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Calling it the most extensive review of how coral on Australia's Great Barrier Reef is faring, scientists on Monday reported some alarming news: The amount of coral covering reefs there has been cut in half since 1985 and will likely continue to decline unless steps are taken to at least attack the easiest of several factors.

"We show a major decline in coral cover from 28 percent to 13.8 percent" of the entire system, the experts wrote after reviewing 2,258 surveys of 214 reefs within the marine sanctuary. 

"Two-thirds of that decline has occurred since 1998," they added.

John Bruno, a coral expert who was not part of the study, called the findings "really grim" and reflecting loss even higher than deforestation in the tropics, a topic that generally gets much more attention.

"In 2007, we first sounded the alarm that the Great Barrier Reef, and Pacific reefs in general, were not as pristine and resilient as a lot of people wanted to believe," Bruno, a marine biology professor at the University of North Carolina Chapel Hill, told NBC News. "But still, this is really shocking to me."

"This is a really high rate of loss for an entire region," he added. "This is just nuts and it appears to have been sustained over the last five to 10 years. Just mind blowing. I really didn't expect this."

The researchers estimated that tropical storms, coral predation by crown-of-thorns starfish and coral bleaching accounted for 48 percent, 42 percent and 10 percent of the respective estimated loss in coral cover.

Coral bleaching, whereby coral expels the tiny single-celled algae inside that provide color, is triggered by stress such as warm seas or pollution.

The experts didn't have much faith in quick actions to counter warming seas, storms and bleaching, but they believe it might be possible to reduce starfish populations.

They based their hope on evidence that starfish are linked to poor water quality, and the fact that the northern Great Barrier Reef, which has little starfish predation, showed no overall decline. 

Nutrient-rich waters stimulate plankton, which starfish larvae thrive on, the experts noted, and if fertilizer and other nutrient-rich pollution in the water is cleaned up, starfish populations would decline and coral cover could increase by nearly a percentage point a year, they estimated. 

"Survival of the plankton-feeding larvae ... is high in nutrient-enriched flood waters, whereas few larvae complete their development in seawater with low phytoplankton concentrations," the experts wrote.

Bruno, for his part, said the impact of starfish on the reef is "striking," with the carnivores actually eating away at coral. "They are huge and scary beasts," he said, citing outbreaks in which the starfish "move in massive waves down the Great Barrier Reef like a plague."

Related: 360-degree tours of Great Barrier Reef

The study's authors predicted that without intervention the coral cover on the reef will probably decline up to 10 percent in the next 10 years.

They also noted that reducing starfish is a short-term step that can "only be successful if climatic conditions are stabilized, as losses due to bleaching and cyclones will otherwise increase."

The study by experts at the Australian Institute of Marine Science and the University of Wollongong was published in the peer-reviewed Proceedings of the National Academy of Sciences.

Bruno called the study "a sea change in the attitude" of the institute, a branch of the Australian government, because it had been "resistant to the idea that the Great Barrier Reef was degrading" — even challenging the 2007 study he and a colleague published.

"Ten years ago nearly everyone assumed, and argued, that due to its isolation, size and huge biodiversity, the Great Barrier Reef had resisted the decay that the rest of the world's reefs had experienced," Bruno added.

The study follows a report earlier this month estimating coral cover in the Caribbean and Florida Keys has fallen from 50 percent of reef surface area in the 1970s to just 8 percent today.  

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Chukot-TINRO

Tens of thousands of walruses make their home in Beringia, including these seen last fall at Cape Serdtse-Kamen in Chukotka, Russia.

You might have missed it, but the ancient land of Beringia has gotten some extra protection from superpowers Russia and the United States. 

That's right, Beringia -- 2,800 miles stretching from Siberia, across the Bering and Chukchi seas, through Alaska and into Canada's British Columbia. For thousands of years, Beringia even had a 1,000-mile-long land bridge that emerged when sea level dropped.

OK, so it's not an actual nation, but Beringia does have its own heritage of people divided by borders but united culturally -- and a natural kingdom of whales, polar bears, walruses and seals.

 "From the diversity of its Arctic wildlife, both on land and within its waters, to the bounty it provides that sustains cultures on both sides of the U.S.-Russian border, Beringia is home to a kingdom of wildlife and cultural riches, deserving of protection in perpetuity," Cristian Samper, president of the New York-based Wildlife Conservation Society, told NBC News.

"This announcement," he added, "brings us one step closer to that reality."

Samper was talking about a meeting between Secretary of State Hillary Clinton and her Russian peer earlier this month, where both nations agreed to work toward "a transboundary area of shared Beringian heritage" by 2013. 

National Park Service

That designation would create closer ties between two U.S. national parks -- the Bering Land Bridge Natural Preserve and the Cape Krusenstern National Monument -- with Russia's soon-to-be-designated Beringia National Park.

"Park managers and researchers from both countries will be able to increase their efforts to conserve this unique ecosystem as well as the cultural traditions and languages of the indigenous people on both sides of the (Bering) strait," Clinton said at the meeting on Sept. 8.

Even before the announcement, the U.S. National Park Service has had a program since the 1990s to promote Beringia, a term first coined in 1937.

Bob Gerhard / National Park Service

Anadyr, the capital of Russia's Chukotka Autonomous Region, is part of Beringia and faces the Bering Sea.

"As one of the world's great ancient crossroads, Beringia may hold solutions to puzzles about who were the first people to populate North America, how and when they traveled, and how they survived under such harsh climatic conditions," a website dedicated to Beringia reads.

The park service program stems from a 1990 announcement by then President George H. W. Bush and Soviet President Mikhael Gorbachev to establish an international park spanning the Bering Strait. 

A full-fledged international park never came about, in part because of suspicions by native groups. But the new, smaller approach is aimed at easing those concerns.

Vic Knox / National Park Service

Native festivals like this one are typical in Anadyr, a city in Russia's autonomous region of Chukotka that is part of the wider region known as Beringia.

The Wildlife Conservation Society is among the environmental groups excited about stronger cross-border ties. It already has a "Beringia Program" that looks at:

• How shipping in formerly ice-covered seas will affect marine life and indigenous people who rely on that for food.
• The threat walruses face from shrinking sea ice, which they rely on to rest while at sea. Less sea ice has led to overcrowding and even walruses crushed to death as they "haul out" by the thousands to rest on beaches.
• The impacts of human development on birds from around the world that nest and breed in the Arctic tundra.

Chukot-TINRO

Scientists are seeing more of these massive "haul outs" by walruses. These were seen last fall on Russia's Cape Serdtse-Kamen, part of the larger Beringia region.

The organization's "Beringia Program" manager sees the U.S.-Russia effort as keeping recent momentum moving forward. Both native peoples and wildlife, Martin Robards told NBC News, face living "in a region warming at twice the global average, while at the same time, adjusting to a rapid influx of new development interests."

As for the variety of wildlife, "it's phenomenal," Robards said. "In the fall and spring animals come through the Bering Strait -- whales, polar bears, walruses and seals."

That wealth makes it easy for Robards to spend his time on Beringia. But getting its importance across to others can be problematic, so having two superpowers raise Beringia's profile is a big plus.

"It does need explaining at times," he admits.

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New sea ice is finally starting to form again in the Arctic, scientists reported Wednesday, but not before reaching another record low last Sunday. 

"We are now in uncharted territory," Mark Serreze, director of the National Snow and Ice Data Center, said in a statement announcing the record low of 1.32 million square miles -- nearly half the average extent from 1979 to 2010. The extent has been tracked by satellite since 1979.

"While we’ve long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic," he added, "few of us were prepared for how rapidly the changes would actually occur."

Many experts expect the Arctic to be free of sea ice in summer at some point between 2015 and 2050.

"Recent climate models suggest that ice-free conditions may happen before 2050," noted center scientist Julienne Stroeve. But she added the caveat that the recent sudden rate of decline "remains faster than many of the models are able to capture."

Serreze told NBC News he's figuring on 2030, calling it "a pretty aggressive estimate."

The sea ice extent numbers come after the center reported last month that the summer sea ice on Aug. 26 had broken the previous record low set in 2007 of 1.61 million square miles. On Aug. 26 the sea ice extent was 1.58 million square miles, it said.

"We're smashing a record that smashed a record," center scientist Walt Meier said.

In the 1980s, he said, summer sea ice would cover an area a bit smaller than the Lower 48 states. Now it is about half that.

The difference between this year's low and that of 2007 is 293,000 square miles, about the size of Texas, the center noted in its report.

Meanwhile, conditions favorable to new sea ice are taking longer to appear.

"The strong late season decline is indicative of how thin the ice cover is," Meier said. "Ice has to be quite thin to continue melting away as the sun goes down and fall approaches."

The thickness of the ice is also in decline.

"The core of the ice cap is the perennial ice, which normally survived the summer because it was so thick", Joey Comiso, a NASA scientist who uses satellites to study the ice, said in a statement. "But because it's been thinning year after year, it has now become vulnerable to melt."

Related: China eyes mineral treasure in warming Arctic
Related: Starving female polar bear challenges male in warming sign

NASA also noted that a strong August storm that formed off Alaska's coast and moved to the center of the Arctic Ocean had an impact on ice levels.

"The storm definitely seems to have played a role in this year's unusually large retreat of the ice", said NASA scientist Claire Parkinson. "But that exact same storm, had it occurred decades ago when the ice was thicker and more extensive, likely wouldn't have had as prominent an impact, because the ice wasn't as vulnerable then as it is now."

This year follows several of declining summer sea ice.

"The six lowest September ice extents have all been in the past six years," Serreze said. "I think that's quite remarkable." 

The experts also noted that what happens in the Arctic doesn't stay there.

The warmer Arctic is adding increased heat and moisture into the climate system, said center scientist Ted Scambos. "This will gradually affect climate in the areas where we live," he said. "We have a less polar pole -- and so there will be more variations and extremes."

The Associated Press contributed to this report.

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Wildlife biologist Ian Bullock is a seasoned visitor to the Arctic, but even he was surprised by what he saw last month: a thin female polar bear, shadowed by her cub, trying to challenge a much bigger, stronger male for food.

It wasn't much of a challenge, but it showed just how desperate she was, Bullock told NBC News on returning from his 10th straight summer cruise to the Arctic.

That desperation, he feels, stems from the fact that the Arctic's summer sea ice — which polar bears using as floating stations from which to hunt seals — has been shrinking over the last few decades due to a warming Arctic, forcing polar bears into smaller areas and more intense competition. 

"She was the thinnest female with cub I have ever seen," he said. "She had a single cub which implies she has already lost one other cub this year.

"If she cannot feed, she cannot suckle her cub; with a hungry cub it is even harder for her to hunt effectively, so from what I saw her last cub is at risk and ultimately so is she," he added. "This is why she was challenging a big male with food. She was hungry enough to take a big risk." 

In a video filmed during the National Geographic Explorer cruise to the Arctic's Svalbard region, Bullock said it looks like that reduced ice is "really putting the bears under stress."

"The worst thing is when we've encountered bears, we've found them really packed in tight, in the last little areas of fast ice attached to land, or the last little patches of pack ice at sea," said Bullock, who served as a guide on the cruise ship. "And there they've been in competition."

Polar bears are listed as "vulnerable" and in decline by the International Union for Conservation of Nature, which estimates the population at no more than 25,000 across the Arctic.

The U.S., which has two Arctic regions where polar bears live, in 2008 listed its population as "threatened".

Last year, researchers cited three incidents where polar bears might even have resorted to cannibalism due to warming and reduced sea ice.

The diminished sea ice also got the attention of the National Geographic Explorer's skipper.

Captain Leif Skog told NBC News that he had e-mailed his boss, Sven Lindblad of Lindblad Expeditions, to describe "a shocking escalation of the reduction of sea ice."

One data graph he monitored daily, showing the total volume of Arctic sea ice, "could be called the death spiral of the Arctic sea ice," he said in his e-mail to Lindblad.

Because of the reduced sea ice, he added, the cruise was able to visit northeast Greenland "a month earlier than what was normal in the past."

"We expected to face some sea ice but everything was gone in the fjords upon our arrival," he added. "The sea water temperature in the fjords was also unbelievably high."

Another expert on the cruise called the outside temperature "surprisingly warm." 

"It was T-shirt weather," Paul Berkman, an environmental science professor at the University of California Santa Barbara, told NBC News. Berkman noted two other major Arctic developments over the summer:

• The amount of summer sea ice reached its lowest point in 30 years of records.
• Nearly the entire surface of Greenland's ice cap saw some melting in July, a phenomenon not seen in 150 years of ice records.

Berkman said the polar regions, and the Arctic in particular, show an "amplified response" to a warming climate ahead of other parts of the globe.

That response is twofold, he adds: Arctic temperatures have warmed 3-6 degrees F above the global average, and reduced ice removes huge amounts of reflective white from the sea and reveals a dark sea that absorbs heat.

The sea ice is like "a giant mirror on Earth's surface" he said. "Without summer Arctic sea ice, more heat from the sun is absorbed into the Earth system, which is a feedback that further accelerates warming of our climate."

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Reefs in the Caribbean and Florida Keys have lost most of the colorful corals that feed a rich ecosystem and made the region a diving and snorkeling mecca, a major conservation group reported Friday. On average, reefs have live coral on just 8 percent of their surface area, down from more than 50 percent in the 1970s.

Impacts including warming seas and human sewage have contributed to a steady decline that shows "no signs of slowing," the International Union for Conservation of Nature (IUCN) said in releasing its report, which was based on new data compiled by 36 experts earlier this year.

The decline was not uniform, the IUCN noted, and those areas with less human impact fared better. "Corals declined precipitously on the Jamaican north coast in the 1980s ... but not at Curacao and Bonaire where coral has more gently declined to about 25-30% today," the IUCN said in the report.

In contrast, total coral cover in the Florida Keys, the U.S. Virgin Islands and Puerto Rico "has progressively declined from 25 to 35% in the 1970s to less than 15% today."

Many of those severely deteriorated reefs instead are covered with large algae, which make it harder for coral to get established, "and virtually no fish larger than" a few inches, the report stated.

The report cited a number of factors causing the decline: disease, pollution, overfishing, hurricanes and "coral bleaching" — a process triggered by stress such as warm seas or pollution whereby the coral expels the tiny single-celled algae inside it that provide its color.

The IUCN did not try to weigh the importance of each factor, but some experts voiced their belief that global warming is paramount.

John Bruno, a University of North Carolina marine biologist who contributed to the new data, told NBC News that a study published last July shows the key driver in the decline is a warming ocean.

"Our preliminary analysis suggests that the state of Caribbean reefs continues to worsen, primarily due to ocean warming," he said. "To reverse this dire trend, job one is to halt the increase of greenhouse gas emissions."

Related: Study ties coral crisis to climate change
Related: Slideshow on threats to coral

The IUCN released the report at its annual convention and urged nations to step up efforts to reduce fossil fuel reliance, thereby reducing greenhouse gases. It also called on nations with coral reefs in their waters to take several actions:

• Limit fishing through catch quotas;
• Create or extend marine protected areas, which provide havens for coral and fish populations to recover;
• Halt runoff from land of sewage and fertilizers, among other pollutants.

The impacts on coral must be "immediately and drastically" reduced, said Carl Gustaf Lundin, director of IUCN’s Global Marine and Polar Program, "if coral reefs and the vitally important fisheries that depend on them are to survive in the decades to come."

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The amount of summer sea ice in the Arctic has reached a record low in three decades of satellite data, scientists reported Tuesday, with one of them describing recent warm years there as creating a "less polar pole." The decline was expected to continue for at least several more days before cold weather sets in and creates new ice through fall and winter.

The area of Arctic waters covered by sea ice was measured at 1.58 million square miles on Sunday, the National Snow and Ice Data Center (NSIDC) reported. That's below the previous record low of 1.61 million square miles set on Sept. 18, 2007, and in line with earlier expectations for the season.

"Including this year, the six lowest extents in the satellite record have occurred in the last six years," the center noted on its website.

"Parts of the Arctic have become like a giant Slushee this time of year" due to thinning ice, Walt Meier, a scientist at the center, told reporters.

That thinner ice also explains how a storm in early August made a significant impact in speeding up the decline this month, Meier said.

At NASA, which helps with the satellite data, scientist Claire Parkinson said the trend has been "strongly downward."

This visualization shows the extent of Arctic sea ice on Aug. 26, 2012, the smallest area in three decades of satellite records. The yellow line shows the average minimum summer ice coverage from 1979 to 2010.

The 2007 decrease "stunned" researchers since it was so large compared to previous years, she said, and "this year it's plummeting" further.

It's not just sea ice in summer that's been weakened, she added. "No matter what month you're in, it's less ice than it used to be decades ago," she said.

The researchers added that manmade emissions tied to global warming offer the best explanation for the decline.

Ted Scambos, a senior NSIDC researcher, told NBC News that no one weather pattern explains the downward trend. "Greenhouse gasses are the only consistent explanation for a persistently warming Arctic," he added.

"The Arctic was our refrigerator," he said, but the warmer weather of the last five or six years have meant "a less polar pole."

Scambos said the Arctic system is too variable to guarantee that each future year would show a decline, but over time he expects the decline to continue. "I think we can expect further declines to new records," he said, "and eventually, an ice-free North Pole."

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Just a week after scientists reported with alarm that 97 percent of Greenland had seen ice melting on the surface in mid-July, new data shows that after a brief refreeze much of the massive ice sheet has again seen melt.

Temperatures again warmed above freezing at key points between July 24-31, according to data provided to NBC News by Konrad Steffen, director of the Swiss Federal Institute for Forest, Snow and Landscape Research.

Thomas Mote, a climatologist at the University of Georgia at Athens, added that satellite imagery showed that the week peaked on Saturday with 74 percent of the giant ice sheet seeing melt. 

Typically, about a quarter of the ice sheet has melt on any given day in July, he noted.

"This event was almost as impressive as earlier this month, but didn't have quite as much melt in the north and northwest," Mote told NBC News.

"The big issue is simply the total amount of melt going on this summer, as opposed to any one day," he said. "Overall, we've had much earlier-than-normal and more extensive melting on Greenland this summer."

Like the mid-July melt, this one coincided with an "impressive ridge" of warm air sitting over Greenland, Mote noted.

Related story: 97 percent of Greenland sees ice melt

Mote said he's anxious to see satellite data at the end of summer showing any change to Greenland's total ice mass. "I would expect a very large loss of mass from the ice sheet this summer," he said.

Greenland ice cores do reveal that such thaws have happened every 150 years or so, but the fear now is that it might occur much more frequently due to warming sea and air temperatures. 

"If we continue to observe melting events like this in upcoming years, it will be worrisome," NASA glaciologist Lora Koenig said last week when the first data were released.

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Rob Bingham

The edge of the Ferrigno Ice Stream is seen from a plane. A valley below the stream as well as an offshore channel appear to be allowing relatively warmer sea water to eat away at the ice from below.

A newly discovered Antarctica valley buried by ice and as deep as the Grand Canyon could be contributing to rising sea levels, scientists reported Thursday.

The ancient topography is such that relatively warm sea water could be eating away at the ice edge -- and a question for future research is whether that process is happening elsewhere along Antarctica's coastal rift valleys. 

A few other ice-covered valleys have been found but the geology of this one, discoverer Rob Bingham told NBC News, shows that "the areas that are most vulnerable (to ice loss) coincide with areas of ancient rifting."

It seems the geological process over millions of years "preconfigures the topography to a shape that encourages ice loss," said Bingham, a glaciologist at Scotland's University of Aberdeen.

Reported in the peer-reviewed journal Nature, the find came about when Bingham was part of a British Antarctic Survey team looking at the Ferrigno Ice Stream, an area on the vulnerable West Antarctic Ice Sheet, to see why it was losing ice.

"It was in doing this that we discovered the ice in this region is underlain by a rift" a mile deep in places, Bingham said. Radar showed that "ice losses are concentrated over the rift," he added, allowing researchers to conclude that "the rift topography exacerbates the current ice losses."

Ice from the rift also carved a channel over millions of years that is now covered by coastal seas and appears to be allowing relatively warmer water to "flow back towards the Antarctic ice margin" and then melt it, Bingham said.

The melt causes the ice surface slope to steepen "and this in turn accelerates ice flow such that the ice surface drops over time. The presence of the rift valley facilitates this flow and is thus contributing to gradual depletion of the central ice cover."

Others scientists said the discovery would help better understand the dynamics of Antarctica.

Rob Bingham

This illustration shows the Ferrigno Ice Stream, outlined in black and just above a channel, seen in green, that appears to allow relatively warmer water to eat away at the ice margin.

"There could be more rifts like this and the study gives us ideas to test in other places," Tom Wagner, who manages NASA's ice research programs, told NBC News. Such rifts, he added, "could potentially cause very rapid ice flow."

Related story: Sudden vast ice melt seen on Greenland

The British Antarctic Survey agreed on the significance.

"The West Antarctic Ice Sheet is of great scientific interest and societal importance as it is losing ice faster than any other part of Antarctica with some glaciers shrinking by more than one meter (three feet) per year," it said in a statement coinciding with the study.

"Thinning ice in West Antarctica is currently contributing nearly 10 percent of global sea level rise," added BAS scientist David Vaughan. "It's important to understand this hot spot of change so we can make more accurate predictions for future sea level rise."

Study co-author Fausto Ferraccioli, a BAS scientist, told NBC News that satellite and aircraft surveys over the rift would help better explain the dynamics.

"We now need new airborne geophysical surveys both onshore and offshore," he said, in order to understand all facets of "this changing part of the West Antarctic Ice Sheet."

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Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

About 40 percent of Greenland's ice sheet thawed at or near the surface on July 8. Four days later, the melt had dramatically accelerated and an estimated 97 percent of the ice sheet surface had thawed.

Three satellites found that 97 percent of Greenland -- the land mass second only to Antarctica for its volume of ice -- underwent a thaw never before seen in 33 years of satellite tracking, NASA reported Tuesday.

Satellite experts at first didn't trust their readings, especially since they showed an incredible acceleration. Over four days, Greenland's ice sheet -- which covers 683,000 square miles -- went from 40 percent in thaw to nearly entirely in thaw.

"This was so extraordinary that at first I questioned the result: Was this real or was it due to a data error?" Son Nghiem of NASA's Jet Propulsion Lab in Pasadena, Calif., said in NASA's statement about the findings.

Scientists on the ground in Greenland had been reporting an unusually warm summer thaw, including damage at a snow airfield and strong runoff threatening a bridge, Tom Wagner, who manages NASA's ice research programs, told NBC News.

Ice cores from Greenland's highest region do reveal that such island-wide thaws have happened every 150 years or so, at least over the last few thousand years, but the fear now is that it might occur much more frequently due to warming sea and air temperatures.

"We can't lose sight of the fact that Greenland's ice sheet is losing 150 gigatons of ice a year," Wagner said. That translates into raising sea levels by one-one hundredth of an inch. Additionally, the danger of greater warming and greater melt persists. 

"If we continue to observe melting events like this in upcoming years, it will be worrisome," said Lora Koenig, a NASA glaciologist who helped analyze the satellite data.

Monitoring stations on land "showed temperatures above freezing, confirming that the surface was melting for the entire ice sheet," Konrad Steffen, director of the Swiss Federal Institute for Forest, Snow and Landscape Research, told NBC News.

Since then, he added, "temperatures have fallen below freezing for the higher elevations but still are melting below 1500 meters."

The director of the top ice research center in the U.S. said the discovery fits into "the larger picture of a strongly warming Arctic."

"Arctic sea ice extent this summer is so far tracking at very low, near record levels, and the ice cover is unusually diffuse," Mark Serreze of the National Snow and Ice Data Center told NBC News.

On top of that, he said, the seasonal melt that followed the 2012 winter "started unusually early over most of the Arctic Ocean."

The center's latest report, issued Tuesday, noted that" Arctic sea ice continued to track at levels far below average through the middle of July, with open water in the Kara and Barents seas reaching as far north as typically seen during September."

Thomas Mote, a University of Georgia climatologist who looked at the satellite data, said the melt followed an unusual series of warm air ridges over Greenland since late May, with the strongest coinciding with the rapid thaw in mid-July.

Each successive ridge, Mote told NBC News, was "stronger than the previous one" and it looks like the pattern has finally broken down. 

The ridges happened just as a cyclical weather phase known as the North Atlantic Oscillation shifted. "Together, they produced near perfect conditions for this event," Mote added.

Related: Huge Greenland iceberg breaks off glacier

Because they hold so much ice on land, Greenland and Antarctica have the potential to raise sea levels significantly if warming continues or worsens. 

Sea levels have already risen by about 8 inches in the last century, partly due to some ice melt but also thermal expansion caused by warming seas.

The U.N. climate panel estimates sea level could rise between 7 inches and nearly two feet this century -- the latter a scenario that could prove catastrophic for many coastal areas around the globe.

NASA said researchers had not yet determined whether this summer's Greenland thaw would be significant enough to raise sea levels.

Greenland has enough ice to raise sea levels by 23 feet if it all melted off.

A recent study found that it could take a long-term increase in global temperatures of just 2-3 degrees Fahrenheit to completely melt Greenland's ice sheet in 2,000 years. 

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Richard B. Aronson

Ian Macintyre, left, of the Smithsonian Institution and Steven Vollmer of Northeastern University pull out a core sample for the coral study they were co-authors on.

Coral reefs along Panama's Pacific coast completely collapsed for 2,500 years due to natural climate cycles, researchers reported in a study Thursday, adding that there's a lesson in the data for man-made climate change: ease up on greenhouse gasses and reefs will restore themselves.

"We can prevent coral reefs from shutting down again or recover them if they do shut down by reducing concentrations of greenhouse gases in the atmosphere and the ocean," study co-author Richard Aronson, a biology professor at Florida Institute of Technology, told msnbc.com.

The researchers reconstructed 6,000 years of coral reef history by driving pipes into reefs to pull out core samples. 

"We were shocked to find that 2,500 years of reef growth were missing," Lauren Toth, the lead author and a doctoral student, said in a statement announcing the study in the journal Science. 

The team found the same gap in earlier studies by other researchers as far away as Australia and Japan, and tied the collapse to an intensification of the natural climate cycle that produces El Nino and La Nina weather events.

Aronson emphasized that the fact that coral reefs returned does not mean mankind can expect them to survive a climate made warmer by industrial emissions of carbon dioxide.

"It is quite the opposite," he said. "Environmental pressure caused the reef ecosystems to collapse, and relieving that pressure allowed recovery."

"The same message," he added, "applies to human-caused climate change: by changing the climate we are stressing corals and coral-reef ecosystems, and we will have to stop doing that if we are going to save the reefs."

John Bruno, a marine biology professor at the University of North Carolina at Chapel Hill, said the study is valuable for showing that the biggest threat facing coral reefs is climate change.

Lauren T. Toth

This coral on Panama's Pacific coast was bleached by a 2010 warming event triggered by El Nino.

"Our modern coral reefs are supremely sensitive to subtle changes in climate even in the absence of local impacts like fishing and pollution," he wrote in a commentary for msnbc.com.

"In other words, in contrast to what has been argued in a number of high profile essays, reefs do not have to be overfished and polluted to be harmed by climatic fluctuations," wrote Bruno, who was not involved in the study.

"Everyone agrees that overfishing, particularly the depletion of predators from coral reef ecosystems, is an enormous, global problem," he added. "But the current science indicates that this problem is largely unrelated to the climate change problem. We urgently need to tackle both problems -- simultaneously and with equal vigor and commitment. Unfortunately, solving one will not negate the other."

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Kathryn Hansen / NASA

Arctic melt ponds visited during a July 2011 expedition on the U.S. Coast Guard Cutter Healy gave scientists a chance to find "windows from the sky to the ocean" that are perfect for phytoplankton blooms.

Experts were shocked to find a thick, 60-mile-long "phytoplankton megabloom" under Arctic sea ice, announcing in a study Thursday that ice made thinner by warming temperatures has, for now at least, created ideal conditions for the microscopic, single-cell plants to flourish.

More blooms are likely hidden under the ice, making for "ecological shifts" in Arctic waters that favor some species over others since phytoplankton are the base of the marine food chain, Stanford professor and lead researcher Kevin Arrigo told msnbc.com.

Scientists had thought Arctic phytoplankton blooms only happened after sea ice melted in summer, so the discovery is "like finding the Amazon rainforest in the middle of the Mojave Desert," added Paula Bontempi, who manages the ocean biology program at NASA, which funded the research.

"The waters literally looked like pea soup," Arrigo said at a press conference announcing the study in the journal Science. "It was as thick as a 5-year-old child is tall."

The team discovered the bloom in July 2011 in thin sea ice pocketed with ponds of melted ice on the Chukchi Sea off northern Alaska. Arctic sea ice has been shrinking and thinning in summer since 1979, the result of warming temperatures over the region. 

Those melt ponds proved crucial, allowing just enough light to get the growth process started while also protecting the algae from ultraviolet radiation.

"They were the windows from the sky to the ocean," said researcher Don Perovic, an ice scientist with the U.S. Army Corps of Engineers.

"If I were a phytoplankton," Perovic added, "that's where I'd want to live."

Arrigo said in his 25 years of studying phytoplankton blooms he had never seen one this large. Blooms in open water are much smaller, he noted, while very thick ice won't allow any light in to start photosynthesis.

"It's going to be a more productive system," Arrigo said, noting that plankton bottom feeders will benefit as the plankton sinks to the bottom of the Chukchi, much of which is around 160 feet deep.

The researchers didn't expect Arctic sea ice to disappear completely, since winters are still very cold, but they did note some potential downsides.

Some fish species that rely on mid-level nutrients will suffer, Arrigo said, and the bigger issue is that a warming Arctic appears to be triggering phytoplankton blooms earlier.

Species that can't adapt "to be there at the right time of year" will suffer, Arrigo said.

NASA funded the expedition as a way to match the satellite-based data it gathers on the Arctic with data gathered on the ice.

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Ralph Timmermann / Alfred Wegener Institute

Part of Antarctica's Filchner-Ronne Ice Shelf is seen in the Weddell Sea. Two new studies project the shelf will disappear by 2100, potentially releasing ice trapped on Antarctica's largest ice sheet.

Scientists have long focused on Antarctica’s smaller ice sheet as being vulnerable to warming, but two new studies project that part of the continent's much larger ice sheet is also at risk -- and that ice now held back on land there could add to sea level rise by 2100.

"This is the first legitimate evidence that this part of Antarctica is in play," Bob Bindschadler, a NASA earth scientist who has studied Antarctica for 30 years, told msnbc.com. "The potential, the reservoir of ice ... is vast."

In fact, that area, known as the East Antarctic Ice Sheet, has 10 times as much ice as the West Antarctic Ice Sheet. 

One study, published Wednesday in the journal Nature, used a computer model to project what would happen in Antarctica's Weddell Sea if temperatures rose in line with U.N. projections for 2100. 

The result was a change in ocean circulation and a temperature increase that would disintegrate the now-intact Ronne-Filchner Ice Shelf, with warmer water eating away from underneath.

Ice shelves like Ronne-Filchner sit on water, and thus their disintegration can't raise sea levels directly. But they also hold back ice sheets that sit atop land -- and those would start to drain into the sea if shelves weren't there to block them.

The Ronne-Filchner shelf is unusual in that it "sits on the fence" between Antarctica's two ice sheets, so it "can affect both sides," said Bindschadler, who was not involved in the research.

The finding echoes earlier research showing a similar warming effect in the Amundsen Sea on the other side of the Antarctic Peninsula. Ice shelves along the Amundsen Sea coast have weakened in recent decades. 

"The Weddell Sea is as vulnerable as the Amundsen Sea," study co-author Hartmut Hellmer of Germany's Alfred Wegener Institute said at a press conference, "and it affects a much larger ice shelf."

"We found a mechanism which drives warm water towards the coast with an enormous impact on the Filchner-Ronne Ice Shelf in the coming decades," he added in a statement released with the study.

National Snow and Ice Data Center

The Ronne-Filchner ice shelf, seen in blue, sits between Antarctica's two ice sheets, which are divided by the Transantarctic Mountains going from that ice shelf to the Ross ice shelf.

"It appears all hell could break loose there, too," added Bindschadler.

The second study, published in Nature Geoscience on Wednesday, found that near the Ronne-Filchner ice shelf the West Antarctic Ice Sheet has a slope that would accelerate melt since warmer seas would flow toward the ice being held back on land.

That scenario, said Bindschadler, "sets off alarms in my mind."

The study authors -- and Bindschadler -- emphasized that the east sheet has not started eroding but they certainly worry about the potential.

Alfred Wegener Institute

The scenario seen by researchers includes warming seas that reduce sea ice and eat away at the bottom of the Ronne-Filchner ice shelf.

"It still doesn't look like they've done much," Bindschadler said of the ice streams that could flow into the Weddell Sea, "but lo and behold, the vulnerability is perhaps greater than the ice shelves we've been focused on recently."

Tom Wagner, also a NASA earth scientist who studies ice, said the work was "the first to tie everything together -- from the ocean through to the glaciers.

"While all projections have uncertainty," he added, "the physical processes considered here are well known and the extrapolations reasonable." 

Just how much ice could escape into the sea -- and raise global sea levels -- if the Ronne-Filchner ice shelf disintegrated is the big unknown. 

The two studies didn't look at that aspect but "we think there is cause for concern," said Martin Siegert, co-author of the slope study and a University of Edinburgh researcher.

Another group at the Alfred Wegener Institute is now studying the potential impact on sea levels. 

If the ice sheet flow toward the sea is as great as the ice shelf loss, the institute said in its statement, then global sea levels would rise 0.17 inches a year.

That might not sound like much, but sea levels rose by just 0.05 inches a year from 2003 to 2010 due to ice melt, the institute noted. 

Moreover, the U.N. Intergovernmental Panel on Climate Change projects other sources will raise sea levels between seven inches and two feet by 2100, potentially flooding many low-lying areas.

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