hundred-million-dollar saltwater flooding problem, and really a lot of what’s going on in South Florida,” Strauss said. 
 
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 For more, you can sign up for our weekly newsletter here, and follow us on Twitter here. ||||| Skip Ad x Embed x Share Sea level rise is one of the most visible ramifications of global warming and new research published on Monday now shows the startling present-day impacts of global warming-related sea level rise. 
 
 Yana Kibyakova walks through a flooded street that was caused by the combination of the lunar orbit, which caused seasonal high tides, and what many believe is the rising sea levels due to climate change on Sept. 29, 2015 in Miami Beach, Fla. (Photo: Joe Raedle, Getty Images) 
 
 Sea levels rose faster in the past century than during the previous 27 centuries due to man-made global warming, a pair of studies published Monday found. 
 
 "The 20th century rise was extraordinary in the context of the last three millennia — and the rise over the last two decades has been even faster," said Robert Kopp, study lead author and an associate professor at Rutgers University. 
 
 The study, "Temperature-driven global sea-level variability in the Common Era," was published in the peer-reviewed Proceedings of the National Academy of Sciences. 
 
 To reach their conclusions, the scientists compiled a database of geological sea-level indicators from marshes, coral atolls and archaeological sites around the world that spanned the last 3,000 years. 
 
 Global sea levels stayed fairly steady for about 3,000 years. Then, with the Industrial Revolution, global sea levels began to rise, the study said. Scientists say the seas rose 5.5 inches from 1900 to 2000, a significant increase, especially for low-lying coastal areas. 
 
 Oops! Make that 20 centuries of sea level rise in one handy chart, via @Climate Central pic.twitter.com/hmAOm4C41t — Elizabeth Kolbert (@ElizKolbert) February 22, 2016 
 
 The burning of fossil fuels for energy produces heat-trapping greenhouse gases. The warm air cause glaciers and ice sheets in Greenland and Antarctica to melt. Warm water expands, taking up more space than cooler water or ice. Global sea levels have closely mirrored temperature changes over the years. As temperatures go up, so do sea levels. 
 
 
 
 Rising sea levels have already impacted U.S. coastal cities. 
 
 What new sea-level data from the past reveal about our future: Millennia of sea-level change https://t.co/WHOvMODmBJpic.twitter.com/Ls3O1pts75 — Stefan Rahmstorf (@rahmstorf) February 22, 2016 
 
 Parts of Norfolk, Va., Charleston, S.C., and Miami flood at high tides, even when it's not raining, according to the National Oceanic and Atmospheric Administration. Floods from storm surges, magnified by the rise in the sea level, have devastated cities including New Orleans and New York. 
 
 Another study — also published Monday in the Proceedings of the National Academy of Sciences by scientists from Germany, Spain and Columbia University — found that global sea level could increase by roughly one to four feet by 2100, depending on how much carbon dioxide, methane and other gases are released into the atmosphere in the coming decades. 
 
 Fastest sea level rise in 2800 years is happening now & it'll only get worse: https://t.co/kVQyPhjIPbpic.twitter.com/1bMrdEblXu — seth borenstein (@borenbears) February 22, 2016 
 
 Read or Share this story: http://usat.ly/1XJ8cBd ||||| NASA scientists say rising sea levels – a natural consequence of the warming of our planet – are unavoidable and more dangerous than thought. 
 
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 A man swims in the ocean near Oceanside, Calif., Aug. 14, 2015. The world's ocean have risen an average three inches since 1992, and will rise at least 3 feet over the next century or two, say NASA scientists. 
 
 Sea levels around the world have already risen three inches and will rise at least three more feet in the next 100 to 200 years, say scientists. 
 
 Since satellites began measuring ocean levels in 1992, global sea levels have risen by an average of three inches as a result of warming waters and melting ice, with some areas rising more than 9 inches due to natural variation, said NASA scientists at a news conference Wednesday. 
 
 As sea levels continue to rise, low-lying states such as Florida are at risk of disappearing, as are major world cities such as Tokyo and Singapore, new data suggests. 
 
 “Given what we know now about how the ocean expands as it warms and how ice sheets and glaciers are adding water to the seas, it’s pretty certain we are locked into at least 3 feet of sea level rise, and probably more,” said Steve Nerem of the University of Colorado, Boulder, and head of the Sea Level Change Team, in a news release. “But we don't know whether it will happen within a century or somewhat longer.” 
 
 The rise is due to two factors, say scientists. For one, when water heats up, it expands. So when the ocean warms, sea level rises. Secondly, ice melts when exposed to heat, and when ice on land melts and runs into the ocean, sea level rises. 
 
 About one-third of sea level rise is caused by warming ocean water, one-third is due to ice loss from the Greenland and Antarctic ice sheets, and the remaining third comes from melting mountain glaciers, say scientists. They warn that the uncertain fate of the polar ice sheets could change that ratio and produce more rapid sea level jumps in the coming decades. 
 
 How high and how fast? 
 
 According to NASA’s satellite measurements, the Greenland ice sheet, covering 660,000 square miles – nearly the area of Alaska – has shed an average of 303 billion tons of ice per year over the past decade. Over the same period, the Antarctic ice sheet, covering 5.4 million square miles – larger than the United States and India combined – has lost an average of 118 billion tons a year. 
 
 NASA's data reveals that, although the picture is complex, sea levels overall are rising faster than they were 50 years ago, more quickly than expected. 
 
 “People need to understand that the planet is not only changing, it’s changed,” said Tom Wagner, the cryosphere program scientist at NASA Headquarters. 
 
 “If you’re going to put in major infrastructure like a water treatment plant or a power plant in a coastal zone,” said Dr. Wagner, “we have data you can now use to estimate what the impacts are going to be in the next 100 years.” 
 
 The consequence of the worldwide sea level rise is already impacting US coastal regions, most noticeably in Florida. 
 
 “Today, normal spring high tides cause street flooding in sections of Miami, something that didn’t happen regularly just a few decades ago,” said Michael Freilich, the director of NASA’s Earth Science Division said. 
 
 In 2013, the United Nations' Intergovernmental Panel on Climate Change (IPCC) made similar predictions and stated that global sea levels would likely rise between 1 and 3 feet by the end of the century. ||||| This satellite image provided by Nature/Knut Christianson, taken Jan. 9, 2016, shows the Thwaites Glacier and its ice cliff at the terminus of Thwaites Glacier, West Antarctica. A new study points says... (Associated Press) 
 
 This satellite image provided by Nature/Knut Christianson, taken Jan. 9, 2016, shows the Thwaites Glacier and its ice cliff at the terminus of Thwaites Glacier, West Antarctica. A new study points says... (Associated Press) 
 
 WASHINGTON (AP) — Warmer air, less frigid water and gravity may combine to make parts of Antarctica's western ice sheet melt far faster than scientists had thought, raising sea levels much more than expected by the end of the century, according to a new study. 
 
 New physics-based computer simulations forecast dramatic increases in melting in the vulnerable western edge of the continent. In a worst case scenario, that could raise sea level in 2100 by 18 to 34 inches (46 to 86 centimeters) more than an international panel of climate scientists predicted just three years ago. 
 
 And even if the countries of the world control heat-trapping gases at the moderate levels they pledged in Paris last year, it would still mean three to 12 inches (8 to 31 centimeters) higher seas than have been forecast thought, according to a study published Wednesday in the journal Nature. 
 
 By the year 2500, in the worst case scenario, the simulations predict seas 42 feet (13 meters) higher— purely from Antarctic melt. 
 
 "You're remapping the way the planet looks from space with those numbers, not just subtle changes about which neighborhoods are going to be susceptible to storm surge," said study lead author Robert DeConto, a climate scientist at the University of Massachusetts. 
 
 This is all because Antarctica is one of the biggest wild cards when scientists try to assess the effects of man-made climate change in upcoming decades. Scientists were caught by surprise when the western portion of the continent started showing signs of rapid ice loss in the last decade or so. 
 
 The United Nations' Intergovernmental Panel on Climate Change has not forecast much sea level rise from Antarctica — just seven inches (18 centimeters) by 2100 in their last report. For this century, the panel saw water expanding from heat, glacier melt and Greenland ice sheet loss as bigger factors. 
 
 Instead of 7 inches, DeConto's simulations forecast sea level rise from Antarctica's melt alone as 2 to 3 feet (64 to 105 centimeters) in the worst case scenario and 10 to 19 inches (26 to 49 centimeters) if greenhouse gas emissions are moderately controlled. And if the world cracks down more dramatically on heat-trapping gases, Antarctica would essentially not add anything to sea level rise, the study said. 
 
 But those figures are just worldwide averages. In many places on the East Coast, like Boston, it could be 25 percent more than that because of geological conditions, DeConto said. 
 
 "North America has a lot to fear from ice loss from West Antarctica, which is where it all begins," DeConto said. 
 
 While other studies have looked at the effect of warming from water below ice sheets and the air that melts from above, DeConto adds in the effect of pooling water and giant ice cliffs. Those ice cliffs, which can be dozens and even hundreds of feet high, can then collapse from the sheer weight of ice and that hastens glacier and ice sheet retreat, he said. 
 
 Ted Scambos at the University of Colorado, who wasn't part of the new study, said it was plausible and used "a few simple yet under-appreciated factors regarding ice retreat." 
 
 Carnegie Institute climate scientist Chris Field said the study drives home the difference the world can make by controlling its greenhouse gas emissions. It's the difference between rising seas that can be managed and conditions that are "dangerously risky," he said. 
 
 ___ 
 
 Online: 
 
 Nature: http://www.nature.com/nature 
 
 ___ 
 
 Follow Seth Borenstein at http://twitter.com/borenbears and his work can be found at http://bigstory.ap.org/content/seth-borenstein ||||| Lewis Crawford (R) gets some help from wrecker driver Terrance Lezama after his vehicle was stranded by freeway flooding as heavy rains hit Houston, Texas January 9, 2012. 
 
 WASHINGTON For the nearly 5 million people who live along the U.S. coasts from Maine to the Gulf of Mexico and the West Coast, rising seas fueled by global warming have doubled the risk of so-called once-a-century floods, according to a trio of environmental reports released on Wednesday. 
 
 These new reports - one from the non-profit group Climate Central and two others published in the peer-reviewed journal Environmental Research Letters - offer a detailed picture of where the most severe risks are along coastlines of the contiguous 48 states. 
 
 Based on 2010 U.S. Census population data and a fresh analysis of high tide lines by the National Oceanic and Atmospheric Administration, the Climate Central report's findings can be seen online at surgingseas.org 
 
 South Florida may be "indefensible" against floods caused by higher seas and the bigger storm surges that are expected to result, said Ben Strauss, an expert on ecology and evolutionary biology who is chief operating officer of Climate Central. He co-authored the two journal reports and the online report. 
 
 An estimated $30 billion in taxable property is vulnerable in southeast Florida alone, according to a preliminary independent analysis cited in the report. 
 
 In California, some places that have never seen severe floods could be vulnerable to them in the next decade or two, Strauss said. 
 
 Climate scientists maintain that people, businesses and infrastructure in low-lying coastal areas of the contiguous 48 U.S. states are vulnerable to sea level rise, and world sea levels have risen by 8 inches since 1880. 
 
 This rise in the world's seas is caused by the expansion of ocean waters as they warm and by the melting of glaciers and ice sheets, Strauss said. This is due to global warming fueled by the emission of heat-trapping greenhouse gases, he and other climate scientists have said. 
 
 Forecasts for sea level rise this century range from 2 to 7 feet, with most estimates centering around 3 to 4 feet, given a projected rise in global temperature of at least 2 to 3 degrees F (1.1 to 1.6 degrees C), Strauss said. 
 
 VULNERABLE ZONES 
 
 As seas rise, they amplify storm surges, the reports said. 
 
 Global warming will more than double the odds of once-a-century floods by 2030 for more than two-thirds of the 55 coastal locations considered in the analysis, the Climate Central report said. For a majority of the locations, warming triples the odds of century floods. 
 
 By 2030, storm surges combined with rising seas could raise waters to 4 feet or more above high tide lines at many locations, the reports said, noting that 4.9 million people live in 2.6 million homes in this vulnerable zone between the observed high tide and the top of expected flood waters. 
 
 Cities are likely to be hit hardest, Strauss said, with 90 percent of the impact projected to come in areas with extremely dense population. 
 
 In 285 coastal cities and towns, more than half the population lives below the 4-foot mark, the Climate Central report found. Florida has 106 of these at-risk municipalities; Louisiana has 65, New Jersey and North Carolina have 22 each, Maryland has 14, New York has 13 and Virginia has 10. 
 
 Florida is a special case because in addition to rising seas and storm surges, its geology and system of drainage canals pose complex problems. "Basically, south Florida in the long term is indefensible," Strauss said. 
 
 "A lot of the state is built on porous bedrock, bedrock that's like Swiss cheese," he said. "You can't practically build a wall to keep the sea out. The water will come up through the ground." 
 
 To prepare for the future, he said, researchers looked to the past, and compared current flooding patterns to what occurred before sea levels rose 8 inches, starting in 1880. 
 
 "Today's century storm would be a once-in-200- or 300-year event, or rarer if there had been no sea level rise from global warming over the last century," Strauss said. "The point is, we're already in the teeth of this." 
 
 (Editing by Eric Beech)
– It's "extremely likely" that sea levels rose faster in the 20th century than at any other time in the previous 2,700 years "and the rise over the last two decades has been even faster," scientists say. A new study—based on "reconstructions" of past sea levels from 24 areas around the world, plus tide gauges—finds global sea levels were steady for almost three millennia before they began to rise with the Industrial Revolution, reports USA Today. "We can say with 95% probability that the 20th-century rise was faster than any of the previous 27 centuries," the lead author tells the Washington Post. Sea levels rose 5.5 inches from 1900 to 2000, or about 1.4 millimeters per year. NASA puts the current rate at 3.4 millimeters per year. Scientists expect sea levels to rise between 9.5 inches and 2 feet by 2100—if we stick to the climate treaty agreed upon in Paris. But a high emissions scenario could see seas rise by more than 4 feet. Another study in Proceedings of the National Academy of Sciences seconds that finding but notes researchers didn't consider the collapse of glaciers of the West Antarctic ice sheet, which "is hypothesized to be already underway." There's no surprise why: Humans burned fossil fuels, which produced greenhouse gases, which melted glaciers and warmed ocean waters, scientists say. If not for humans, sea levels might not have risen at all and thousands of coastal "nuisance" floods in the US would have been avoided, according to Climate Central. (Some 316 US cities may be partially submerged by 2100.)