Antarctic Iceberg Flotilla Caused Huge Sea-Level Rise
Frank Roedel, Alfred Wegener Institute
New evidence links rapid sea level rise 14,500 years ago to icebergs breaking off Antarctica.
John Hyde/Design Pics/Corbis
The effects of global warming are frequently projected decades into the future, but two recent reports -- one from theU.S. Global Change Research Program
and the otherfrom the U.N.
-- put into sharp focus visible consequences of our warming planet. An increase in temperature, extreme weather, loss of ice and rising sea level are just a few of changes we can measure right now. Let's take a look at some of the most concerning trends.BLOG: War Of The Words: Climate Change Or Global Warming?
Glaciers are shrinking worldwide and permafrost is thawing in high-latitude and high-elevation areas, reports this year's Fifth Assessment Report from the Intergovernmental Panel on Climate Change.BLOG: Dire Outlook For Climate Impacts, New Report Says
Only a few extinctions are attributed to climate change, reports the IPCC, but climate change that occurred much more slowly, over millions of years, caused major ecosystem shifts and species extinctions. Land and sea animals are changing their geographic ranges and migratory patterns due to climate change.NEWS: Climate Change: Why Haven't We Done More?
Sea level around the world has increased by about 8 inches since 1880, reports the 2014 National Climate Assessment, which projects a 1 to 4 foot rise by the end of the century.PHOTOS: Craziest Environmental Ideas (That Could Work)
Massimo Brega/The Lighthouse//Vi/Visuals Unlimited/Corbis
Excess CO2 is dissolving in the ocean and decreasing the pH of seawater. The ocean is about 30 percent more acidic than it was in pre-industrial times. More acidity in the oceans makes it harder for animals to form calcium carbonate shells and skeletons and erodes coral reefs.11 Health Threats from Climate Change
The probability of a Sandy-like storm deluging New York, New Jersey and other parts of the East Coast has nearly doubled compared to 1950, according to the American Meteorological Society. Even weaker storms will be more damaging now than they were 10 years ago because of rising sea levels. Superstorm Sandy cost the nation $65 billion, according to the 2014 National Climate Assessment, and 2012's Hurricane Isaac cost $2.3 billion.
The global sea level rises along with the temperature for two major reasons. For one, heat causes water to expand, which causes the existing water to take up more space and encroach on the coast. At the same time, ice at the poles and in glaciers melts and increases the amount of water in the oceans.PHOTOS: Melting Glaciers
Across the United States, heavy downpours are on the rise, especially in the Northeast and Midwest. Increases in extreme precipitation are expected for all U.S. regions, reports the 2014 National Climate Assessment.NEWS: Shrinking Greenland Glacier Smashes Speed Record
Ted Soqui/Ted Soqui Photography/Corbis
The most recent IPCC report states with "very high confidence" that current climate-related extremes like heat waves, droughts, floods, cyclones and wildfires are showing that countries around the world, at all development levels, are significantly unprepared. The American Meteorological Society estimates that approximately 35 percent of the extreme heat in the eastern United States between March and May 2012 resulted from human activities' effects on climate. The AMS warned that deadly heat waves will become four times more likely in the north-central and northeastern United States as the planet continues to warm.NASA: Global Warming Goes On
Antarctica's melting glaciers launched so many icebergs into the ocean 14,600 years ago that sea level rose 6.5 feet (2 meters) in just 100 years, a new study reports. The results are the first direct evidence for dramatic melting in Antarctica's past — the same as predictions for its future.
"The Antarctic Ice Sheet had been considered to be fairly stable and kind of boring in how it retreated," said study co-author Peter Clark, a climate scientist at Oregon State University. "This shows the ice sheet is much more dynamic and episodic, and contributes to rapid sea-level rise."
Natural climate warming caused huge ice sheet collapses in Antarctica eight times in the past 20,000 years, according to the study, published today (May 28) in the journal Nature. Measurements at Antarctica's biggest glaciers, such as Thwaites and Pine Island, suggest the ice sheet is on the brink of a similar massive retreat. [Photos: Antarctica's Pine Island Glacier Cracks]
Antarctica's glaciers have been shrinking since the last great ice age ended about 22,000 years ago. This warming was triggered by wobbles in Earth's orbit, combined with warming boosts from the ocean and atmosphere, such as temperature increases from the release of carbon dioxide gas.
The last big iceberg release was 9,000 years ago, and the pace of glacial retreat slowed in Antarctica until the 20th century, when melting picked up again with man-made climate change. Current models suggest global warming has again tipped the Antarctic Ice Sheet into sudden, rapid shrinking.
But models that forecast the future of Antarctica's Ice Sheet based on its past behavior actually had little hard evidence for making comparisons until now, Clark said.
New evidence links rapid sea level rise 14,500 years ago to icebergs breaking off Antarctica.Frank Roedel, Alfred Wegener Institute
Drilling for clues
To find out how the ice sheet fared under natural warming conditions, researchers drilled deep into the Scotia seafloor between Antarctica and South America. They discovered sandy debris from eight iceberg surges in the past 20,000 years. Icebergs carry sand trapped in ice out to sea, and the sediment falls onto the ocean floor as the frozen chunks melt.
The biggest pulse of debris was 14,600 years ago, at the same time as a global sea-level rise of about 13 feet (4 m) within 100 years, said study co-author Axel Timmermann, a climate scientist at the University of Hawaii at Manoa. Because ice sheets in the Northern Hemisphere were melting at the same time, scientists think Antarctica's melting accounts for about half of this jump in sea level, he said.
When glaciers draw back, they drop icebergs that melt and raise sea level. Ice melting from contact with warmer seawater can also contribute to sea-level rise.
During this period of rapid sea-level rise, dubbed meltwater pulse 1A, sea level rose 20 times faster than today's rate. Between 14,650 and 14,310 years, the oceans encroached on land by an astonishing 46 to 59 feet (14 to 18 m), or 13 feet (4 m) per century.
"The question has been, 'Where did this ice come from?'" Clark told Live Science. "This is the first clear evidence Antarctica did contribute to this sea-level rise."
The findings suggest that Antarctica's giant glaciers respond to a warming climate with pulses of quick withdrawal, rather than a slow and steady retreat. But the discovery does not answer one of Antarctica's biggest mysteries — what triggered the melting, and why did the glaciers stop their galloping retreat. Nor do researchers know which parts of the ice sheet were responsible for the icebergs, though they suspect it was primarily the Antarctic Peninsula and the Weddell Sea region.
Modeling suggests that the massive melting causes ocean circulation changes that prompt a feedback loop, letting warmer ocean water reach the ice, Timmermann said. "There is a positive feedback that can happen," he said.
More From LiveScience:
Photo Gallery: Antarctica's Pine Island Glacier Cracks
lar Ice-Melt Causes Sea-Level Rise, Satellites Find
In Images: IceBridge Investigates Antarctica