by Michael D. Lemonick, via Climate Central

A new analysis released Thursday in the journal Science implies that the seas could rise dramatically higher over the next few centuries than scientists previously thought — somewhere between 18-to-29 feet above current levels, rather than the 13-to-20 feet they were talking about just a few years ago.

The increase in sea level would largely come from the partial melting of giant ice caps in Greenland and Antarctica, which have remained largely intact since the end of the last ice age, nearly 20,000 years ago. But rising global temperatures, thanks to human greenhouse-gas emissions, have already begun to melt that ancient ice, sending sea level up 8 inches since 1880 alone, with as much as 6 feet or so of additional increase projected by 2100.

That’s not enough to inundate major population centers by itself, but coupled with storm surges, it could threaten millions of Americans long before the century ends. Around the world, sea level rise will put trillions in property at risk within the next few decades.

Twenty-nine feet of sea-level rise, by contrast, or even 18, would put hundreds coastal cities around the globe entirely under water, displacing many hundreds of millions of people and destroying untold trillions in property. It would, in short, be a disaster of unimaginable proportions.

The only good news, said the study’s lead author, Andrea Dutton, a geochemist at the University of Florida, in an interview: “This isn’t going to happen overnight.” It takes a long time to melt such huge volumes of ice. But since global temperatures are likely to remain high for centuries once they’ve been ratcheted up, it might be inevitable.

This scary new scenario for Earth’s future comes from deep in the planet’s past. Geologists have long known that about 120,000 years ago, the world emerged from an ice age into a relatively warm interglacial period. Before plunging back into the deep freeze, global temperatures rose to about the level where they are now, or maybe a little warmer, and hovered there for perhaps 20,000 years.

Naturally enough, Earth’s glaciers and ice caps melted back significantly, and the ocean rose — and since this so-called Last InterGlacial (LIG) is the best example we have of what happens in a warmer world, scientist look to that time for an idea of where the planet is heading.

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The bad news is that even modest global warming likely leads to dangerous sea level rise. The worse news is that continuing to do nothing about greenhouse gas emissions leads to levels of warming and sea rise that are unimaginably catastrophic.

Stabilizing at 2C (3.6F) warming leads to 2.5 feet of sea level rise by 2100 and a devastating 8 feet by 2300, a new analysis finds. The figure at the right is long-term sea level rise under scenarios of very aggressive CO2 mitigation (via one of the new studies, Schaeffer et al. in Nature Climate Change).

Stabilizing at 3C (the RCP4.5 scenario, close to 550 ppm CO2 levels) leads to about 3 feet of SLR by 2100 and over 11 feet of SLR by 2300. That would still require a huge amount of clean energy deployment in the coming decades (see here).

Staying near our current greenhouse emissions emissions path — the “reference” case below, which is not the worst-case scenario — still leads to over 40 inches of SLR by 2100 and then seas continue to rise 7 inches or more a decade!

Rate of sea level rise (in mm/year) under various emissions scenarios.

How future generations would adapt to endlessly rising seas at that rate (or higher) is hard to imagine — even if it were not accompanied by many other simultaneous catastrophes, including Dust-Bowlification, ocean acidification, and ever-worsening extreme weather. The time to act is now.

The SLR analysis above is based on a “a semi-empirical approach” using historical data (see RealClimate). It does not factor in the possibility of nonlinear disintegration of the Greenland or West Antarctic ice sheets, which is already occurring.

Below the jump is a Climate Central excerpt on this study and two others that just came out, which suggest sea level rise could be even greater in key parts of coastal America — JR.

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By Erin Gustafson

Today marks the beginning of hurricane season, a six-month period in which most of the United States’ hurricanes and tropical storms occur.  Of course, the east coast of Florida got the party started early this past Memorial Day weekend, hosting tropical storm Beryl with its 10 inches of rain and maximum sustained wind speed of 70 mph, just one in a series of extreme weather events that took place over the holiday weekend. Beryl is especially significant because it is the largest tropical storm to reach land before the official start of hurricane season on June 1^st.

“I hope this is not a sign of things to come,” commented U.S. Senator Bill Nelson, alluding to the nine to fifteen named storms, including four to eight hurricanes, NOAA’s forecasters predict will appear between now and the end of the season on November 30.  Unfortunately for all of us, the future doesn’t look terribly rosy.

As dramatic as NOAA’s hurricane predictions may sound, the agency is saying that they constitute a “near normal” hurricane season which will be less severe than recent years.  Still, it’s worth noting that any hurricane will bring strong winds, heavy rains, and flooding, and it only takes one massive storm to wreak major havoc.

More troubling still is that hurricane and tropical storm-related flooding this year and in the future will be exacerbated by the effects of rising seas.  In the past hundred and fifty years sea levels have risen 8 inches and scientists estimate that they will rise between one and seven feet by the end of the century.  With recent reports of melting ice sheets in Antarctica and rapidly disappearing glaciers due to climate change, and emerging concern about the role of increased use of water previously locked up in underground aquifers, predictions on the high end are becoming increasingly likely.

A four foot rise in sea level could endanger 5 million residents living in 2.6 million homes on $500 billion of residential real estate in the U.S., not to mention 300 energy-producing facilities, airports, thousands of miles of roads and numerous other types of infrastructure, making them increasingly vulnerable to increased storm surges and flooding.

At a Senate Hearing on the “Impacts of Rising Sea Levels on Domestic Infrastructures“ in April, Dr. Ben Strauss of Climate Central warned that rising seas would “raise the launch pad for coastal storm surges,” more than tripling the odds of what used to be “once in a century floods” within the next two decades.

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Some North Carolina GOP legislators want to stop the use of science to plan for the future. They are circulating a bill that would force coastal counties to ignore actual observations and the best science-based projections in planning for future sea level rise.

King Canute thought he had the power to hold back the tide (in the apocryphal legend). These all-too-real lawmakers want to go one better and mandate a formula that projects a sea level rise of at most 12 inches this century, far below what the science now projects.

A state-appointed science panel reviewed the recent literature and reported that a 1-meter (39 inch) rise is likely by 2100. Many coastal studies experts think a level of 5 to 7 feet should be used, since you typically plan for the plausible worst-case scenario, especially with expensive, long-lived infrastructure.

The 2011 report by the National Academy of Science for the U.S. Navy on the national security implications of climate change concluded:

Based on recent peer-reviewed scientific literature, the Department of the Navy should expect roughly 0.4 to 2 meters global average sealevel rise by 2100, with a most likely value of about 0.8 meter. Projections of local sea-level rise could be much larger and should be taken into account for naval planning purposes,

Rob Young, a geology professor at Western Carolina University and a member of the state science panel, pointed out to the North Carolina Coastal Federation (NCCF) that this proposed law stands against the conclusions of “every major science organization on the globe.” Young notes, “Every other state in the country is planning on three-feet of sea level rise or more.” The Charlotte Observer notes:

Maine is preparing for a rise of up to 2 meters by 2100, Delaware 1.5 meters, Louisiana 1 meter and California 1.4 meters. Southeastern Florida projects up to a 2-foot rise by 2060.

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by Peter Lehner, via NRDC’s Switchboard

In a recent PBS documentary, the mayor of Norfolk, Virginia, Paul Fraim, talks about how flooding has become a monthly occurrence in his town, and how global warming and sea level rise are as much a daily issue for him as education and fighting crime. In some parts of Norfolk, streets turn into rivers at high tide. Homes are flooded five out of six years. People lose their carpets, their appliances, their savings. And they can’t afford to move elsewhere.

Sea levels have risen 14 inches in Norfolk since 1930–almost double the global rate. Part of this alarming change is due to the natural sinking of the area’s soggy tidal lands, but part of it is due to the rising sea levels brought about by global warming. Like stranded polar bears in the North Pole, like disappearing island nations in the Pacific, waterlogged Norfolk is yet another symbol of global warming at work. And even though Norfolk is within spitting distance of our nation’s capital, Congress still hasn’t seemed to grasp the seriousness of the situation.

Turning a blind eye to the realities of global warming is a dangerous game. Scientists predict that sea levels will rise anywhere from 7 inches to 78 inches in the next 100 years (depending, in part, on how much we do to curb global warming pollution), which means that in a few generations, nearly five million people who currently live within 4 feet of high tide could be in the same boat as the residents of Norfolk.

New research shows that global warming will double the chance of a hundred-year flood occurring in many locations within the next 18 years. In some areas, the chance is tripled.

Nearly half the states in the nation will be affected by rising sea levels. Despite these odds, for the most part, we are financially, structurally, and administratively unprepared to deal with the most immediate consequences of global warming.

Bailing out after a flood is a major expense not only for swamped cities, but for taxpayers all over the country. FEMA, the Federal Emergency Management Agency, spent more than $100,000 per home in Norfolk to raise residences above expected water levels. The National Flood Insurance Program (NFIP), run by FEMA, is nearly $18 billion in debt, and has had to borrow money from the Treasury to stay afloat.

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We knew that “deep ocean heat is rapidly melting Antarctic ice.” And we knew that these warm ocean currents melting Antarctica were so intense that, seawater appears to “boil on the surface like a kettle on the stove.”

We also knew that the the West Antarctic ice sheet (WAIS) is inherently far less stable than the Greenland ice sheet because most of it is grounded far below sea level (see below). And JPL has told us that polar ice sheet mass loss is speeding up and is on pace for 1 foot sea level rise by 2050.

Now a new study using NASA satellite data finds the WAIS in particular is “being eaten away from below by warm water” as the AP put it, which “suggests that future sea levels could rise faster than many scientists have been predicting.”

The Nature study itself, “Antarctic ice-sheet loss driven by basal melting of ice shelves,” concludes:

We find that ocean-driven ice-shelf thinning is in all cases coupled with dynamic thinning of grounded tributary glaciers that together account for about 40% of Antarctic discharge and the majority of Antarctic ice-sheet mass loss. In agreement with recent model predictions, we conclude that it is reduced buttressing from the thinning ice shelves that is driving glacier acceleration and dynamic thinning. This implies that the most profound contemporary changes to the ice sheets and their contribution to sea level rise can be attributed to ocean thermal forcing that is sustained over decades and may already have triggered a period of unstable glacier retreat.

This ought to be doubly worrisome since scientists told us in October that the Greenland Ice Sheet “could undergo a self-amplifying cycle of melting and warming … difficult to halt.”

The new study is behind a firewall, so I’m excerpting the NASA news release below along with a NASA video.

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Ousted Maldives president Mohamed Nasheed, the subject of the new climate documentary “Island President,” told MSNBC’s Andrea Mitchell about the challenge of saving his nation from extinction by the effects of greenhouse pollution. “Climate change is a very real issue to the Maldives. It’s not something in the future. We already have 16 islands where we have to relocate people.” The entire nation lies below 1.5 meters above sea level. By 2100, sea levels are likely to rise by at least that amount unless immediate action is taken to reduce the amount of fossil-fuel pollution in the atmosphere. “What happens to the Maldives today will definitely happen the same to everyone else,” Nasheed said. “Maldives today, Manhattan tomorrow,” Mitchell agreed.

“The Island President” opens this weekend in New York City, San Francisco, and Los Angeles, and next week in Washington DC and San Diego.

Rising Sea Levels Threaten Millions by Boosting Storm Surges

This map shows the odds of floods at least as high as historic once-a-century levels, occurring by 2030, based on Climate Central research. The two bars extending from each study point contrast odds estimates incorporating past and projected sea level rise from global warming (red bars), and odds estimates not incorporating this rise (blue bars). Global average sea level has increased more than eight inches since 1880, and the rise is accelerating. Most or all of the rise can be attributed to global warming, which warms and expands global oceans, and causes glaciers and ice sheets to decay.

A Climate Central repost, study here, interactive map here

Sea level rise due to global warming has already doubled the annual risk of coastal flooding of historic proportions across widespread areas of the United States, according to a new report from Climate Central. By 2030, many locations are likely to see storm surges combining with sea level rise to raise waters at least 4 feet above the local high-tide line. Nearly 5 million U.S. residents live in 2.6 million homes on land below this level. More than 6 million people live on land below 5 feet; by 2050, the study projects that widespread areas will experience coastal floods exceeding this higher level.

Titled “Surging Seas,” the report is the first to analyze how sea level rise caused by global warming is compounding the risk from storm surges throughout the coastal contiguous U.S. It is also first to generate local and national estimates of the land, housing and population in vulnerable low-lying areas, and associate this information with flood risk timelines. The Surging Seas website includes a searchable, interactive online map that zooms down to neighborhood level, and shows risk zones and statistics for 3,000 coastal towns, cities, counties and states affected up to 10 feet above the high tide line.

In 285 municipalities, more than half the population lives below the 4-foot mark. One hundred and six of these places are in Florida, 65 are in Louisiana, and ten or more are in New York (13), New Jersey (22), Maryland(14), Virginia (10) and North Carolina (22). In 676 towns and cities spread across every coastal state in the lower 48 except Maine and Pennsylvania, more than 10% of the population lives below the 4-foot mark.

Tidal gauge records show that the sea has already risen 8 inches globally during the last century, and projections point to a steep acceleration. “Sea level rise is not some distant problem that we can just let our children deal with. The risks are imminent and serious,” said report lead author Dr. Ben Strauss of Climate Central. “Just a small amount of sea level rise, including what we may well see within the next 20 years, can turn yesterday’s manageable flood into tomorrow’s potential disaster. Global warming is already making coastal floods more common and damaging.”

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