New Figures: More of U.S. at Risk to Sea Level Rise

Washington D.C. - Nearly 4 million people across the United States, from Los Angeles to much of the East Coast, live in homes more prone to flooding from rising seas fueled by global warming, according to a new method of looking at flood risk published in two scientific papers.

The cities that have the most people living within three feet (one meter) of high tide — the projected sea level rise by the year 2100 made by many scientists and computer models — are in Florida, Louisiana, and New York. New York City, often not thought of as a city prone to flooding, has 141,000 people at risk, which is second only to New Orleans' 284,000. The two big Southeast Florida counties, Miami-Dade and Broward, have 312,000 people at risk combined.

All told, 3.7 million people live in homes within three feet of high tide. More than 500 US cities have at least 10 percent of the population at increased risk, the studies said.

"Southeast Florida is definitely the highest density of population that's really on low coastal land that's really most at risk," said lead author Ben Strauss, a scientist at Climate Central. Climate Central is a New Jersey-based group of scientists and journalists who do research about climate change.

The studies look at people who live in homes within three feet of high tide, whereas old studies looked just at elevation above sea level, according to work published Thursday in the peer-reviewed journal Environmental Research and an accompanying report by Climate Central. That's an important distinction because using high tide is more accurate for flooding impacts, said study co-author Jonathan Overpeck, a scientist at the University of Arizona's Institute of the Environment. And when the new way of looking at risk is factored in, the outlook looks worse, Overpeck said.

"It's shocking to see how large the impacts could be, particularly in southern Florida and Louisiana, but much of the coastal U.S. will share in the serious pain," Overpeck said.

And it's not just residents of coastal areas who will be hurt by this, said Sharlene Leurig, a senior manager for the insurance program at Ceres, a Boston-based investment network. Most coastal areas get flood insurance from the federal program and with more flooding, the program will have to spend more and that will come out of all taxpayers' wallets, she said.

Sea level has already risen about 8 inches since 1880 because warmer waters expand, Strauss said. In addition to the basic physics of ever-warming water expanding, scientist say hotter climate will cause some melting of glaciers in Greenland and western Antarctica that would then cause seas to rise even more.

Flooding from Hurricane Irene last year illustrated how vulnerable coastal places such as Manhattan are with a combination of storms and sea level rise, Strauss said.

Using data from the latest census, Climate Central also has developed an interactive system that allows people to check their risk by entering a ZIP code.

Sea level rise experts at the U.S. Geological Survey and the National Oceanic Atmospheric Administration who weren't part of the studies said the results make sense and were done by experts in the field.

"All low elevation places in the many urban areas along the coast will become more vulnerable," said S. Jeffress Williams, scientist emeritus for the USGS, who wasn't part of the studies. He pointed to Boston, New York City, Norfolk, Va., New Orleans, Charleston, S.C., Miami and Washington and its Virginia suburbs. "More people and infrastructure will be at increasing risk of flooding."

Greenland Ice Melt Seen at Lower Temperatures: Study

By Nina Chestney

Greenland - The complete melt of the Greenland ice sheet could occur at lower global temperatures than previously thought, a study in the journal Nature Climate Change showed on Sunday, increasing the threat and severity of a rise in sea level.

Substantial melting of land ice could contribute to long-term sea level rise of several meters, potentially threatening the lives of millions of people.

"Our study shows that a temperature threshold for melting the (ice sheet) exists and that this threshold has been overestimated until now," said scientists at the Potsdam Institute for Climate Impact Research and the Universidad Complutense de Madrid, who used computer simulations of the ice sheet's evolution to predict its future behavior.

A complete ice sheet melt could happen if global temperatures rose between 0.8 and 3.2 degrees Celsius above pre-industrial levels, with a best estimate of 1.6 degrees, the scientists said.

Previous research has suggested the ice sheet could melt in a range of a 1.9 to 5.1 degree temperature rise, with a best estimate of 3.1 degrees.

One-twentieth of the world's ice is in Greenland, which is about a quarter of the size of the United States and about 80 percent of it is covered by the ice sheet. If it all melted it would be equivalent to a 6.4 meter global sea level rise, previous research has shown.

"If the global temperature significantly overshoots the threshold for a long time, the ice will continue melting and not regrow - even if the climate would, after many thousand years, return to its pre-industrial state," said team leader Andrey Ganopolski at the Potsdam Institute for Climate Impact Research.

Today, global warming of 0.8 degrees has already been recorded.

"The more we exceed the threshold, the faster it melts," said Alexander Robinson, lead-author of the study.
If the world takes no action to limit greenhouse gas emissions, the earth could warm by 8 degrees Celsius.
"This would result in one fifth of the ice sheet melting within 500 years and a complete loss in 2,000 years," he said.

"This is not what one would call a rapid collapse. However, compared to what has happened in our planet's history, it is fast. And we might already be approaching the critical threshold.

If temperature rise is limited to 2 degrees Celsius, a complete melt of the ice sheet could happen in 50,000 years, the study found.

Scientists Melt Mystery Over Icecaps and Sea Levels

By David Fogarty

Worldwide - U.S. scientists using satellite data have established a more accurate figure of the amount of annual sea level rise from melting glaciers and ice caps which should aid studies on how quickly coastal areas may flood as global warming gathers pace.

John Wahr of the University of Colorado in Boulder and colleagues, in a study published on Thursday, found that thinning glaciers and icecaps were pushing up sea levels by 1.5 millimeters (0.06 inches) a year, in line with a 1.2 to 1.8 mm range from other studies, some of which forecast sea levels could rise as much as 2 meters (2.2 yards) by 2100.

Sea levels have already risen on average about 18 centimeters since 1900 and rapid global warming will accelerate the pace of the increase, scientists say, threatening coastlines from Vietnam to Florida and forcing low-lying megacities to build costly sea defenses.

To get a better picture of the pace of the melting, Wahr and colleagues used a satellite that measures variations in gravity fields to study changes in the mass of large ice-covered areas. The data covered 2003-2010.

The glaciers and ice caps included those in the Arctic, South America, Asia as well as Greenland and Antarctica.

Globally, the rate of sea level rise has accelerated in recent decades to reach about 3.5 millimeters a year, with more than half coming from thermal expansion of the oceans.

Water expands as it gets warmer.

While the creeping annual increase might seem small, the rate of sea level rise is expected to grow. Yet scientists have struggled to refine estimates given the uncertainty about the future pace of global warming, growth trajectory of greenhouse gas emissions and the rate at which ice caps will melt.
Using satellite data instead of more limited and time-consuming data from ground measurements was crucial, Wahr said in an email to Reuters.

The team found that loss ice from Greenland and Antarctica was pushing up sea levels by just over one millimeter a year, comprising most of the 1.5 mm annual rise.

Glaciers and mountain ice caps elsewhere comprised the rest, at 0.4 mm/yr between 2003-10.

"That's a large number, and represents a lot of melting ice," said Wahr. "But it's at least 30 percent smaller than previous global estimates, none of which have used GRACE," he said, referring to the name of the satellite.

 FASTER MELTING

The United Nations' Climate Panel estimates sea global sea level rise of 18 to 59 centimeters from 1990 to the 2090s. But those numbers do not include melting from polar regions where the vast majority of the world's freshwater is locked away.

Some climate scientists say the rise is more likely to be between and 1 and 2 meters. They point to accelerating melting of the Greenland and West Antarctic icesheets over the past two decades. Both contain enough water to raise global sea levels by about 60 meters.

Other glaciers and mountain icecaps contain enough water to raise sea levels by nearly a meter.
GRACE measured the changes to ice mass over regions greater than 100 square kilometers. The data showed ice-covered areas in Asia, including the Himalayan and Karakoram ranges, was much less than other estimates, meaning the region contributed very little to sea level rise, in part because many glaciers were at freezing high elevations.

Wahr said the study gave a much clearer picture of what was happening to large ice-covered areas globally, particularly in remote parts of the Himalayas.

"There are simply too many glaciers, and most of them too remote to access, to be able to monitor all of them from the ground. There are more than 200,000 glaciers world-wide," he said, adding only a few hundred have been monitored over time spans of several years or more.

"With GRACE, though, we're able to directly monitor the sum total of all ice loss in an entire glacier system or ice cap."

Ongoing monitoring by the satellite should help scientists get a better handle on the pace of ice melting and sea level rise as the planet heats up.

According to the National Oceanic and Atmospheric Administration, all 11 years in the 21st century so far, including 2011, rank among the 13 warmest in the 132-year temperature record.