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http://sciencenow.sciencemag.org/cgi/content/full/2006/215/4
Over the past century, more and more fresh river water has been spilling off the continents into the oceans. But mysteriously, no change in overall precipitation can account for this increased flow. The net loss of water is worrying because it increases the risk of drought. Scientists have suspected that human-induced climate change is to blame, but it has proved difficult to finger just where the water budget has sprung a leak.
To crack the case, a team led by Nicola Gedney, a climatologist at the Hadley Centre for Climate Prediction and Research in Wallingford, U.K., and colleagues simulated the past century of weather on Earth. The researchers tweaked four climate change variables: increasing temperatures, changes in global vegetation, the dimming of the sun due to hazier skies, and higher concentrations of carbon dioxide in the atmosphere. They compared how river run-off is affected while introducing each factor separately, and then all four together.
Rising carbon dioxide levels alone appear to have caused the leak. A statistical analysis of the simulations revealed that increasing levels of the greenhouse gas are the main driver of river run-off, but not through global warming. Instead, CO2 is acting as a plant antiperspirant. Plants respond to increased levels of the gas by letting less water evaporate through their pores--known as stomata--and consequently taking up less water from the soil. This leaves extra water in the ground, which is eventually lost to river runoff rather than keeping the air moist--which would keep it circulating as fresh water.
The most severe low-oxygen ocean conditions ever observed on the West Coast of the United States have turned parts of the seafloor off Oregon into a carpet of dead Dungeness crabs and rotting sea worms, a new survey shows. Virtually all of the fish appear to have fled the area.
Scientists, who this week had been looking for signs of the end of this “dead zone,” have instead found even more extreme drops in oxygen along the seafloor. This is by far the worst such event since the phenomenon was first identified in 2002, according to researchers at Oregon State University. Levels of dissolved oxygen are approaching zero in some locations.
OSU scientists with the university-based Partnership for Interdisciplinary Studies of Coastal Oceans, in collaboration with the Oregon Department of Fish and Wildlife, used a remotely operated underwater vehicle this week to document the magnitude of the biological impacts and continue oxygen sampling. This recent low-oxygen event began about a month ago, and its effects are now obvious.
Any level of dissolved oxygen below 1.4 milliliters per liter is considered hypoxic for most marine life. In the latest findings from one area off Cape Perpetua on the central Oregon coast, surveys showed 0.5 milliliters per liter in 45 feet of water; 0.08 in 90 feet; and 0.14 at 150 feet depth. These are levels 10-30 times lower than normal. In one extreme measurement, the oxygen level was 0.05, or close to zero. Oxygen levels that low have never before been measured off the U.S. West Coast.
A correlation between a global average of low cloud cover and the flux of cosmic rays incident in the atmosphere has been observed during the last solar cycle. The ionising potential of Earth bound cosmic rays are modulated by the state of the heliosphere, while clouds play an important role in the Earth’s radiation budget through trapping outgoing- and reflecting incoming radiation. If a physical link between these two features can be established, it would provide a mechanism linking
solar activity and Earth’s climate. Recent satellite observations have further revealed a correlation between cosmic ray flux and low cloud top temperature. The temperature of a cloud depends on the radiation properties determined by its’ droplet distribution. Low clouds are warm (273K) and therefore consist of liquid water droplets. At typical tmospheric supersaturations (1%) a liquid cloud drop will only form in the presence of an aerosol, which acts as a condensation site. The roplet distribution of a cloud will then depend on the number of aerosols activated as cloud condensation nuclei (CCN) and the level of supersaturation. Based on observational evidence it is argued that a mechanism to explain the cosmic ray-cloud link might be found through the role of atmospheric ionisation in aerosol production and/or growth. Observations of local aerosol increases in low cloud due to ship exhaust indicate that a small perturbation in atmospheric aerosol can have a major impact on low cloud radiative properties. Thus, a moderate influence on atmospheric aerosol distributions from cosmic ray ionisation would have a strong influence on the Earth’s radiation budget. Historical evidence over the past 1000 years indicates that changes in climate have occurred in accord with variability in cosmic ray intensities. Such changes are in agreement with the sign of cloud radiative
forcing associated with cosmic ray variability as estimated from satellite observations.
The experiment indicates that ions play a role in nucleating new particles in the atmosphere and that the rate of production is sensitive to the ion density. If this sensitivity is still relevant at the size of cloud condensation nuclei, one might expect to find a relationship between ionization and cloud properties (Svensmark & Friis-Christensen 1997; Svensmark 1998; Shaviv 2002). Marsh & Svensmark (2000) found that the correlation between cosmic ray ionization and clouds is mainly in low-level clouds and not as might have been expected, in high clouds where ionization variations are large.
SYDNEY (Reuters) - Australian scientists have discovered a giant underwater current that is one of the last missing links of a system that connects the world's oceans and helps govern global climate.
New research shows that a current sweeping past Australia's southern island of Tasmania toward the South Atlantic is a previously undetected part of the world climate system's engine-room, said scientist Ken Ridgway.
The Southern Ocean, which swirls around Antarctica, has been identified in recent years as the main lung of global climate, absorbing a third of all carbon dioxide taken in by the world's oceans.
"We knew that they (deep ocean pathway currents) could move from the Pacific to the Indian Ocean through Indonesia. Now we can see that they move south of Tasmania as well, another important link," Ridgway, of the Commonwealth Scientific and Industrial Research Organization, told Reuters.
In each ocean, water flows around anticlockwise pathways, or gyres, the size of ocean basins.
The newly discovered Tasman Outflow, which sweeps past Tasmania at an average depth of 800-1,000 meters (2,600 to 3,300 feet), is classed as a "supergyre" that links the Indian, Pacific and Atlantic southern hemisphere ocean basins, the government-backed CSIRO said in a statement on Wednesday.
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SYDNEY (Reuters) - Australian scientists want to string a vast array of probes across the oceans of the southern hemisphere to warn of changes in ocean circulation that may affect the global climate.
The senior science adviser to the U.N.-backed World Climate Research Programme on Friday called for the establishment of a network of deep ocean moorings to extend a system already in operation in the northern hemisphere.
Instruments could be strung across the South Atlantic and through the Indonesian archipelago, as well as in the Southern Ocean where special designs would be necessary, said John Church of the government-backed Commonwealth Scientific and Industrial Research Organisation.
A North Atlantic moored network of scientific instruments already provides measurements of the northern "overturning circulation" conveyor belt of ocean currents, which forms a giant loop from the Gulf of Mexico to Iceland and back.
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