Menus Subscribe Search

Follow us


Space Probe to Measure How Sloshed Mother Earth Is

• March 16, 2009 • 4:00 AM

A European satellite scheduled to launch today will provide hard data on rising seas.

What do the fates of the tiny Pacific island nations of Tuvalu, Tonga, Kiribati and the Russian launch of a gleaming new European gravity satellite have in common?

Gravity itself.

Variations in Earth’s gravity field — which is a reflection of how Earth’s mass is distributed around the planet — is as subject to the constant motions of the world’s oceans as it is from massive mountain chains. And in how those seas slosh around the globe lies the fate of some 600 million people living in low-lying nations and coastal areas around the world.

Their futures are linked inextricably to gravity-field data to be gathered by the European Space Agency’s upcoming GOCE mission.

GOCE, the space agency’s one-ton Gravity field and steady-state Ocean Circulation Explorer launched today from Plesetsk in Northern Russia, is the first installment of the agency’s Living Planet Program.

Over some 18 months of its nominal mission, the 340-million-euro ($430 million) satellite will measure the variations of Earth’s gravity field, while doing its best to avoid disturbances caused by traces of Earth’s outer atmosphere.

But GOCE needs to be as close to Earth as possible in order to detect miniscule variations in the planet’s gravity-field signals. That’s why it will use ion thrusters to keep it at a mean orbital altitude of some 260 kilometers, or a bit more than 160 miles. From there, GOCE will make unprecedentedly precise global gravity-field measurements.

Its data will, in turn, be used in conjunction with the ongoing U.S.-German Gravity Recovery And Climate Experiment, or GRACE, mission, which launched in 2002. Both GRACE and GOCE will give climatologists the best overall measurements of global sea level yet.

Previously, such satellites measured sea level locally but not globally. GOCE will achieve global measurements by which to calibrate the local measurements.

Unlike GRACE, GOCE doesn’t have the ability to measure changes in the gravity field over time. But its high resolution snapshots will enable researchers to use gravity field data with an accuracy of up to a centimeter and a resolution down to 100 kilometers.

Researchers will in turn use this data to gain a better understanding of current sea levels and global ocean circulation.

Sea-level rise is already happening, more or less, 10 times as fast now as it was a millenium years ago. Sea level has risen some 20 centimeters since 1880, and by 2100 could top a meter or more. Currently, global sea levels are thought to rise on average about 3 centimeters per decade, or about 1.2 inches. Some areas will rise faster; even now some areas will fall due to differences in ocean temperatures from one region to another.

Meanwhile, 20 percent of the Earth’s surface lies within 100 meters above and below the present mean sea level, including the Maldives islands, the Nile delta, parts of Bangladesh, Africa and Southeast Asia. If the rate of rise doubles or triples in the next couple of decades, these at-risk regions will be more likely to suffer flooding, storm surges, coastal damage or even complete inundation.

“Satellites have been making measurements of sea level the world over now since the early 1990s,” said ESA geophysicist Mark Drinkwater, GOCE’s mission scientist.  “GOCE will provide a highly detailed map of the reference topography in any given location in the world. We can look at the sea-level change rate and say whether the sea level is going up and down locally.”

GOCE’s improved gravity-field knowledge will make the “slopes” of the sea level observable, said GOCE researcher Jakob Flury, a geodesist at Leibniz University in Hannover, Germany.

Such slopes are too small to be detected from the ocean surface itself.  They range on the order of only a meter over hundreds of kilometers. But with GOCE, Flury said, these slopes can be observed with centimeter accuracies and therefore can provide a detailed picture of ocean-current patterns over scales of between hundreds and thousands of kilometers.

GOCE will give climate modelers a precise reference for global mean sea levels through the aid of its prime instrument, a gravity gradiometer; providing such measurements in all spatial directions.

As part of the gradiometer, six onboard accelerometers, operating in pairs spaced 50 centimeters apart, will measure differences in the pull in gravity, between small on-board test masses. These variations represent the signature of earthbound masses such as mountains, valleys, ocean ridges, ice packs, the oceans, as well as large masses from deep within Earth’s own interior.

“Six months after launch,” Drinkwater said, “we will be able to make a global map with a unique view of sea surface height variability. This will tell us how to link measurements of sea-level rise from one side of the Pacific to the other. It’s this height variability that drives ocean circulation. Understanding height variability is critical to improving models for more accurate forecasts of climate change.”

Where all this additional water in the rising seas originates is a subject of debate.

“We don’t really understand all the sources of melting,” said Steve Nerem, an earth scientist at the University of Colorado, Boulder. “A third of the sea-level rise is due to melting of mountain glaciers such as the rapidly melting Alaskan glaciers. A third is due to melting of Antartica and Greenland. And a third is due to thermal expansion caused by absorption of heat into the ocean.”

Researchers know that Greenland and Antarctica are both melting at about the same rate. While GOCE will be able to measure the shape of that ice, it still won’t be able to tell researchers how the ice is changing.

Such ice sheets are the most important in terms of possible catastrophic rises of more than a meter of sea level.

“If you melt ice in Greenland and it runs into the ocean, sea level goes up,” said Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory. “The ice that used to be on Greenland was actually pulling, or gravitationally attracting, the water that was in the ocean near its coast, so the water level next to the coast of Greenland will go down. That’s because the gravity field created by all that frozen water will have actually changed thanks to its disappearance.”

On larger scales, Willis says that ocean flows such as the Gulf Stream and the Antarctic Circumpolar current can also tilt the surface of the ocean in the direction of the prevailing gravity. As a result, GOCE should help oceanographers better understand global ocean circulation.

Willis believes the overriding issue is determining what will ultimately happen to the ice sheets. He notes the Greenland ice sheet and the West Antarctic ice sheet are both big masses of ice that remain over land masses. When these ice sheets’ melt-water runs into the oceans, sea level rises.

Much of the melting Arctic ice, by contrast, is already afloat and thus has no impact on sea-level rise.

“The atmosphere is warming; the ocean is warming; and the ice is already melting in both places,” Willis said. “Most climate scientists would suggest sea-level rises of 2 meters over the next 100 years. That would certainly wipe out Kiribati, whose highest level is 6.5 feet.” And as Willis points out, many Pacific island nations like Kiribati would have a problem with even a foot and a half of sea-level rise.

“GOCE will give us insight into contemporary sea-level change and its variability the world over,” said Drinkwater.  “And it will provide a tool for making more educated decisions about how to plan for the future and how to mitigate the problem of sea-level rise for these low-lying nations.”

Sign up for our free e-newsletter.

Are you on Facebook? Become our fan.

Add our news to your site.

Bruce Dorminey
Bruce Dorminey is an award-winning U.S.-based science journalist and author of Distant Wanderers: The Search for Planets beyond the Solar System. A former Hong Kong bureau chief for Aviation Week and Space Technology and former Paris-based technology correspondent for the Financial Times newspaper, he's covered everything from potato blight to dark energy.

More From Bruce Dorminey

A weekly roundup of the best of Pacific Standard and PSmag.com, delivered straight to your inbox.

Recent Posts

November 24 • 11:36 AM

Feeling—Not Being—Wealthy Cuts Support for Economic Redistribution

Study suggests it’s relative wealth that leads people to oppose taxing the rich and giving to the poor.


November 24 • 10:00 AM

Why Are Patients Drawn to Certain Doctors?

We look for an emotional fit between our physicians and ourselves—and right now, that’s the best we can do.


November 24 • 8:00 AM

Why Do We Elect Corrupt Politicians?

Voters, it seems, are willing to forgive—over and over again—dishonest yet beloved politicians if they think the job is still getting done.



November 24 • 6:00 AM

They Steal Babies, Don’t They?

Ethiopia, the Hague, and the rise and fall of international adoption. An exclusive investigation of internal U.S. State Department documents describing how humanitarian adoptions metastasized into a mini-industry shot through with fraud, becoming a source of income for unscrupulous orphanages, government officials, and shady operators—and was then reined back in through diplomacy, regulation, and a brand-new federal law.


November 24 • 4:00 AM

Nudging Drivers, and Pedestrians, Into Better Behavior

Daniel Pink’s new series, Crowd Control, premieres tonight on the National Geographic Channel.


November 21 • 4:00 PM

Why Are America’s Poorest Toddlers Being Over-Prescribed ADHD Drugs?

Against all medical guidelines, children who are two and three years old are getting diagnosed with ADHD and treated with Adderall and other stimulants. It may be shocking, but it’s perfectly legal.



November 21 • 2:00 PM

The Best Moms Let Mess Happen

That’s the message of a Bounty commercial that reminds this sociologist of Sharon Hays’ work on “the ideology of intensive motherhood.”


November 21 • 12:00 PM

Eating Disorders Are Not Just for Women

Men, like women, are affected by our cultural preoccupation with thinness. And refusing to recognize that only makes things worse.


November 21 • 10:00 AM

Queens of the South

Inside Asheville, North Carolina’s 7th annual Miss Gay Latina pageant.


November 21 • 9:12 AM

‘Shirtstorm’ and Sexism in Science

Following the recent T-shirt controversy, it’s clear that sexism in science persists. But the forces driving the gender gap are still being debated.


November 21 • 8:00 AM

What Makes a Film Successful in 2014?

Domestic box office earnings are no longer a reliable metric.



November 21 • 6:00 AM

What Makes a City Unhappy?

According to the National Bureau of Economic Research, Dana McMahan splits time between two of the country’s unhappiest cities. She set out to explore the causes of the happiness deficits.


November 21 • 5:04 AM

Sufferers of Social Anxiety Disorder, Your Friends Like You

The first study of friends’ perceptions suggest they know something’s off with their pals but like them just the same.


November 21 • 4:00 AM

In 2001 Study, Black Celebrities Judged Harshly in Rape Cases

When accused of rape, black celebrities were viewed more negatively than non-celebrities. The opposite was true of whites.


November 20 • 4:00 PM

Women, Kink, and Sex Addiction: It’s Not Like the Movies

The popular view is that if a woman is into BDSM she’s probably a sex addict, and vice versa. In fact, most kinky women are perfectly happy—and possibly healthier than their vanilla counterparts.


November 20 • 2:00 PM

A Majority of Middle-Class Black Children Will Be Poorer as Adults

The disturbing findings of a new study.


November 20 • 12:00 PM

Standing Up for My Group by Kicking Yours

Members of a minority ethnic group are less likely to express support for gay equality if they believe their own group suffers from discrimination.


November 20 • 10:00 AM

For Juvenile Records, It’s ‘Justice by Geography’

A new study finds an inconsistent patchwork of policies across states for how juvenile records are sealed and expunged.


November 20 • 8:00 AM

Surviving the Secret Childhood Trauma of a Parent’s Drug Addiction

As a young girl, Alana Levinson struggled with the shame of her father’s substance abuse. But when she looked more deeply into the research on children of drug-addicted parents, she realized society’s “conspiracy of silence” was keeping her—and possibly millions of others—from adequately dealing with the experience.



November 20 • 6:00 AM

Extreme Weather, Caused by Climate Change, Is Here. Can Nike Prepare You?

Following the approach we often see from companies marketing products before big storms, Nike focuses on climate change science in the promotion of its latest line of base-layer apparel. Is it a sign that more Americans are taking climate change seriously? Don’t get your hopes up.


November 20 • 5:00 AM

How Old Brains Learn New Tricks

A new study shows that the neural plasticity needed for learning doesn’t vanish as we age—it just moves.


Follow us


Feeling—Not Being—Wealthy Cuts Support for Economic Redistribution

Study suggests it's relative wealth that leads people to oppose taxing the rich and giving to the poor.

Sufferers of Social Anxiety Disorder, Your Friends Like You

The first study of friends' perceptions suggest they know something's off with their pals but like them just the same.

Standing Up for My Group by Kicking Yours

Members of a minority ethnic group are less likely to express support for gay equality if they believe their own group suffers from discrimination.

How Old Brains Learn New Tricks

A new study shows that the neural plasticity needed for learning doesn't vanish as we age—it just moves.

Ethnic Diversity Deflates Market Bubbles

But it's not in the rainbow and sing-along way you'd hope for. We just don't trust outsiders' judgments.

The Big One

One in two United States senators and two in five House members who left office between 1998 and 2004 became lobbyists. November/December 2014

Copyright © 2014 by Pacific Standard and The Miller-McCune Center for Research, Media, and Public Policy. All Rights Reserved.