Ice Sheets

Thousands of years ago, the West Antarctic ice sheet shrank dramatically—then grew back in an unexpected way.

Volcanic eruptions have been known to cool global climate, but they can also accelerate melting of ice sheets by changing the surface reflectance of the ice.

Christine McCarthy, a geophysicist at the Lamont-Doherty Earth Observatory, scrunches blocks of ice between hunks of rock to study how ice behaves under pressure. Her work provides an important piece of the puzzle of how glaciers move, what makes them speed up, and how they are contributing to sea level rise as the climate warms.

Antarctica’s ice locks up enough fresh water to inundate coastal regions around the globe. And the ice is on the move: The continent’s vast glaciers are sliding toward the coast and out over the ocean, forming huge ice shelves that in some places are collapsing. Researchers from the Lamont-Doherty Earth Observatory have spent the last two Antarctic summers flying over the massive Ross Ice Shelf, deploying a custom-made package of instruments to probe the ice. Their goal: to untangle the interactions between ice, ocean and land, to try and gauge the effects of warming climate.

Scientists have found evidence in a chunk of bedrock drilled from nearly two miles below the summit of the Greenland Ice Sheet that the ice nearly disappeared for an extended time in the last million years or so. The finding casts doubt on assumptions that Greenland has been relatively stable during the recent geological past, and implies that global warming could tip it into decline more precipitously than previously thought. Such a decline could cause rapid sea-level rise. The findings appear this week in the leading journal Nature.

Figuring out how far sea level rose during past warm periods in Earth’s history starts with a walk on the beach, a keen eye for evidence of ancient shorelines, and a highly accurate GPS system. The math isn’t as simple as subtracting the distance from the old shoreline to the water’s edge, though. As massive ice sheets retreated during past ice ages, their weight on the land below lifted and the land rebounded. On longer time scales, circulation within the Earth’s mantle has changed the shape and height of the crust, as well.

Twenty-three million years ago, the Antarctic Ice Sheet began to shrink, going from an expanse larger than today’s to one about half its modern size. Computer models suggested a spike in carbon dioxide levels as the cause, but the evidence was elusive – until now. Ancient fossilized leaves retrieved from a lake bed in New Zealand now show for the first time that carbon dioxide levels increased dramatically over a relatively short period of time as the ice sheet began to deteriorate. The findings raise new questions about the stability of the Antarctic Ice Sheet today as atmospheric CO₂ concentrations rise to levels never before experienced by humans.

A 4,000-foot-high mountainside collapsed in Glacier Bay National Park in a massive landslide that spread debris for miles across the glacier below. It was a powerful reminder of the instability of the mountains in this part of Alaska and the risks that that instability creates. Scientists at Lamont discovered the landslide from its seismic signature and are studying it and another recent Alaska landslide and tsunami to improve understanding of landslide risks to this region and globally.

In southern Greenland in summer, rivers have been streaming off the ice sheet, pouring cold fresh water into the fjords. Attention has focused on the West Coast, where the majority of the meltwater has been entering the ocean in recent years, but a new study from Lamont's Marco Tedesco suggests that a greater risk to global climate may actually be coming from the East.

Humans have been burning fossil fuels for only about 150 years, yet that has started a cascade of profound changes that at their current pace will still be felt 10,000 years from now, a new study shows. Coastal areas, in particular, will experience the long-term effects as rising seas slowly redraw the world map as we know it and continue to rise long after emissions are brought down. Even in a scenario in which global temperatures warm to only about 2° Celsius above pre-industrial times, the analysis shows that several of the world’s coastal megacities will eventually be submerged.

Over the last century, glaciers in Greenland have been retreating quickly – at a rate at least twice as fast as any other time in the past 9,500 years, according to a new study. The study also provides new evidence for just how sensitive glaciers are to temperature changes, showing that they responded to abrupt and even short-lived cooling and warming in the past that lasted decades to centuries.

A snapshot of the changing climate of the West Antarctica Peninsula, where the impact of fast-rising temperatures provides clues about future ecosystem changes elsewhere.

A new study has found that powerful winds are removing massive amounts of snow from parts of Antarctica, potentially boosting estimates of how much the continent might contribute to sea level. Up to now, scientists had thought that most snow scoured from parts of the continent was simply redeposited elsewhere on the surface. However, the new study shows that in certain parts, called scour zones, some 90 percent—an estimated 80 billion tons per year—is instead being vaporized, and removed altogether. 

Summers on the Norwegian archipelago of Svalbard are now warmer than at any other time in the last 1,800 years, including during medieval times when parts of the northern hemisphere were as hot as, or hotter, than today, according to a new study in the journal Geology.

Stronger ocean currents beneath West Antarctica’s Pine Island Glacier Ice Shelf are eroding the ice from below, speeding the melting of the glacier as a whole, according to a new study in Nature Geoscience. A growing cavity beneath the ice shelf has allowed more warm water to melt the ice, the researchers say—a process that feeds back into the ongoing rise in global sea levels. The glacier is currently sliding into the sea at a clip of four kilometers (2.5 miles) a year, while its ice shelf is melting at about 80 cubic kilometers a year - 50 percent faster than it was in the early 1990s - the paper estimates.

Scientists still puzzle over how Earth emerged from its last ice age, an event that ushered in a warmer climate and the birth of human civilization. In the geological blink of an eye, ice sheets in the northern hemisphere began to collapse and warming spread quickly to the south. Most scientists say that the trigger...

North American Ice Sheet Dwindled Fast in Conditions Like Today's

In the face of warming climate, researchers have yet to agree on how much and how quickly melting of the Greenland ice sheet may contribute to sea level rise.

Lying beneath more than two miles of Antarctic ice, Lake Vostok may be the best-known and largest subglacial lake in the world, but it is not alone down there. Scientists have identified more than 145 other lakes trapped under the ice. Until now, however, none have approached Vostok’s size or depth.