Are The Sea Levels Rising

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Are The Sea Levels Rising – North Miami, Florida, is one of the cities on the US East Coast that has experienced sea level rise higher than the global average. Good pictures

Although a recent UN climate report significantly raised its projections for sea-level rise this century, some scientists warn that even those estimates are too conservative. But one thing is certain: predicting future sea level rise is a very tricky task.

Are The Sea Levels Rising

Are The Sea Levels Rising

When scientists from the Intergovernmental Panel on Climate Change (IPCC) sat down to tackle the sea level rise chapter of their new report released last month, they had their work cut out for them.

Sea Level Rise Is Accelerating: Pnas Study

The sea-level projections of the previous report, published in 2007, are the most controversial part: Scientists and the public have accelerated estimates of less than 60 centimeters (almost two feet) by 2100, which the IPCC has acknowledged, but not included. Potential for rapid flow of ice from Greenland or Antarctica into the ocean. That’s clearly significant – those two ice sheets alone hold enough water to raise sea levels by 65 metres, compared to 0.4 meters from all the world’s mountain glaciers. But researchers’ understanding of ice sheets was so uncertain, the IPCC said, that they couldn’t put a number on it. “Some things had to be overlooked,” said Dan Chambers, a sea-level researcher at the University of Texas. “Because of that, the projections were on the low side.”

Today things are much more certain. In its latest report, published on September 27, the IPCC can finally put a number on ice flow from the poles. As a result, sea levels are estimated to rise by 28 to 98 centimeters (more than three feet) by 2100—50 percent more than 2007 projections. “We’ve got enough of a handle on the problem to say there’s a limit to how crazy things are going to go,” said Ted Scambos, chief scientist at the US National Snow and Ice Data Center.

But that doesn’t mean everything about sea level is now understood. Far away. Even bigger questions hang over the fate of the ice sheets, which the IPCC admits could increase recent projections by tens of centimeters. There are smaller factors that researchers have to deal with.

“We all think we are committed to one meter of sea level rise. We don’t know how soon.”

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The ocean does not rise steadily like water poured into a bathtub—instead, there is a splash and a shake in its rise. Weather patterns like El Niño can push tens of thousands of inches of water ashore at a time, as it did in California in 1998. Floods in Australia in late 2010 strangely flooded the continent, displacing enough seawater to lower global sea levels by 7 millimeters in a year. As seas rise, so does the land: land rises where it was once compressed by glaciers, and river deltas sink into compacted sediments. What appears to be sea level rise in one place may actually be the result of land subsidence.

All of this makes figuring out what the oceans are doing today a dauntingly complex task. Their behavior is even more difficult to express. “Predicting the future is very complicated,” notes Chambers. Steve Nerem of the University of Colorado says, “We all think we’re pretty sure about a meter of sea level rise. We don’t know how soon.”

Some facts are well established. Researchers say global sea levels have risen by about 19 centimeters in the past century. And the rate of increase has accelerated. The 20th century average was 1.7 millimeters per year; The average rate has almost doubled since 1993 – about 3.2 millimeters per year. The overall statistics on multi-decadal trends have not changed much since the IPCC’s last report in 2007. The devil, of course, is in the details.

Are The Sea Levels Rising

One problem is to attribute the increase so far. For example, since the 1970s, about 40 to 50 percent of sea-level rise is thought to be due to “thermal expansion”—water taking up more space as it warms; 35 percent by melting glaciers; 5 percent because people extract, use, and dump groundwater into the ocean; And the remaining amount may be due to the melting of ice at the poles. The primary reason this accounting is tricky is the raw data: satellite measurements of sea level go back to 1993, for example, and of the world’s more than 100,000 glaciers, only 17 have melting records of 30 years or more. “We have to make big assumptions,” Chambers says.

What Causes Sea Level To Rise?

Another problem is separating short-term from long-term trends. For example, the rate of sea-level rise has mysteriously slowed over the past decade. The leading theory is that this overturning occurs as heat is absorbed by the deeper, colder parts of the ocean; Cold water doesn’t expand as much when it warms as warm water, so sea level rise will be less, Nerem says. But the recession is not expected to last.

The biggest question remains how fast and how far the polar ice caps will melt. For this, researchers have an important helper: the Gravity Recovery and Climate Experiment (GRACE). Launched in 2002, these two satellites can detect the mass of the land beneath them and thus monitor the changing weight of the ice sheets. “Grace was a game changer,” says Jerry Mill, a climate modeler at the US National Center for Atmospheric Research in Boulder, Colorado. “They were just guessing before that.”

However, even GRACE is not straightforward. Satellites will detect the end result of a combination of effects, including mass change from shifting crust and crust, increased snowfall, and loss of ice from glacier melting or calving. The results are therefore open to interpretation: the 2012 GRACE estimate of Antarctic ice loss is only half of the 2006 best guess.

In Greenland, the rate of ice melt has doubled since the 1990s, and warmer water at the island’s edge has increased the movement of icebergs into the ocean, the researchers noted. There is more snow, but the island as a whole is weakening and this is expected to continue. “For Greenland, we can be pretty sure we know what’s going on.” “All the mechanisms are converging,” says ice modeler Philippe Hybrechts of the Free University of Brussels. Worryingly, the IPCC expects there to be some global threshold — up to 1 degree C, or 4 degrees Celsius above pre-industrial temperatures — above which Greenland will melt irreversibly in hundreds of years. We are 0.85 degrees Celsius warmer.

Ma Climate Change Clearinghouse

The picture in Antarctica is much bleaker: the error bars in the IPCC projections are not even certain that the continent will lose mass by 2100. You can actually get quite a few in a short period of time. The IPCC expects more snow, especially in the east, and much colder snowmelt. But the continent is losing ice from its edges as warmer water causes ice shelves to collapse. The outflow of this ice has the potential to cause the inevitable collapse of the entire West Antarctic Ice Sheet. This could add up to a tenth of a meter to global sea level rise by 2100. “There’s a lot of ice there,” says David Vaughan of the British Antarctic Survey. “If thrown out of balance, Antarctica could easily become the dominant contributor.”

Faced with all these uncertainties, some have taken a different predictive approach. Instead of trying to model the physics behind each process that contributes to sea level rise (from thermal expansion to ice melting), why not look at how sea level responds to temperature over hundreds of years, they argue? These so-called “semi-empirical” models are more than twice as likely as “process-based” models, making 2 meters of sea-level rise possible by 2100 — enough to flood the homes of 187 million people. But the IPCC says it has no confidence in these conclusions. “They’re interesting,” says Chambers, “but I don’t think they should be given as much weight as process-based models.”

Many scientists disagree, including Stefan Ramsdorf of the Potsdam Institute for Climate Research, who works on semi-empirical models. “We have two different approaches that give different results,” Ramsdorff says. “I don’t know who is closer to the truth. But I object to the IPCC choosing one category and rejecting the other. Ramsdorff notes that other reports, including a 2012 assessment by the US National Oceanic and Atmospheric Administration, have pessimistic projections of sea level rise of up to 2 meters by 2100.

Are The Sea Levels Rising

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Is The Rate Of Sea Level Rise Increasing?

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