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. Walking through the various labs filled with cylinders of standardized gas mixtures, absolute manometers, and gas chromatographs, Tans offers up a short history of atmospheric monitoring. In the late s a researcher named Charles Keeling began measuring CO2 in the atmosphere above Hawaii's 13,foot 4,meter Mauna Loa.
The first thing that caught Keeling's eye was how CO2 level rose and fell seasonally. That made sense since, during spring and summer, plants take in CO2 during photosynthesis and produce oxygen in the atmosphere. In the fall and winter, when plants decay, they release greater quantities of CO2 through respiration and decay.
Keeling's vacillating seasonal curve became famous as a visual representation of the Earth "breathing. Analysing images taken by NASA 's Terra satellite, they found that between , the world's glaciers lost an average of billion tonnes of ice each year. That's enough water to submerge Switzerland under six metres 20 feet of water -- every single year.
But the team also found that the rate of glacier melt had accelerated sharply during the same period. Between and , glaciers lost billion tonnes of ice per year. But between , they lost an average of billion tonnes each year. This glacial melt has contributed to 21 percent of sea level rises in the study period, the researchers said -- equivalent to 0. Immense computing power was brought to bear on the process of interpreting these pictures and pulling out the changes in the glaciers' elevation, volume and mass up to That's in large part because every single glacier examined in the study is represented based on the same methodology.
A group led from Leeds University published its own assessment of glacier ice loss in January in the journal The Cryosphere. It arrived at very similar numbers. Most of Earth's glaciers are melting faster than ever because of human-caused climate change, dumping about billion tons of melted ice into the world's oceans each year, according to a new study. In fact, what was once considered to be permanent ice has declined in volume almost everywhere around the globe, the study found. The estimates were based on high resolution 3D mapping of more than , glaciers, which is nearly all the glaciers on Earth.
The analysis is the most comprehensive and accurate of its kind to date.
0コメント