(Also see “Manhattan-Size Ice Island Cracks in Half.”)

The crevasse stretches 19 miles (30 kilometers) long and up to 260 feet (80 meters) wide, as shown in a picture taken by NASA’s Terra satellite in October and featured this week as a NASA Image of the Day.

Snaking across the floating tongue of the Pine Island Glacier in West Antarctica, the crack is expected to create an iceberg 350 square miles (907 square kilometers)—versus 303 square miles (785 square kilometers) for Manhattan, Brooklyn, Queens, Staten Island, and the Bronx combined, according to NASA.

As for when the iceberg might shove off, “that is very difficult to predict,” said oceanographer Eric Rignot of NASA’s Jet Propulsion Laboratory, “but in the coming months for sure.”

Glacier “Contributing Most to Sea Level”

Usually there’s nothing extraordinary about a glacier calving, said glaciologist Ted Scambos of the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.

Glaciers that flow into the sea, like the Pine Island Glacier, go through a normal cycle in which the floating section grows, stresses mount, and an iceberg breaks off, Scambos said.

“That is nothing unusual in most cases.”

But when the pattern deviates, glaciologists take notice. In this case, the crack is forming significantly farther “upstream” than has previously been the case. That “signifies that there are changes in the ice,” he said.

When “that point of rifting starts to climb upstream, generally you see some acceleration of the glacier.” That means that the ice will flow into the ocean at a faster rate, contributing even more to sea level rise.

(Related: “Hundreds of Glaciers Melting Faster in Antarctica.”)

 Such an acceleration is of particular concern at the Pine Island Glacier, because, among Antarctic glaciers, it’s “the one that’s contributing the most to sea level rise.”

In fact, he said, ice flows from that glacier alone account for a quarter to a third of Antarctica’s total contribution to sea level rise.

“It’s moving at about three kilometers [almost two miles] per year,” Scambos said. And, he noted, “it’s been accelerating quite a bit.”

(Pictures: Antarctica Warming.)

Cracking Glacier “Really Important”

As far as sea levels are concerned, changes in the Pine Island Glacier and other West Antarctic glaciers are far more important than shifts among the continent’s other glaciers, such as East Antarctica’s Mertz Glacier—despite Mertz’s much publicized release of a Luxembourg-size iceberg in early 2010.

That’s because the “Luxembourg” iceberg came from a glacial ice tongue that had just been “sitting there,” said oceanographer Doug Martinson of Columbia University’s Lamont-Doherty Earth Observatory.

By contrast, “West Antarctica has ice streams, of which Pine Island is one. Those are fast-flowing streams of ice,” said Martinson, who specializes in polar oceans.

When ice breaks off the Pine Island Glacier, he said, more ice can flow in faster from the mountains above—ice that will eventually wind up contributing to sea level rise.

“This glacier,” NSIDC’s Scambos added, “is really important.”

Source National Geographic

New University of Washington research shows that rising sea surface temperatures in the area of the Pacific Ocean along the equator and near the International Date Line drive atmospheric circulation that has caused some of the largest shifts in Antarctic climate in recent decades.

The warmer water generates rising air that creates a large wave structure in the atmosphere called a Rossby wave train, which brings warmer temperatures to West Antarctica during winter and spring.

Antarctica is somewhat isolated by the vast Southern Ocean, but the new results “show that it is still affected by climate changes elsewhere on the planet,” said Eric Steig, a UW professor of Earth and space sciences and director of the UW Quaternary Research Center.

Steig is the corresponding author of a paper documenting the findings that is being published April 10 in the journal Nature Geoscience. The lead author is Qinghua Ding, a postdoctoral researcher in the UW Quaternary Research Center. Co-authors are David Battisti, a UW atmospheric sciences professor, and Marcel Küttel, a former UW postdoctoral researcher now working in Switzerland.

The scientists used surface and satellite temperature observations to show a strong statistical connection between warmer temperatures in Antarctica, largely brought by westerly winds associated with high pressure over the Amundsen Sea adjacent to West Antarctica, and sea surface temperatures in the central tropical Pacific Ocean.

They found a strong relationship between central Pacific sea-surface readings and Antarctic temperatures during winter months, June through August. Though not as pronounced, the effect also appeared in the spring months of September through November.

The observed circulation changes are in the form of a series of high- and low-pressure cells that follow an arcing path from the tropical Pacific to West Antarctica. That is characteristic of a textbook Rossby wave train pattern, Ding said, and the same pattern is consistently produced in climate models, at least during winter.

Using observed changes in tropical sea surface temperatures, the researchers found they could account for half to all of the observed winter temperature changes in West Antarctica, depending on which observations are used for comparison.

“This is distinct from El Niño,” Steig said. That climate phenomenon, which affects weather patterns worldwide, primarily influences sea-surface temperatures farther east in the Pacific, nearer to South America. It can be, but isn’t always, associated with strong warming in the central Pacific.

Steig noted that the influence of Rossby waves on West Antarctic climate is not a new idea, but this is the first time such waves have been shown to be associated with long-term changes in Antarctic temperature.

The findings also could have implications for understanding the causes behind the thinning of the West Antarctic Ice Sheet, which contains about 10 percent of all the ice in Antarctica.

Steig noted that the westerly winds created by the high pressure over the Amundsen Sea pushes cold water away from the edge of the ice sheet and out into the open ocean. It is then replaced by warmer water from deeper in the ocean, which is melting the seaward edge of the ice sheet from below.

The work was funded by the National Science Foundation.

Source Science Daily

It is natural to be rattled by these observations. There is no immediately obvious reason why the rate of ice loss should not continue to increase. Indeed, the recent observations might presage even faster acceleration, perhaps involving the discharge of a substantial fraction of the 1500 mm of sea-level equivalent still stored in Pine Island Glacier and its neighbours. And we have a serious enough problem even if Pine Island Glacier simply maintains its present rate of loss.

Knowing what they know and what they don’t know, “alarmist” is therefore not a label about which glaciologists need to be embarrassed. But they also know that alarmist projections have a way of turning out to be exaggerated.

Consider the energy-balance models, that describe how the climate responds to changes in radiative forcing. The two first such models, published independently by Mikhail Budyko and William Sellers in 1969, projected that the Earth’s surface temperature would drop to tens of degrees below freezing if the output of the Sun were to decrease by only two percent. That made people sit up, and yielded a flurry of publications showing that there are plenty of ways in which the climate system moderates the severity of the negative feedback which was the basis for the original findings.

Even though they are based on measurement rather than on modelling, might our concerns about the recent behaviour of outlet glaciers in Antarctica and Greenland be similarly exaggerated? In a recent modelling study, Ian Joughin and co-authors suggest that the answer is “Probably, but not necessarily”.

The model is not quite state-of-the-art, in that it does not solve the full Stokes equation but a simpler form of the dynamical system that is appropriate for ice shelves and ice streams. The authors were obliged to handle the grounding line, where the grounded ice stream feeds into the floating ice shelf, somewhat roughly. Nevertheless the calculations allow for careful treatment of the rapid sliding at the base of the ice stream, and the implied very large rates of basal melting. And the model does a good job of reproducing the documented behaviour of Pine Island Glacier up to 2009.

Most of the ice in the Pine Island Glacier catchment is flowing very slowly indeed, at a few metres per year at most. But as it converges on the outlet of the catchment it accelerates spectacularly, and is moving at thousands of metres per year by the time it starts to float at the grounding line. Most of the speed is the result of basal sliding, so the ice stream is not unlike a rigid plug, punching its way through the much slower ice on its flanks. This peculiar setup is the core of the problem.

Joughin and his co-authors simulated responses of the glacier to a variety of scenarios that might or might not represent the next hundred years. Even the more extreme scenarios, featuring basal melting at four times the present rate, did not lead to flotation of the entire 200-kilometre length of the ice stream, as one earlier study had suggested. Nor did the model come anywhere close to an even simpler extrapolation of current behaviour, based on kinematics rather than dynamics.

Don’t breathe out yet, however. The results considered by the authors to be the most probable have Pine Island Glacier continuing to lose mass at rates comparable to the recent rates. It doesn’t continue to accelerate, but it doesn’t slow down either. The grounding line doesn’t continue to migrate inland, but the inland thinning implied by the fast flow does continue.

It would be wrong to write off this heroic but tentative modelling effort, which is an important step towards the goal of understanding Pine Island Glacier. Models like this one, and like the energy-balance models that followed up on Budyko and Sellers, are part of the learning process. They suggest that doomsday isn’t going to happen just yet. But, in short, doomsday scenarios are educational.

Source Environmental research web

Footnote – This situation and the broader picture of the grounding lines under the Pine Island Glacier and the Ross Ice Shelf are cover in the book ZERO Greenhouse Emissions – get the ebook here.

Named by the French in 1792 the Peak stands 262 metres above sea level. At the base of the impressive rock formation, signs point the way to what is described as a two hour round trip to the summit. Being a very hot and humid day and with the suggestion that it should only be attempted by fit hikers, I decided to give the summit climb a miss!

There was another sign at the base that caught my attention. The origins of the rock. Geologists had established that the massive granite formation was formed 120 million years ago; a long time. The sign went on to detail how the cave on the top of Frenchman’s Peak was formed by waves over thousands of years, 40 million years ago during the Middle Eocene period, when sea level was 250 metres higher than today.

Excerpt from SkepticalScience.com

Around 40 million years ago, sea surface temperatures rose around 5°C in a period called the Middle Eocene Climatic Optimum (MECO). A new study Transient Middle Eocene Atmospheric CO₂ and Temperature Variations (Bijl et al 2010) has found atmospheric CO2 was the primary driver of this global warming event. During this period, CO2 levels rose dramatically to 2 to 3 times previous levels. This study gives us further insight into how climate responds to changing CO2 levels and provides evidence for strong climate sensitivity. Read more Skeptical Science article

As you watch the following YouTube videos, it may strike you as it did me that everything viewed from the top of Frenchman’s Peak by these visitors; 40 million years ago was below the sea! A very different world!

With continuing rises in greenhouse emissions Frenchman’s Peak may one day return to its origins.

We are entering a new era, one of rapid and often unpredictable climate change. In fact, the new climate norm is change. The 25 warmest years on record have come since 1980. And the 10 warmest years since global recordkeeping began in 1880 have come since 1998.

The effects of rising temperature are pervasive. Higher temperatures diminish crop yields, melt the mountain glaciers that feed rivers, generate more-destructive storms, increase the severity of flooding, intensify drought, cause more-frequent and destructive wildfires, and alter ecosystems everywhere. We are altering the earth’s climate, setting in motion trends we do not always understand with consequences we cannot anticipate.

Crop-withering heat waves have lowered grain harvests in key food-producing regions in recent years. One with a profoundly direct human impact was the searing heat wave that broke temperature records across Europe in 2003. The intense heat, which contributed to the world grain harvest falling short of consumption by 90 million tons, also claimed more than 52,000 lives.

There has also been a dramatic increase in the land area affected by drought in recent decades. A team of scientists at the National Center for Atmospheric Research reports that the area of the globe experiencing very dry conditions expanded from less than 15 percent in the 1970s to roughly 30 percent by 2002. The scientists attribute part of the change to a rise in temperature and part to reduced precipitation, with high temperatures becoming progressively more important during the latter part of the period. A 2009 report published by the U.S. National Academy of Sciences reinforces these findings. It concludes that if atmospheric CO2 climbs to 450–600 ppm, the world will face irreversible dry-season rainfall reductions in several regions of the world. The study likened the conditions to those of the U.S. Dust Bowl era of the 1930s.

The warming is caused by the accumulation of heat-trapping “greenhouse” gases and other pollutants in the atmosphere. Of the greenhouse gases, CO2 accounts for 63 percent of the recent warming trend, methane 18 percent, and nitrous oxide 6 percent, with several lesser gases accounting for the remaining 13 percent. Carbon dioxide comes mostly from electricity generation, heating, transportation, and industry. In contrast, human-caused methane and nitrous oxide emissions come largely from agriculture—methane from rice paddies and cattle and nitrous oxide from the use of nitrogenous fertilizer.

Atmospheric concentrations of CO2, the principal driver of climate change, have climbed from nearly 280 parts per million (ppm) when the Industrial Revolution began around 1760 to 387 ppm in 2009. The annual rise in atmospheric CO2 level, now one of the world’s most predictable environmental trends, results from emissions on a scale that is overwhelming nature’s capacity to absorb carbon. In 2008, some 7.9 billion tons of carbon were emitted from the burning of fossil fuels and 1.5 billion tons were emitted from deforestation, for a total of 9.4 billion tons. But since nature has been absorbing only about 5 billion tons per year in oceans, soils, and vegetation, nearly half of those emissions stay in the atmosphere, pushing up CO2 levels.

Methane, a potent greenhouse gas, is produced when organic matter is broken down under anaerobic conditions, including the decomposition of plant material in bogs, organic materials in landfills, or forage in a cow’s stomach. Methane can also be released with the thawing of permafrost, the frozen ground underlying the tundra that covers nearly 9 million square miles in the northern latitudes. All together, Arctic soils contain more carbon than currently resides in the atmosphere, which is a worry considering that permafrost is now melting in Alaska, northern Canada, and Siberia, creating lakes and releasing methane. Once they get under way, permafrost melting, the release of methane and CO2, and rising temperature create a self-reinforcing trend, what scientists call a “ positive feedback loop.” The risk is that the release of a massive amount of methane into the atmosphere from melting permafrost could simply overwhelm efforts to stabilize climate.

Another unsettling development is the effect of atmospheric brown clouds (ABCs) consisting of soot particles from burning coal, diesel fuel, or wood. These particles affect climate in three ways. First, by intercepting sunlight, they heat the upper atmosphere. Second, because they also reflect sunlight, they have a dimming effect, lowering the earth’s surface temperature. And third, if particles from these brown clouds are deposited on snow and ice, they darken the surface and accelerate melting. These effects are of particular concern in India and China, where a large ABC over the Tibetan Plateau is contributing to the melting of glaciers that supply the major rivers of Asia. Soot deposition causes earlier seasonal melting of mountain snow in ranges as different as the Himalayas of Asia and the Sierra Nevada of California, and it is also believed to be accelerating the melting of Arctic sea ice.

In contrast to CO2, which may remain in the atmosphere for a century or more, soot particles in ABCs are typically airborne for only a matter of weeks. Thus, once coal-fired power plants are closed or wood cooking stoves are replaced with solar cookers, atmospheric soot disappears rapidly.

If we continue with business as usual, the Intergovernmental Panel on Climate Change’s (IPCC’s) projected rise in the earth’s average temperature of 1.1–6.4 degrees Celsius (2–11 degrees Fahrenheit) during this century seems all too possible. Unfortunately, during the several years since the IPCC study was released, both global CO2 emissions and atmospheric CO2 concentrations have exceeded those in its worst-case scenario. With each passing year the chorus of urgency from the scientific community intensifies. Each new report indicates that we are running out of time. For instance, a landmark 2009 study by a team of scientists from the Massachusetts Institute of Technology concluded that the effects of climate change will be twice as severe as those they projected as recently as six years prior. Instead of a likely global temperature rise of 2.4 degrees Celsius, they now see a rise exceeding 5 degrees.

Another report, this one prepared independently as a background document for the December 2009 international climate negotiations in Copenhagen, indicated that every effort should be made to hold the temperature rise to 2 degrees Celsius above pre-industrial levels. Beyond this, dangerous climate change is considered inevitable. To hold the temperature rise to 2 degrees, the scientists note that CO2 emissions should be reduced by 60–80 percent immediately, but since this is not possible, they note that, “To limit the extent of the overshoot, emissions should peak in the near future.”

The Pew Center on Global Climate Change sponsored an analysis of some 40 scientific studies that link rising temperature with changes in ecosystems. Among the many changes reported are spring arriving nearly two weeks earlier in the United States, tree swallows nesting nine days earlier than they did 40 years ago, and a northward shift of red fox habitat that has it encroaching on the Arctic fox’s range. Inuits have been surprised by the appearance of robins, a bird they have never seen before. Indeed, there is no word in Inuit for “robin.”

Douglas Inkley, National Wildlife Federation senior science advisor, notes, “We face the prospect that the world of wildlife that we now know—and many of the places we have invested decades of work in conserving as refuges and habitats for wildlife—will cease to exist as we know them, unless we change this forecast.” Unfortunately, this observation holds true for humans as well. If we cannot quickly reduce carbon emissions, it is civilization itself that is at risk.

Adapted from Chapter 3, “Climate Change and the Energy Transition,” in Lester R. Brown, Plan B 4.0: Mobilizing to Save Civilization (New York: W.W. Norton & Company, 2009), available online at www.earth-policy.org/books/pb4.

Additional data and information sources at http://www.earth-policy.org/.

Satellite imagery from the European Space Agency shows that a massive iceberg that calved from Greenland’s Petermann Glacier on August 4 has cruised into the Nares Strait, putting 28 kilometers between it and its source.

The 245-square-kilometer iceberg – that’s about four times the size of Manhattan – faces a fractured future. The satellite imagery shows it has hit a small island, which is slowing its journey but also threatening to break it up.

The berg is being tracked by the European Space Agency’s Envisat satellite, using both radar and photographs.

Related stories

Massive Ice Island Breaks off Greenland

Greenland Ice Sheet faces a tipping point in 10 years

The entire ice mass of Greenland will disappear from the world map if temperatures rise by as little as 2C, with severe consequences for the rest of the world, a panel of scientists told Congress today.

Greenland shed its largest chunk of ice in nearly half a century last week, and faces an even grimmer future, according to Richard Alley, a geosciences professor at Pennsylvania State University

“Sometime in the next decade we may pass that tipping point which would put us warmer than temperatures that Greenland can survive,” Alley told a briefing in Congress, adding that a rise in the range of 2C to 7C would mean the obliteration of Greenland’s ice sheet.

The fall-out would be felt thousands of miles away from the Arctic, unleashing a global sea level rise of 23ft (7 metres), Alley warned. Low-lying cities such as New Orleans would vanish.

“What is going on in the Arctic now is the biggest and fastest thing that nature has ever done,” he said.

Speaking by phone, Alley was addressing a briefing held by the House of Representatives committee on energy independence and global warming.

Greenland is losing ice mass at an increasing rate, dumping more icebergs into the ocean because of warming temperatures, he said.

The stark warning was underlined by the momentous break-up of one of Greenland’s largest glaciers last week, which set a 100 sq mile chunk of ice drifting into the North Strait between Greenland and Canada.

The briefing also noted that the last six months had set new temperature records.

Robert Bindschadler, a research scientist at the University of Maryland, told the briefing: “While we don’t believe it is possible to lose an ice sheet within a decade, we do believe it is possible to reach a tipping point in a few decades in which we would lose the ice sheet in a century.”

The ice loss from the Petermann Glacier was the largest such event in nearly 50 years, although there have been regular and smaller “calvings”.

Petermann spawned two smaller breakaways: one of 34 sq miles in 2001 and another of 10 sq miles in 2008.

Andreas Muenchow, professor of ocean science at the University of Delaware, who has been studying the Petermann glacier for several years, said he had been expecting such a break, although he did not anticipate its size.

He also argued that much remains unknown about the interaction between Arctic sea ice, sea level, and temperature rise.

Muenchow told the briefing that over the last seven years he had only received funding to measure ocean temperatures near the Petermann Glacier for a total of three days.

He was also reduced, because of a lack of funding, to paying his own airfare and that of his students to they could join up with a Canadian icebreaker on a joint research project in the Arctic. 

Greenland's Petermann Glacier in 2009. Researchers say a quarter of the ice shelf has broken away.

August 7^th — A piece of ice four times the size of Manhattan island has broken away from an ice shelf in Greenland, according to scientists in the U.S.

The 260 square-kilometer (100 square miles) ice island separated from the Petermann Glacier in northern Greenland early on Thursday, researchers based at the University of Delaware said.

The ice island, which is about half the height of the Empire State Building, is the biggest piece of ice to break away from the Arctic icecap since 1962 and amounts to a quarter of the Petermann 70-kilometer floating ice shelf, according to research leader Andreas Muenchow.

“The freshwater stored in this ice island could keep the Delaware or Hudson rivers flowing for more than two years. It could also keep all U.S. public tap water flowing for 120 days,” Muenchow said.

Muenchow’s team is studying ice in the Nares Strait separating Greenland from Canada, about 1,000 kilometers south of the North Pole.

Satellite data from NASA’s MODIS-Aqua satellite revealed the initial rupture which was confirmed within hours by Trudy Wohlleben of the Canadian Ice Service, according to the University of Delaware website.

Muenchow said the island could block the Nares Strait as it drifts south, or break into smaller islands and continue towards the open waters of the Atlantic.

“In Nares Strait, the ice island will encounter real islands that are all much smaller in size,” he said.

“The newly born ice island may become land-fast, block the channel, or it may break into smaller pieces as it is propelled south by the prevailing ocean currents. From there, it will likely follow along the coasts of Baffin Island and Labrador, to reach the Atlantic within the next two years.”

Environmentalists say ice melt is being caused by global warming with Arctic temperatures in the 1990s reaching their warmest level of any decade in at least 2,000 years, according to a study published in 2009.

Current trends could see the Arctic Ocean become ice free in summer months within decades, researchers predict.

Source CNN

Events such as this one are not unusual, but rarely do scientists see them unfold in near real-time. Researchers working with the space agency spotted the rapid ice loss using high-resolution satellite imagery. Two such images tell the story. In the first image (above), a rift, which looks like a narrow horizontal line indicated by the red arrow, can be seen developing in the glacier. In the next image, taken a day later, the ice below the rift has collapsed into the sea and the location of the calving front has retreated.

Why does this glacier matter to me, you ask?

The short answer: sea level, although this particular event won’t raise the level of the Potomac or any other U.S. river anytime soon. Unlike the loss of sea ice, glacial melting causes sea level to increase, and the fate of glaciers like this one will play a key role in determining by how much sea level increases.

The Jakobshavn Isbrae is what is known as an outlet glacier, which the National Snow and Ice Data Center defines as “a valley glacier which drains an inland ice sheet or ice cap and flows through a gap in peripheral mountains.” In other words, it serves as a drainage pipe from the land ice into the ocean. According to NASA, the Jakobshavn Isbrae, which is located in western Greenland at about 69 degrees north latitude, is the largest outlet glacier in Greenland, draining 6.5 percent of Greenland’s ice sheet area.

Scientists at NASA, NOAA and other agencies are keeping close tabs on Greenland’s ice due to its significant ramifications for global sea level rise. If the entire Greenland ice sheet were to melt (a process that would likely take several centuries to play out, even with more global warming than we’ve already seen), sea level would rise by as much as an estimated 23 feet globally. NASA reports that “as much as 10 percent of all ice lost from Greenland is coming through Jakobshavn, which is also believed to be the single largest contributor to sea level rise in the northern hemisphere.”

Interestingly, this particular glacier has been retreating especially rapidly in recent years. As the below image shows, the ice front receded more 27 miles in 160 years, but in recent years the ice loss rate has increased, with six miles of retreat observed in just the past decade.

Recent studies have found that warming ocean temperatures may be responsible for much of the increased melting of Greenland’s outlet glaciers, and this may be accelerating the melting of the larger Greenland ice sheet. For example, one study published in Nature Geoscience in February concluded that glaciers in west Greenland are melting 100 times faster at their undersea end points than on the surface.

This event would support the ocean-driven melt theory, according to a NASA ice specialist.

“While there have been ice breakouts of this magnitude from Jakonbshavn and other glaciers in the past, this event is unusual because it occurs on the heels of a warm winter that saw no sea ice form in the surrounding bay,” said Thomas Wagner, cryospheric program scientist at NASA Headquarters, in a press release. “While the exact relationship between these events is being determined, it lends credence to the theory that warming of the oceans is responsible for the ice loss observed throughout Greenland and Antarctica.”

To get a measure of what’s truly going on, scientists look to the oceans — slow to heat up, slow to cool down, and thus less prone to short-term variations. Indeed, says John Lyman an oceanographer at the University of Hawaii, “about 80 or 90 percent of the extra heat absorbed by the planet is absorbed into the oceans.” That being the case, Lyman and several colleagues set about trying to see how the ocean’s heat content has changed over the past couple of decades. The result, appearing in the current issue of Nature, will give little comfort to climate change deniers: the oceans have been warming inexorably since at least 1993, at a rate broadly consistent with what you’d expect from the buildup of greenhouse gases. (See a photo gallery of climate change in Europe.)

There are some uncertainties in the numbers — not surprising, since the new study is essentially a synthesis of earlier papers, done by different groups using different instruments and making different sorts of measurements. “There’s a large amount of error in the data,” admits co-author Josh Willis, of NASA’s Jet Propulsion Laboratory, in Pasadena. “But the signal of global warming is abut six times larger than any uncertainties.” In particular, the so-called “global cooling” climate skeptics claim has been going on since 1998 doesn’t show up. “If you look at our data since 1998,” says Lyman, “it’s warmed significantly.” (The Gulf oil spill: Follow TIME’s latest news.)

The curve does flatten somewhat in 2003 — but that may have to do with things going on in the deep ocean. The sensors involved in the latest research go down only to about 2,300 ft., roughly half the average depth of the world’s oceans. The upper and lower ocean exchange heat just as the ocean and atmosphere do, and nobody really knows what’s happening near the bottom. Less than two months ago, in fact, Kevin Trenberth and John Fasullo, both climatologists at the National Center for Atmospheric Research, in Boulder, Colorado, published a paper in Nature suggesting that some of the extra heat trapped by greenhouse gases has gone missing — and that it might well be hiding in the deep oceans. Part of the problem, Trenberth suggested, was the same sort of incomplete measurements and inconsistencies in data processing Willis and Lyman describe in their own study. (See a special on December 2009′s COP15 Climate-Change Conference.)

Incomplete though the numbers are, however, the results seem reasonably robust — and they’re corroborated by another, entirely different set of measurements. As the oceans warm, they expand; indeed, up to half of sea-level rise comes not from melting glaciers or disappearing ice caps, but from the physical expansion of seawater as it heats up. And like the ocean’s heat content, the rise in sea level is gradual enough that over time, the year-to-year or even decade-long ups and downs disappear into a steady, long-term increase. “A century ago,” says Willis, “sea level was rising at about one millimeter per year. Fifty years ago it was two. And now it’s rising at three millimeters per year.”

In short, the oceans are currently doing the heavy lifting in absorbing trapped heat. Ultimately, though, some of that heat will be transferred back to the air, continuing to warm the places we live even if we manage to stop generating greenhouse gases at such a great rate. That makes it crucial to understand exactly what’s going on offshore. If scientists can refine their measurements, writes Trenberth in a commentary on this week’s Nature paper, “ocean heat content is likely to become a key indicator of climate change.” That key, in turn, may be one more tool to help slow the damage.

Lemonick is the senior science writer at Climate Central.

Source Time.com