Why icebergs melt

Energy drilling removed vast quantities of subsurface liquid, which studies suggest increased the rate at which the land is sinking. Now Louisiana is losing approximately 25 square miles 65 square kilometers of wetlands every year, and the state is lobbying for federal money to help replace the upstream sediments that are the delta's lifeblood. Local projects like that might not do much good in the very long run, though, depending on the course of change elsewhere on the planet.

Part of Antarctica's Larsen Ice Shelf broke apart in early Although floating ice does not change sea level when it melts any more than a glass of water will overflow when the ice cubes in it melt , scientists became concerned that the collapse could foreshadow the breakup of other ice shelves in Antarctica and allow increased glacial discharge into the sea from ice sheets on the continent.

If the West Antarctic ice sheet were to break up, which scientists consider very unlikely this century, it alone contains enough ice to raise sea level by nearly 20 feet 6 meters. Even without such a major event, the IPCC projected in its report that sea level will rise anywhere between 4 and 35 inches 10 and 89 centimeters by the end of the century.

The high end of that projection—nearly three feet a meter —would be "an unmitigated disaster," according to Douglas. Down on the bayou, all of those predictions make Windell Curole shudder.

Rising sea level is not the only change Earth's oceans are undergoing. The ten-year-long World Ocean Circulation Experiment , launched in , has helped researchers to better understand what is now called the ocean conveyor belt. Oceans, in effect, mimic some functions of the human circulatory system. Just as arteries carry oxygenated blood from the heart to the extremities, and veins return blood to be replenished with oxygen, oceans provide life-sustaining circulation to the planet.

Propelled mainly by prevailing winds and differences in water density, which changes with the temperature and salinity of the seawater, ocean currents are critical in cooling, warming, and watering the planet's terrestrial surfaces—and in transferring heat from the Equator to the Poles.

The engine running the conveyor belt is the density-driven thermohaline circulation "thermo" for heat and "haline" for salt. Warm, salty water flows from the tropical Atlantic north toward the Pole in surface currents like the Gulf Stream.

This saline water loses heat to the air as it is carried to the far reaches of the North Atlantic. The coldness and high salinity together make the water more dense, and it sinks deep into the ocean. Surface water moves in to replace it. The deep, cold water flows into the South Atlantic, Indian, and Pacific Oceans, eventually mixing again with warm water and rising back to the surface. Changes in water temperature and salinity, depending on how drastic they are, might have considerable effects on the ocean conveyor belt.

Ocean temperatures are rising in all ocean basins and at much deeper depths than previously thought, say scientists at the National Oceanic and Atmospheric Administration NOAA. Arguably, the largest oceanic change ever measured in the era of modern instruments is in the declining salinity of the subpolar seas bordering the North Atlantic.

Robert Gagosian, president and director of the Woods Hole Oceanographic Institution, believes that oceans hold the key to potential dramatic shifts in the Earth's climate. He warns that too much change in ocean temperature and salinity could disrupt the North Atlantic thermohaline circulation enough to slow down or possibly halt the conveyor belt—causing drastic climate changes in time spans as short as a decade.

The future breakdown of the thermohaline circulation remains a disturbing, if remote, possibility. But the link between changing atmospheric chemistry and the changing oceans is indisputable, says Nicholas Bates, a principal investigator for the Bermuda Atlantic Time-series Study station, which monitors the temperature, chemical composition, and salinity of deep-ocean water in the Sargasso Sea southeast of the Bermuda Triangle. Oceans are important sinks, or absorption centers, for carbon dioxide, and take up about a third of human-generated CO2.

Data from the Bermuda monitoring programs show that CO2 levels at the ocean surface are rising at about the same rate as atmospheric CO2. But it is in the deeper levels where Bates has observed even greater change.

In the waters between and 1, feet and meters deep, CO2 levels are rising at nearly twice the rate as in the surface waters. While scientists like Bates monitor changes in the oceans, others evaluate CO2 levels in the atmosphere.

In Vestmannaeyjar, Iceland, a lighthouse attendant opens a large silver suitcase that looks like something out of a James Bond movie, telescopes out an attached foot 4. Two two-and-a-half liter about 26 quarts flasks in the suitcase fill with ambient air. In North Africa, an Algerian monk at Assekrem does the same. Around the world, collectors like these are monitoring the cocoon of gases that compose our atmosphere and permit life as we know it to persist.

When the weekly collection is done, all the flasks are sent to Boulder, Colorado. There, Pieter Tans, a Dutch-born atmospheric scientist with NOAA's Climate Monitoring and Diagnostics Laboratory, oversees a slew of sensitive instruments that test the air in the flasks for its chemical composition. In this way Tans helps assess the state of the world's atmosphere. The Earth's glaciers have been silently retreating for more than half a century as climate change inexorably marches on.

There is no place on the planet — except south-east Asia — capable of withstanding the effects of a phenomenon that has melted more than 9.

These massive blocks of moving ice arise as snow accumulated in cold places compacts and recrystallizes, as is the case, for example, in mountain and polar glaciers, which should not be confused with the gigantic Arctic plates.

Glaciers are classified according to their morphology — ice fields, cirque glaciers, valley glaciers, etc. The formation of a glacier takes millennia, and its size varies depending on the amount of ice it retains throughout its lifespan. The behaviour of these masses is reminiscent of that of the rivers they feed during thaws, and their speed depends on friction and the slope of the terrain over which they move.

The rising temperature of the Earth has, without doubt, been responsible for melting glaciers throughout history. Today, the speed with which climate change is progressing might render them extinct in record time.

Let us take a detailed look at the causes behind glacial melting:. A glacier's life cycle. In the aforementioned study, the University of Zurich revealed that glacial melting has accelerated over the last three decades.

The main consequences of deglaciation are:. It elicits student ideas about density and buoyancy. It elicits student ideas about density. Modeling icebergs and learning about the glacier-iceberg connection can help students understand that icebergs are made from fresh water. Models can also be useful in illustrating the effects of land- and sea-based ice on sea-level rise.

When Floating Ice Melts in the Sea Grades Students use water and ice cubes to model what happens when floating ice melts. Students and teachers will observe that the melting of floating ice, such as icebergs and ice shelves, does not affect sea level. Challenge your students to modify the experiment to show what happens to land masses surrounded by water when ice melts. When Land Ice Melts Grades Students model the melting of land ice glaciers and ice sheets to discover that this type of melting does affect sea level.

Challenge students to think about the block of wood. Does this effectively model what would happen to the land? What does the water represent? How could they modify the procedure to investigate what happens to another body of land in the same ocean? It can be found all around the perimeter of Antarctica, typically at a depth of around 1, feet below the surface, according to University of Washington glacier expert Eric Steig. Multiple studies in the last few years have suggested that changes in wind patterns around Antarctica can alter the ocean currents driving the movement of this warm bottom water, sometimes causing more of it to well up around the ice sheet than is usual.

Winds do naturally fluctuate from one year to the next to a certain extent. But Chad Greene, a University of Texas, Austin, glacier expert who led the recent Totten study, notes that climate change is also thought to have an influence on Antarctic wind patterns.

Around Totten Glacier, he notes, some models suggest that the winds driving certain major ocean currents circulating around Antarctica will become more intense as the climate warms, pushing these currents farther south.

If this happens, these currents may help to drive cold surface water away from the pole and warm bottom water closer to the ice sheet. In fast-melting West Antarctica, he noted, wind patterns may be more strongly linked to changes in the tropics. This means that long-term climate-driven warming in the Pacific could also have a gradual effect on the conditions affecting glacier melt.

According to Eric Rignot, a glacier expert at the University of California, Irvine, a major factor in this process is that the tropics are warming at a faster rate than the South Pole. The opposite is true for the Arctic, which is warming faster than any other part of the planet.

This difference in warming rates causes a change in the temperature gradient between the equator and Antarctica, which alters the way air flows around the globe.

According to Steig, the Pacific is already experiencing some changes that may be driving recent increases in warm water upwelling around Antarctica.