How Aerosols Contribute To Climate Change

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ScienceDaily (June 23, 2009) — What happens in Vegas may stay in Vegas, but what happens on the way there is a different story.

As imaged by Lynn Russell, a professor of atmospheric chemistry at Scripps Institution of Oceanography at UC San Diego, and her team, air blown by winds between San Diego and Las Vegas gives the road to Sin City a distinctive look.
The team has sampled air from the tip of the Scripps Pier since last year, creating a near real-time record of what kinds of particles — from sea salt to car exhaust — are floating around at any given time. Add data about wind speed and direction and the scientists can tell where particles came from and can map their pathways around Southern California.
When Russell and her students put it all together, the atmosphere of greater San Diego comes alive in colors representing the presence of different airborne chemical compounds in aerosol form. One streak of deep red draws a distinct line from the pier that sometimes extends all the way to Las Vegas. The red denotes organic mass, a carbon-based component of vehicular and industrial emissions that pops up on Russell’s readouts frequently. Plot the streak on a road atlas and it reveals the daily life of pollution in Southern California. For one stretch of time, it neatly traced Interstate 15 all the way past the California-Nevada border.
“We were really surprised,” said Russell. “We did not expect to have such consistent winds for the selected study days.”
The hunt for various types of aerosols is helping Russell draw new kinds of global maps, ones that depict what organic compounds—whether natural or from sources such as Southern California traffic and industries—could do to affect rainfall, snowfall, atmospheric warming and cooling, and a host of other climate phenomena. Russell is part of an effort that involves several researchers at Scripps and UCSD and around the world. Collectively they are attempting to address a human-caused phenomenon in the Earth system scarcely considered before the last decade.
Aerosol research is considered one of the most critical frontiers of climate change science, much of which is devoted to the creation of accurate projections of future climate. These projections are generated by computer models — simulations of phenomena such as warming patterns, sea level fluctuations, or drought trends. The raw data for the models can come from historical records of climate basics like temperature and precipitation, but scientists often must rely on incomplete data and best guesses to represent more complex phenomena. The more such uncertainty goes into a model, the greater its margin of error becomes, making it less reliable as a guide for forecasts and adaptive actions.
Among these complex phenomena, the actions of aerosols are what some researchers consider the field’s holy grail, representing the biggest barrier to producing accurate representations of climate. In fact, the Intergovernmental Panel on Climate Change in 2007 specifically listed the effect of aerosols on cloud formation as the largest source of uncertainty in present-day climate models.
Bits of dust, sea salt, the remnants of burned wood, and even living things like bacteria all add to the mix of aerosols that create the skeletons on which clouds form. Around these particles, water and ice condense and cluster into cloud masses. The size and number of each of these droplets determine whether the clouds can produce rain or snow.
The aerosols are also influencing climate in other ways. Diesel exhaust, industrial emissions, and the smoke from burning wood and brush eject myriad bits of black carbon, usually in the form of soot, into the sky and form so-called “brown clouds” of smog. This haze has a dual heating and cooling effect. The particles absorb heat and make the air warmer at the altitudes to which they tend to rise but they also deflect sunlight back into space. This shading effect cools the planet at ground level.
The Arctic Circle is one of the places in the world most sensitive to changes in the mix of aerosols. Since the beginnings of the Industrial Revolution, scientists and explorers have noted the presence of the Arctic haze, a swirl of pollution that appears when sunlight returns after a winter of darkness. The presence of smog over a mostly uninhabited region leads many scientists to believe it is the reason the Arctic is experiencing the most rapid climate-related changes in the world. The haze now lingers for a longer period of time every year. It may be contributing to the forces now causing a meltdown of Arctic ice, a release of methane once stored in permafrost, and a host of ecological changes affecting the spectrum of organisms from mosquitoes to polar bears.
Russell has taken part in two recent analyses of polar air to understand where its imported aerosols come from and how the chemical components of those aerosols could be affecting temperature and cloud formation. From a research vessel in the Norwegian Sea and via continuous measurements from a ground station in Barrow, Alaska, Russell’s team is analyzing particles likely to have been blown to the Arctic from Europe and Asia. Her group has just compiled a full season of air samples fed through intake valves onto filters collected at Barrow.
With it, she believes she has proven what colleagues have previously theorized about where the particles are coming from. She is especially interested in organic particles—aerosols containing carbon supplied either by natural sources such as ocean or land plants or by human sources. Work in her group has shown that organics in the spring haze carry a signature consistent with dust and biomass burning taking place most likely in Siberia. The chemical signature changes in other seasons, revealing itself in infrared spectroscopy readings to be the product of aerosols from natural sources.
The aerosols could be influencing how much snowfall the Arctic gets and keeps. Human-produced aerosols are thought to stifle precipitation in some areas but may provide the impetus for torrential rain in others depending on their chemical make-up. Even if the Asian aerosols are not affecting precipitation, however, Russell said they appear to cool the Arctic atmosphere by deflecting light into space. At the same time, there is strong evidence that they are accelerating ice melt in the Arctic by darkening and heating ice once they fall to the ground the way a dark sweater makes its wearer hotter on a sunny day than does a white sweater.
Russell has been part of another collaborative effort launched in 2008, the International Polar Year, that created chemical profiles of relatively untainted air off the Norwegian west coast, which is only occasionally tinged by European smog. She has also teamed with collaborators at Scripps, NOAA and other universities to profile aerosols around Houston, Texas, and Mexico City.
In the latter two projects, she has provided evidence that agriculture adds more to the aerosol mix in an oil town like Houston than previously thought and that organic particles in Mexico City, rising from the smoke of street vendors and exhaust of cars driving on gas formulated differently than in the United States, glom on to dust in a different manner than American pollution to create aerosols with distinct chemical structures. Figuring out what they do locally and regionally is the next step.
Russell collaborates with a number of other faculty at UCSD whose research also focuses on aerosols, such as Kim Prather, an atmospheric chemistry professor with joint appointments at Scripps and the UCSD Department of Chemistry and Biochemistry. Russell and Prather are comparing their results form Mexico City in an effort to better understand the sources of aerosols in the atmosphere.
“We are trying to understand the major sources of aerosols in our atmosphere and how they affect the overall temperature of our planet; as opposed to greenhouse gases which we know are warming, aerosols can cool or warm depending on their composition and where they are located in the atmosphere," said Prather. Like Russell, Prather also studies long-range transport of aerosols from terrestrial and marine sources. Prather and Russell have worked together on several other projects and recently helped form the Aerosol Chemistry and Climate Institute, a collaboration between Scripps and the Department of Energy’s Pacific Northwest National Laboratory.
For her most comprehensive study, Russell need only to make her shortest journey to the end of Scripps Pier. It is possible that aerosol journeys of a thousand miles or more might be explained by shorter commutes between Southern California counties. Complete analysis of the Interstate 15 data suggests Vegas might not be a source of dirtiness after all. Using data collected over longer time periods, Russell’s pollution map of local counties now suggests organic human-made aerosols might just be blowing toward Nevada from San Bernardino and Riverside then back toward San Diego as winds shift. Russell employs a suite of complementary measurements at the pier to characterize short- and long-term aerosol trends. Those are combined with particle profiles made by Prather’s group and collaborators whose numbers are growing out of necessity.
“Understanding the big picture is the only way we’re going to be able to reduce the uncertainty associated with aerosol particles and their effects on climate,” said Russell. “There are so many parameters, there’s no one instrument or even one person who can do all of it at once.”
Adapted from materials provided by University of California, San Diego, via Newswise.

Carbon Dioxide Higher Today Than Last 2.1 Million Years

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ScienceDaily (June 21, 2009) — Researchers have reconstructed atmospheric carbon dioxide levels over the past 2.1 million years in the sharpest detail yet, shedding new light on its role in the earth's cycles of cooling and warming.

The study, in the June 19 issue of the journal Science, is the latest to rule out a drop in CO2 as the cause for earth's ice ages growing longer and more intense some 850,000 years ago. But it also confirms many researchers' suspicion that higher carbon dioxide levels coincided with warmer intervals during the study period.
The authors show that peak CO2 levels over the last 2.1 million years averaged only 280 parts per million; but today, CO2 is at 385 parts per million, or 38% higher. This finding means that researchers will need to look back further in time for an analog to modern day climate change.
In the study, Bärbel Hönisch, a geochemist at Lamont-Doherty Earth Observatory, and her colleagues reconstructed CO2 levels by analyzing the shells of single-celled plankton buried under the Atlantic Ocean, off the coast of Africa. By dating the shells and measuring their ratio of boron isotopes, they were able to estimate how much CO2 was in the air when the plankton were alive. This method allowed them to see further back than the precision records preserved in cores of polar ice, which go back only 800,000 years.
The planet has undergone cyclic ice ages for millions of years, but about 850,000 years ago, the cycles of ice grew longer and more intense—a shift that some scientists have attributed to falling CO2 levels. But the study found that CO2 was flat during this transition and unlikely to have triggered the change.
"Previous studies indicated that CO2 did not change much over the past 20 million years, but the resolution wasn't high enough to be definitive," said Hönisch. "This study tells us that CO2 was not the main trigger, though our data continues to suggest that greenhouse gases and global climate are intimately linked."
The timing of the ice ages is believed to be controlled mainly by the earth's orbit and tilt, which determines how much sunlight falls on each hemisphere. Two million years ago, the earth underwent an ice age every 41,000 years. But some time around 850,000 years ago, the cycle grew to 100,000 years, and ice sheets reached greater extents than they had in several million years—a change too great to be explained by orbital variation alone.
A global drawdown in CO2 is just one theory proposed for the transition. A second theory suggests that advancing glaciers in North America stripped away soil in Canada, causing thicker, longer lasting ice to build up on the remaining bedrock. A third theory challenges how the cycles are counted, and questions whether a transition happened at all.
The low carbon dioxide levels outlined by the study through the last 2.1 million years make modern day levels, caused by industrialization, seem even more anomalous, says Richard Alley, a glaciologist at Pennsylvania State University, who was not involved in the research.
"We know from looking at much older climate records that large and rapid increase in CO2 in the past, (about 55 million years ago) caused large extinction in bottom-dwelling ocean creatures, and dissolved a lot of shells as the ocean became acidic," he said. "We're heading in that direction now."
The idea to approximate past carbon dioxide levels using boron, an element released by erupting volcanoes and used in household soap, was pioneered over the last decade by the paper's coauthor Gary Hemming, a researcher at Lamont-Doherty and Queens College. The study's other authors are Jerry McManus, also at Lamont; David Archer at the University of Chicago; and Mark Siddall, at the University of Bristol, UK.
Funding for the study was provided by the National Science Foundation.
Journal reference:
. Atmospheric Carbon Dioxide Concentrations Across the Mid-Pleistocene Transition. Science, June 19, 2009
Adapted from materials provided by The Earth Institute at Columbia University.

Maybe It's Raining Less Than We Thought: Physicists Make A Splash With Raindrops Discovery

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ScienceDaily (June 11, 2009) — It's conventional wisdom in atmospheric science circles: Large raindrops fall faster than smaller drops because they have a greater terminal speed -- i.e., the speed when the downward force of gravity is exactly the same as the upward air resistance.

Now two physicists from Michigan Technological University and colleagues at the Universidad Nacional Autónoma de México (National University of Mexico) have discovered that it ain't necessarily so.
Some smaller raindrops can fall faster than bigger ones. In fact, they can fall faster than their terminal speed. In other words, they can fall faster than drops that size and weight are supposed to be able to fall.
And that could mean that the weatherman has been overestimating how much it rains.
The findings of Michigan Tech physics professors Alexander Kostinski and Raymond Shaw—co-authors with Guillermo Montero-Martinez and Fernando Garcia-Garcia on a paper scheduled for publication online June 13, 2009, in the American Geophysical Union's journal Geophysical Research Letters—could improve the accuracy of weather measurement and prediction.
The researchers gathered data during natural rainfalls at the Mexico City campus of the National University of Mexico. They studied approximately 64,000 raindrops over three years, using optical array spectrometer probes and a particle analysis and collecting system. They also modified an algorithm or computational formula to analyze the raindrop sizes.
They found clusters of raindrops falling faster than their terminal speed, and as the rainfall became heavier, they saw more and more of these unexpectedly speedy drops. They think that the "super-terminal" drops come from the break-up of larger drops, which produces smaller fragments all moving at the same speed as their parent raindrop and faster than the terminal speed predicted by their size.
"In the past, people have seen indications of faster-than-terminal drops, but they always attributed it to splashing on the instruments," Shaw explains. He and his colleagues took special precautions to prevent such interference, including collecting data only during extremely calm conditions.
Their findings could significantly alter physicists' understanding of the physics of rain.
"Existing rain models are based on the assumption that all drops fall at their terminal speed, but our data suggest that this is not the case," Shaw and Kostinski say. If rainfall is measured based on that assumption, large raindrops that are not really there will be recorded.
"If we want to forecast weather or rain, we need to understand the rain formation processes and be able to accurately measure the amount of rain," Shaw pointed out.
Taking super-terminal raindrops into account could be of real economic benefit, even if it leads only to incremental improvements in precipitation measurement and forecasting. Approximately one-third of the economy—including agriculture, construction and aviation—is directly influenced by the ability to predict precipitation accurately. "And one-third of the economy is a very large sum of money, even during a recession," Shaw remarks.
The physicists' research was supported in part by the National Science Foundation.
Adapted from materials provided by Michigan Technological University.

Typhoons Trigger Slow Earthquakes

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ScienceDaily (June 12, 2009) — Scientists have made the surprising finding that typhoons trigger slow earthquakes, at least in eastern Taiwan. Slow earthquakes are non-violent fault slippage events that take hours or days instead of a few brutal seconds to minutes to release their potent energy. The researchers discuss their data in a study published the June 11, issue of Nature.

"From 2002 to 2007 we monitored deformation in eastern Taiwan using three highly sensitive borehole strainmeters installed 650 to 870 feet (200-270 meters) deep. These devices detect otherwise imperceptible movements and distortions of rock," explained coauthor Selwyn Sacks of Carnegie's Department of Terrestrial Magnetism. "We also measured atmospheric pressure changes, because they usually produce proportional changes in strain, which we can then remove."
Taiwan has frequent typhoons in the second half of each year but is typhoon free during the first 4 months. During the five-year study period, the researchers, including lead author Chiching Liu (Academia Sinica, Taiwan), identified 20 slow earthquakes that each lasted from hours to more than a day. The scientists did not detect any slow events during the typhoon-free season. Eleven of the 20 slow earthquakes coincided with typhoons. Those 11 were also stronger and characterized by more complex waveforms than the other slow events.
"These data are unequivocal in identifying typhoons as triggers of these slow quakes. The probability that they coincide by chance is vanishingly small," remarked coauthor Alan Linde, also of Carnegie.
How does the low pressure trigger the slow quakes? The typhoon reduces atmospheric pressure on land in this region, but does not affect conditions at the ocean bottom, because water moves into the area and equalizes pressure. The reduction in pressure above one side of an obliquely dipping fault tends to unclamp it. "This fault experiences more or less constant strain and stress buildup," said Linde. "If it's close to failure, the small perturbation due to the low pressure of the typhoon can push it over the failure limit; if there is no typhoon, stress will continue to accumulate until it fails without the need for a trigger."
"It's surprising that this area of the globe has had no great earthquakes and relatively few large earthquakes," Linde remarked. "By comparison, the Nankai Trough in southwestern Japan, has a plate convergence rate about 4 centimeters per year, and this causes a magnitude 8 earthquake every 100 to 150 years. But the activity in southern Taiwan comes from the convergence of same two plates, and there the Philippine Sea Plate pushes against the Eurasian Plate at a rate twice that for Nankai."
The researchers speculate that the reason devastating earthquakes are rare in eastern Taiwan is because the slow quakes act as valves, releasing the stress frequently along a small section of the fault, eliminating the situation where a long segment sustains continuous high stresses until it ruptures in a single great earthquake. The group is now expanding their instrumentation and monitoring for this research.
Adapted from materials provided by Carnegie Institution, via EurekAlert!, a service of AAAS.

Ancient Volcanic Eruptions Caused Global Mass Extinction

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ScienceDaily (May 30, 2009) — A previously unknown giant volcanic eruption that led to global mass extinction 260 million years ago has been uncovered by scientists at the University of Leeds.

The eruption in the Emeishan province of south-west China unleashed around half a million cubic kilometres of lava, covering an area 5 times the size of Wales, and wiping out marine life around the world.
Unusually, scientists were able to pinpoint the exact timing of the eruption and directly link it to a mass extinction event in the study published in Science. This is because the eruptions occurred in a shallow sea – meaning that the lava appears today as a distinctive layer of igneous rock sandwiched between layers of sedimentary rock containing easily datable fossilised marine life.
The layer of fossilised rock directly after the eruption shows mass extinction of different life forms, clearly linking the onset of the eruptions with a major environmental catastrophe.
The global effect of the eruption is also due to the proximity of the volcano to a shallow sea. The collision of fast flowing lava with shallow sea water caused a violent explosion at the start of the eruptions – throwing huge quantities of sulphur dioxide into the stratosphere.
"When fast flowing, low viscosity magma meets shallow sea it's like throwing water into a chip pan – there's spectacular explosion producing gigantic clouds of steam," explains Professor Paul Wignall, a palaeontologist at the University of Leeds, and the lead author of the paper.
The injection of sulphur dioxide into the atmosphere would have lead to massive cloud formation spreading around the world - cooling the planet and ultimately resulting in a torrent of acid rain. Scientists estimate from the fossil record that the environmental disaster happened at the start of the eruption.
"The abrupt extinction of marine life we can clearly see in the fossil record firmly links giant volcanic eruptions with global environmental catastrophe, a correlation that has often been controversial," adds Professor Wignall.
Previous studies have linked increased carbon dioxide produced by volcanic eruptions with mass extinctions. However, because of the very long term warming effect that occurs with increased atmospheric carbon dioxide (as we see with current climate change) the causal link between global environmental changes and volcanic eruptions has been hard to confirm.
This work was done in collaboration with the Chinese University of Geosciences in Wuhan and funded by a grant from the Natural Environment Research Council, UK.
Journal reference:
Paul B. Wignall, Yadong Sun, David P. G. Bond, Gareth Izon, Robert J. Newton, Stéphanie Védrine, Mike Widdowson, Jason R. Ali, Xulong Lai, Haishui Jiang, Helen Cope, and Simon H. Bottrell. Precise coincidence of explosive volcanism, mass extinction and carbon isotope fluctuations in the Middle Permian of China. Science, 2009; DOI: 10.1126/science.1171956
Adapted from materials provided by University of Leeds.

Ocean Circulation Doesn't Work As Expected

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This model of North Atlantic currents has been called into question by new data from Duke University and the Woods Hole Oceanographic Institution. Image: Archana Gowda, Duke
(PhysOrg.com) -- The familiar model of Atlantic ocean currents that shows a discrete "conveyor belt" of deep, cold water flowing southward from the Labrador Sea is probably all wet.

New research led by Duke University and the Woods Hole Oceanographic Institution relied on an armada of sophisticated floats to show that much of this water, originating in the sea between Newfoundland and Greenland, is diverted generally eastward by the time it flows as far south as Massachusetts. From there it disburses to the depths in complex ways that are difficult to follow.
A 50-year-old model of ocean currents had shown this southbound subsurface flow of cold water forming a continuous loop with the familiar northbound flow of warm water on the surface, called the Gulf Stream.
"Everybody always thought this deep flow operated like a conveyor belt, but what we are saying is that concept doesn't hold anymore," said Duke oceanographer Susan Lozier. "So it's going to be more difficult to measure these climate change signals in the deep ocean."
And since cold Labrador seawater is thought to influence and perhaps moderate human-caused climate change, this finding may affect the work of global warming forecasters.
"To learn more about how the cold deep waters spread, we will need to make more measurements in the deep ocean interior, not just close to the coast where we previously thought the cold water was confined," said Woods Hole's Amy Bower.
Lozier, a professor of physical oceanography at Duke's Nicholas School of the Environment and Bower, a senior scientist in the department of physical oceanography at the Woods Hole Institution, are co-principal authors of a report on the findings to be published in the May 14 issue of the research journal Nature.
Their research was supported by the National Science Foundation.
Climatologists pay attention to the Labrador Sea because it is one of the starting points of a global circulation pattern that transports cold northern water south to make the tropics a little cooler and then returns warm water at the surface, via the Gulf Stream, to moderate temperatures of northern Europe.

Since forecasters say effects of global warming are magnified at higher latitudes, that makes the Labrador Sea an added focus of attention. Surface waters there absorb heat-trapping carbon dioxide from the atmosphere. And a substantial amount of that CO2 then gets pulled underwater where it is no longer available to warm Earth's climate.
"We know that a good fraction of the human caused carbon dioxide released since the Industrial revolution is now in the deep North Atlantic" Lozier said. And going along for the ride are also climate-caused water temperature variations originating in the same Labrador Sea location.
The question is how do these climate change signals get spread further south? Oceanographers long thought all this Labrador seawater moved south along what is called the Deep Western Boundary Current (DWBC), which hugs the eastern North American continental shelf all the way to near Florida and then continues further south.
But studies in the 1990s using submersible floats that followed underwater currents "showed little evidence of southbound export of Labrador sea water within the Deep Western Boundary Current (DWBC)," said the new Nature report.
Scientists challenged those earlier studies, however, in part because the floats had to return to the surface to report their positions and observations to satellite receivers. That meant the floats' data could have been "biased by upper ocean currents when they periodically ascended," the report added.
To address those criticisms, Lozier and Bower launched 76 special Range and Fixing of Sound floats into the current south of the Labrador Sea between 2003 and 2006. Those "RAFOS" floats could stay submerged at 700 or 1,500 meters depth and still communicate their data for a range of about 1,000 kilometers using a network of special low frequency and amplitude seismic signals.
But only 8 percent of the RAFOS floats' followed the conveyor belt of the Deep Western Boundary Current, according to the Nature report. About 75 percent of them "escaped" that coast-hugging deep underwater pathway and instead drifted into the open ocean by the time they rounded the southern tail of the Grand Banks.
Eight percent "is a remarkably low number in light of the expectation that the DWBC is the dominant pathway for Labrador Sea Water," the researchers wrote.
Studies led by Lozier and other researchers had previously suggested cold northern waters might follow such "interior pathways" rather than the conveyor belt in route to subtropical regions of the North Atlantic. But "these float tracks offer the first evidence of the dominance of this pathway compared to the DWBC."
Since the RAFOS float paths could only be tracked for two years, Lozier, her graduate student Stefan Gary, and German oceanographer Claus Boning also used a modeling program to simulate the launch and dispersal of more than 7,000 virtual "efloats" from the same starting point.
"That way we could send out many more floats than we can in real life, for a longer period of time," Lozier said.
Subjecting those efloats to the same underwater dynamics as the real ones, the researchers then traced where they moved. "The spread of the model and the RAFOS float trajectories after two years is very similar," they reported.
"The new float observations and simulated float trajectories provide evidence that the southward interior pathway is more important for the transport of Labrador Sea Water through the subtropics than the DWBC, contrary to previous thinking," their report concluded.
"That means it is going to be more difficult to measure climate signals in the deep ocean," Lozier said. "We thought we could just measure them in the Deep Western Boundary Current, but we really can't."
Source: Duke University (news : web)

Changes In The Sun Are Not Causing Global Warming, New Study Shows

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ScienceDaily (May 12, 2009) — With the U.S. Congress beginning to consider regulations on greenhouse gases, a troubling hypothesis about how the sun may impact global warming is finally laid to rest.

Carnegie Mellon University's Peter Adams along with Jeff Pierce from Dalhousie University in Halifax, Canada, have developed a model to test a controversial hypothesis that says changes in the sun are causing global warming.
The hypothesis they tested was that increased solar activity reduces cloudiness by changing cosmic rays. So, when clouds decrease, more sunlight is let in, causing the earth to warm. Some climate change skeptics have tried to use this hypothesis to suggest that greenhouse gases may not be the global warming culprits that most scientists agree they are.
In research published in Geophysical Research Letters, and highlighted in the May 1 edition of Science, Adams and Pierce report the first atmospheric simulations of changes in atmospheric ions and particle formation resulting from variations in the sun and cosmic rays. They find that changes in the concentration of particles that affect clouds are 100 times too small to affect the climate.
"Until now, proponents of this hypothesis could assert that the sun may be causing global warming because no one had a computer model to really test the claims," said Adams, a professor of civil and environmental engineering at Carnegie Mellon.
"The basic problem with the hypothesis is that solar variations probably change new particle formation rates by less than 30 percent in the atmosphere. Also, these particles are extremely small and need to grow before they can affect clouds. Most do not survive to do so," Adams said.
Despite remaining questions, Adams and Pierce feel confident that this hypothesis should be laid to rest. "No computer simulation of something as complex as the atmosphere will ever be perfect," Adams said. "Proponents of the cosmic ray hypothesis will probably try to question these results, but the effect is so weak in our model that it is hard for us to see this basic result changing."
Journal references:
J. R. Pierce and P. J. Adams. Can cosmic rays affect cloud condensation nuclei by altering new particle formation rates? Geophys. Res. Lett., 2009; (in press) DOI: 10.1029/2009GL037946
Richard A. Kerr. Study Challenges Cosmic Ray-Climate Link. Science, 2009; 324 (5927): 576 DOI: 10.1126/science.324_576b
Adapted from materials provided by Carnegie Mellon University.

As Earth's air slowly trickles away into space, will our planet come to look like Venus?

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By Kevin J. Zahnle and David C. Catling

Many of the gases that make up Earth’s atmosphere and those of the other planets are slowly leaking into space. Hot gases, especially light ones, evaporate away; chemical reactions and particle collisions eject atoms and molecules; and asteroids and comets occasionally blast out chunks of atmosphere.
This leakage explains many of the solar system’s mysteries. For instance, Mars is red because its water vapor got broken down into hydrogen and oxygen, the hydrogen drifted away, and the surplus oxygen oxidized—in essence, rusted—the rocks. A similar process on Venus let carbon dioxide build up into a thick ocean of air; ironically, Venus’s huge atmosphere is the result of the loss of gases.

One of the most remarkable features of the solar system is the variety of planetary atmospheres. Earth and Venus are of comparable size and mass, yet the surface of Venus bakes at 460 degrees Celsius under an ocean of carbon dioxide that bears down with the weight of a kilometer of water. Callisto and Titan—planet-size moons of Jupiter and Saturn, respectively—are nearly the same size, yet Titan has a nitrogen-rich atmosphere thicker than our own, whereas Callisto is essentially airless. What causes such extremes? If we knew, it would help explain why Earth teems with life while its planetary siblings appear to be dead. Knowing how atmospheres evolve is also essential to determining which planets beyond our solar system might be habitable.
A planet can acquire a gaseous cloak in many ways: it can release vapors from its interior, it can capture volatile materials from comets and asteroids when they strike, and its gravity can pull in gases from interplanetary space. But planetary scientists have begun to appreciate that the escape of gases plays as big a role as the supply. Although Earth’s atmosphere may seem as permanent as the rocks, it gradually leaks back into space. The loss rate is currently tiny, only about three kilograms of hydrogen and 50 grams of helium (the two lightest gases) per second, but even that trickle can be significant over geologic time, and the rate was probably once much higher. As Benjamin Franklin wrote, “A small leak can sink a great ship.” The atmospheres of terrestrial planets and outer-planet satellites we see today are like the ruins of medieval castles—remnants of riches that have been subject to histories of plunder and decay. The atmospheres of smaller bodies are more like crude forts, poorly defended and extremely vulnerable.
Recognizing the importance of atmospheric escape changes our perspective on the solar system. For decades, scientists have pondered why Mars has such a thin atmosphere, but now we wonder: Why does it have any atmosphere left at all? Is the difference between Titan and Callisto a consequence of Callisto’s losing its atmosphere, rather than of Titan having been born of airier stuff? Was Titan’s atmosphere once even thicker than it is today? How did Venus steadfastly cling to its nitrogen and carbon dioxide yet thoroughly lose its water? Did escape of hydrogen help to set the stage for complex life on Earth? Will it one day turn our planet into another Venus?
When the Heat Is OnA spaceship that reaches escape velocity is moving fast enough to break free of a planet’s gravity. The same is true of atoms and molecules, although they usually reach escape velocity less purposefully. In thermal escape, gases get too hot to hold on to. In nonthermal processes, chemical or charged-particle reactions hurl out atoms and molecules. And in a third process, asteroid and comet impacts blast away the air.
Thermal escape is, in some ways, the most common and straightforward of the three. All bodies in the solar system are heated by sunlight. They rid themselves of this heat in two ways: by emitting infrared radiation and by shedding matter. In long-lived bodies such as Earth, the former process prevails; for others, such as comets, the latter dominates. Even a body the size of Earth can heat up quickly if absorption and radiation get out of balance, and its atmosphere—which typically has very little mass compared with the rest of the planet—can slough off in a cosmic instant. Our solar system is littered with airless bodies, and thermal escape seems to be a common culprit. Airless bodies stand out as those where solar heating exceeds a certain threshold, which depends on the strength of the body’s gravity [Purchase the digital edition to see related sidebar].
Thermal escape occurs in two ways. In the first, called Jeans escape, after James Jeans, the English astronomer who described it in the early 20th century, air literally evaporates atom by atom, molecule by molecule, off the top of the atmosphere. At lower altitudes, collisions confine particles, but above a certain altitude, known as the exobase, which on Earth is about 500 kilometers above the surface, air is so tenuous that gas particles hardly ever collide. Nothing stops an atom or molecule with sufficient velocity from flying away into space.

As the lightest gas, hydrogen is the one that most easily overcomes a planet’s gravity. But first it must reach the exobase, and on Earth that is a slow process. Hydrogen-bearing molecules tend not to rise above the lowest layer of atmosphere: water vapor (H2O) condenses out and rains back down, and methane (CH4) is oxidized to form carbon dioxide (CO2). Some water and methane molecules reach the stratosphere and decompose, releasing hydrogen, which slowly diffuses upward until it reaches the exobase. A small amount clearly makes it out because ultraviolet images reveal a halo of hydrogen atoms surrounding our planet [Purchase the digital edition to see related sidebar].
The temperature at Earth’s exobase oscillates but is typically about 1,000 kelvins, implying that hydrogen atoms have an average speed of five kilometers per second. That is less than Earth’s escape velocity at that altitude, 10.8 kilometers per second, but the average conceals a wide range, so some hydrogen atoms still manage to break free of our planet’s gravity. This loss of particles from the energetic tail of the speed distribution explains about 10 to 40 percent of Earth’s hydrogen loss today. Jeans escape also partly explains why our moon is airless. Gases released from the lunar surface easily evaporate off into space.
A second type of thermal escape is far more dramatic. Whereas Jeans escape occurs when a gas evaporates molecule by molecule, heated air can also flow en masse. The upper atmosphere can absorb ultraviolet sunlight, warm up and expand, pushing air upward. As the air rises, it accelerates smoothly through the speed of sound and then attains the escape velocity. This form of thermal escape is called hydrodynamic escape or, more evocatively, the planetary wind—the latter by analogy to the solar wind, the stream of charged particles blown from the sun into interplanetary space.
Dust in the WindAtmospheres rich with hydrogen are the most vulnerable to hydrodynamic escape. As hydrogen flows outward, it can pick up and drag along heavier molecules and atoms with it. Much as the desert wind blows dust across an ocean and sand grains from dune to dune, while leaving cobbles and boulders behind, the hydrogen wind carries off molecules and atoms at a rate that diminishes with their weight. Thus, the present composition of an atmosphere can reveal whether this process has ever occurred.
In fact, astronomers have seen the telltale signs of hydrodynamic escape outside the solar system, on the Jupiter-like planet HD 209458b. Using the Hubble Space Telescope, Alfred Vidal-Madjar of the Paris Astrophysics Institute and his colleagues reported in 2003 that the planet has a puffed-up atmosphere of hydrogen. Subsequent measurements discovered carbon and oxygen in this inflated atmosphere. These atoms are too heavy to escape on their own, so they must have been dragged there by hydrogen. Hydrodynamic loss would also explain why astronomers find no large planets much closer to their stars than HD 209458b is. For planets that orbit within three million kilometers or so of their stars (about half the orbital radius of HD 209458b), hydrodynamic escape strips away the entire atmosphere within a few billion years, leaving behind only a scorched remnant.
This evidence for planetary winds lends credence to ideas put forth in the 1980s about hydrodynamic escape from ancient Venus, Earth and Mars. Three clues suggest this process once operated on these worlds. The first concerns noble gases. Were it not for escape, chemically unreactive gases such as neon or argon would remain in an atmosphere indefinitely. The abundances of their different isotopes would be similar to their original values, which in turn are similar to that of the sun, given their common origin in the solar nebula. Yet the abundances differ.
Second, youthful stars are strong sources of ultraviolet light, and our sun was probably no exception. This radiation could have driven hydrodynamic escape.

Third, the early terrestrial planets may have had hydrogen-rich atmospheres. The hydrogen could have come from chemical reactions of water with iron, from nebular gases or from water molecules broken apart by solar ultraviolet radiation. In those primeval days, asteroids and comets hit more frequently, and whenever they smacked into an ocean, they filled the atmosphere with steam. Over thousands of years the steam condensed and rained back onto the surface, but Venus is close enough to the sun that water vapor may have persisted in the atmosphere, where solar radiation could break it down.
Under such conditions, hydrodynamic escape would readily operate. In the 1980s James F. Kasting, now at Pennsylvania State University, showed that hydrodynamic escape on Venus could have carried away an ocean’s worth of hydrogen within a few tens of millions of years [see “How Climate Evolved on the Terrestrial Planets,” by James F. Kasting, Owen B. Toon and James B. Pollack; Scientific American, February 1988]. Kasting and one of us (Zahnle) subsequently showed that escaping hydrogen would have dragged along much of the oxygen but left carbon dioxide behind. Without water to mediate the chemical reactions that turn carbon dioxide into carbonate minerals such as limestone, the carbon dioxide built up in the atmosphere and created the hellish Venus we see today.
To a lesser degree, Mars and Earth, too, appear to have suffered hydrodynamic losses. The telltale signature is a deficit of lighter isotopes, which are more easily lost. In the atmospheres of Earth and Mars, the ratio of neon 20 to neon 22 is 25 percent smaller than the solar ratio. On Mars, argon 36 is similarly depleted relative to argon 38. Even the isotopes of xenon—the heaviest gas in Earth’s atmosphere apart from pollutants—show the imprint of hydrodynamic escape. If hydrodynamic escape were vigorous enough to sweep up xenon, why did it not sweep up everything else in the atmosphere along with it? To solve this puzzle, we may need to construct a different history for xenon than for the other gases now in the atmosphere.
Hydrodynamic escape may have stripped Titan of much of its air, too. When it descended through Titan’s atmosphere in 2005, the European Space Agency’s Huygens probe found that the ratio of nitrogen 14 to nitrogen 15 is 70 percent of that on Earth. That is a huge disparity given that the two isotopes differ only slightly in their tendency to escape. If Titan’s atmosphere started with the same nitrogen isotopic composition as Earth’s, it must have lost a huge amount of nitrogen—several times the substantial amount it currently has—to bring the ratio down to its present value. In short, Titan’s atmosphere might once have been even thicker than it is today, which only heightens its mystery.
Better Escaping through ChemistryOn some planets, including modern Earth, thermal escape is less important than nonthermal escape. In nonthermal escape, chemical reactions or particle-particle collisions catapult atoms to escape velocity. What nonthermal escape mechanisms have in common is that an atom or molecule reaches a very high velocity as the outcome of a single event that takes place above the exobase, so that bumping into something does not thwart the escapee. Many types of nonthermal escape involve ions. Ordinarily these charged particles are tethered to a planet by its magnetic field, either the global (internally generated) magnetic field—if there is one—or the localized fields induced by the passage of the solar wind. But they find ways to slip out.
In one type of event, known as charge exchange, a fast hydrogen ion collides with a neutral hydrogen atom and captures its electron. The result is a fast neutral atom, which is immune to the magnetic field. This process accounts for 60 to 90 percent of the present loss of hydrogen from Earth and most of the hydrogen loss from Venus.

Another way out exploits a weak spot—dare we say a loophole—in the planet’s magnetic trap. Most magnetic field lines loop from one magnetic pole to the other, but the widest field lines are dragged outward by the solar wind and do not loop back; they remain open to interplanetary space. Through this opening, ions can escape. To be sure, the ions must still overcome gravity, and only the lightest ions such as hydrogen and helium make it. The resulting stream of charged particles, called the polar wind (not to be confused with the planetary wind), accounts for 10 to 15 percent of Earth’s hydrogen loss and almost its entire helium leak.
In some cases, these light ions can sweep up heavier ions with them. This process may explain the xenon puzzle: if the polar wind was more vigorous in the past, it could have dragged out xenon ions. One piece of evidence is that krypton does not have the same isotopic pattern as xenon does, even though it is a lighter gas and, all else being equal, ought to be more prone to escape. The difference is that krypton, unlike xenon, resists ionization, so even a strong polar wind would have left it unaffected.
A third nonthermal process known as photochemical escape operates on Mars and possibly on Titan. Oxygen, nitrogen and carbon monoxide molecules drift into the upper atmosphere, where solar radiation ionizes them. When the ionized molecules recombine with electrons or collide with one another, the energy released splits the molecules into atoms with enough speed to escape.
Mars, Titan and Venus lack global magnetic fields, so they are also vulnerable to a fourth nonthermal process known as sputtering. Without a planetary field to shield it, the upper atmosphere of each of these worlds is exposed to the full brunt of the solar wind. The wind picks up ions, which then undergo charge exchange and escape. Mars’s atmosphere is enriched in heavy nitrogen and carbon isotopes, suggesting that it has lost as much as 90 percent of an earlier atmosphere. Sputtering and photochemical escape are the most likely culprits. In 2013 NASA plans to launch the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to measure escaping ions and neutral atoms and reconstruct the planet’s atmospheric history.
Inescapable ConsequencesBoth thermal and nonthermal escape are like tiny trickles compared with the huge splash when comets or asteroids crash into planets. If projectiles are sufficiently big and fast, they vaporize both themselves and a similar mass of the surface. The ensuing hot gas plume can expand faster than the escape velocity and drive off the overlying air. The larger the impact energy, the wider the cone of atmosphere ejected. For the asteroid that killed off the dinosaurs 65 million years ago, the cone was about 80 degrees wide from the vertical and contained a hundred-thousandth of the atmosphere. An even more energetic impact can carry away the entire atmosphere above a plane that is tangent to the planet.
Another factor determining the width of the cone is the atmospheric density. The thinner the air, the greater the fraction of the atmosphere that gets lost. The implication is gloomy: once a vulnerable atmosphere starts wearing away, impact erosion becomes ever easier until the atmosphere vanishes altogether. Unfortunately, Mars spent its youth in a bad neighborhood near the asteroid belt and, being small, was especially susceptible. Given the expected size distribution of impactors early in a solar system’s history, the planet should have been stripped of its entire atmosphere in less than 100 million years.
The large moons of Jupiter also live in a dangerous neighborhood—namely, deep in the giant planet’s gravitational field, which accelerates incoming asteroids and comets. Impacts would have denuded these moons of any atmospheres they ever had. In contrast, Titan orbits comparatively far from Saturn, where impact velocities are slower and an atmosphere can survive.

In all these ways, escape accounts for much of the diversity of atmospheres, from the lack of air on Callisto and Ganymede to the absence of water on Venus. A more subtle consequence is that escape tends to oxidize planets, because hydrogen is lost more easily than oxygen. Hydrogen escape is the ultimate reason why Mars, Venus and even Earth are red. Most people do not think of Earth as a red planet, but much of the continental crust is red. Soil and vegetation hide this native hue. All three worlds started out the gray-black color of volcanic rock and reddened as the original minerals oxidized to iron oxides (similar to rust). To account for its color, Mars must have lost an ocean of water equivalent to a global layer meters to tens of meters deep.
On Earth, most researchers attribute the accumulation of oxygen 2.4 billion years ago to photosynthetic organisms, but in 2001 we suggested that the escape of hydrogen also played an important role. Microbes break apart water molecules in photosynthesis, and the hydrogen can pass like a baton from organic matter to methane and eventually reach space. The expected amount of hydrogen loss matches the net excess of oxidized material on Earth today.
Escape helps to solve the mystery of why Mars has such a thin atmosphere. Scientists have long hypothesized that chemical reactions among water, carbon dioxide and rock turned the original thick atmosphere into carbonate minerals. The carbonates were never recycled back into carbon dioxide gas because Mars, being so small, cooled quickly and its volcanoes stopped erupting. The trouble with this scenario is that spacecraft have so far found only a single small area on Mars with carbonate rock, and this outcrop probably formed in warm subsurface waters. Moreover, the carbonate theory offers no explanation for why Mars has so little nitrogen or noble gases. Escape provides a better answer. The atmosphere did not get locked away as rock; it dissipated into space.
A nagging problem is that impact erosion ought to have removed Mars’s atmosphere altogether. What stopped it? One answer is simple chance. Large impacts are inherently rare, and their frequency fell off rapidly about 3.8 billion years ago, so Mars may have been spared the final devastating blow. A large impact of an icy asteroid or comet could have deposited more volatiles than subsequent impacts could remove. Alternatively, remnants of Mars’s atmosphere may have survived underground and leaked out after the bombardment had subsided.
Although Earth seems comparatively unscathed by escape, that will change. Today hydrogen escape is limited to a trickle because the principal hydrogen-bearing gas, water vapor, condenses in the lower atmosphere and rains back to the surface. But our sun is slowly brightening at about 10 percent every billion years. That is imperceptibly slow on a human timescale but will be devastating over geologic time. As the sun brightens and our atmosphere warms, the atmosphere will get wetter, and the trickle of hydrogen escape will become a torrent.
This process is expected to become important when the sun is 10 percent brighter—that is, in a billion years—and it will take another billion years or so to desiccate our planet’s oceans. Earth will become a desert planet, with at most a shrunken polar cap and only traces of precious liquid. After another two billion years, the sun will beat down on our planet so mercilessly even the polar oases will fail, the last liquid water will evaporate and the greenhouse effect will grow strong enough to melt rock. Earth will have followed Venus into a barren lifelessness.
This story was originally printed with the title "The Planetary Air Leak"
ABOUT THE AUTHOR(S)Planetary scientist David C. Catling studies the coupled evolution of planetary surfaces and atmospheres. Formerly at the NASA Ames Research Center, he joined the faculty at the University of Washington in 2001. He is a co- investigator for NASAs Phoenix lander, which completed its mission last December. Kevin J. Zahnle has been a research scientist at the NASA Ames center since 1989. Even by the eclectic standards of planetary science, he has an unusually wide range of interests, from planetary interiors to surfaces to atmospheres. In 1996 Zahnle received the NASA Exceptional Achievement Medal for his work on the impact of Comet Shoemaker-Levy 9 into Jupiter.

Deep Earth Model Challenged By New Experiment

Source:

http://www.sciencedaily.com/releases/2007/09/070920145537.htm

Science Daily — In the first experiments able to mimic the crushing, searing conditions found in Earth's lower mantle, and simultaneously probe tell-tale properties of iron, scientists* have discovered that material there behaves very differently than predicted by models. The research also points to the likelihood of a new zone deep in the Earth.

Surface phenomena such as volcanoes and earthquakes are generated by what goes on in Earth's interior. To understand some of these surface dynamics, scientists have to probe deep into the planet. The lower mantle is between 400 and 1,740 miles deep (650 km- 2,800 km) and sits atop the outer core.
Coauthor of the paper, Viktor Struzhkin of the Carnegie Institution's Geophysical Laboratory explains: "The deeper you go, the higher the pressures and temperatures become. Under these extreme conditions, the atoms and electrons of the rocks become squeezed so close together that they interact very peculiarly. In fact, spinning electrons in iron, which is prevalent throughout the inner Earth, are forced to pair up. When this spin state changes from unpaired electrons--called a high-spin state--to paired electrons--a low-spin state--the density, sound velocities, conductivity, and other properties of the materials can change. Understanding these conditions helps scientists piece together the complex puzzle of the interior/surface interactions."
The pressures in the lower mantle are brutal, ranging from about 230,000 times the atmospheric pressure at sea level (23 GPa), to almost 1.35 million times sea-level pressure (135 GPa). The heat is equally extreme--from about 2,800 to 6,700 degrees Fahrenheit (1800 K--4000 K).
Using a laser-heated diamond anvil cell to heat and compress the samples, the scientists subjected ferropericlase to almost 940,000 atmospheres and 3,140 °F. They analyzed it using so-called X-ray emission spectroscopy. As its name suggests, ferropericlase is iron-laden.
It is also the second most prevalent material found in the lower mantle. Previous to this study, ferropericlase has been subjected to high pressures, but only to room temperatures. The new experiments are the highest pressures and temperatures attained to probe the spin state of iron in the mineral at lower-mantle conditions.
Under the less-intense conditions of the former experiments, the high-spin to low-spin transition occurs in a narrow pressure range. In the new study, however, both spin states coexisted in the same crystal structure and the spin transition was also continuous over a large pressure range, indicating that the mineral is in a complex state over a large range in depth in the planet.
"We were expecting to find a transition zone, but did not know how extended it may be in the Earth's mantle," commented Struzhkin. "Our findings suggest that there is a region or 'spin-transition zone' from about 620 miles to 1,365 miles deep, where high spin, unpaired electrons, transition to low spin, paired electrons. The transitioning appears to be continuous over these depths. At pressures representing a lower depth of about 1,365 miles the transition stops and ferropericlase is dominated by low-spin electrons."
Since measurements that scientists use to determine the composition and density of the inner Earth, such as sound velocities, are influenced by the ratio of high-spin/low- spin states, the new finding calls into question the traditional techniques for modeling this region of the planet.
In addition, a continuous spin transition zone may explain some interesting experimental findings including why there has been no significant iron partitioning, or separating, into ferropericlase or perovskite, the most prevalent mineral in the region. The research also suggests that the depth of the transition zone is less than scientists had speculated.
The existence of this transition zone may also account for seismic-wave behavior at those depths. The fact that the lowermost area is dominated by denser low-spin material could also affect the temperature stability of mantle upwellings--the generators of volcanic hotspots, such as those in Hawaii.
"This paper solves only part of the puzzle," cautioned Struzhkin. "Since the major lower mantle mineral perovskite has not been measured yet with this technique, we know there are more surprises to come."
"The spin transition zone of iron needs to be considered in future models of the lower mantle," said Choong-Shik Yoo, a former staff member at LLNL and now a professor at Washington State University. "In the past, geophysicists had neglected the effects of the spin transition when studying the Earth's interior.
Since we identified this zone, the next step is to study the properties of lower mantle oxides and silicates across the zone. This research also calls for future seismic and geodynamic tests in order to understand the properties of the spin transition zone."
"The benchmark techniques developed here have profound implications for understanding the electronic transitions in lanthanoid and actinoid compounds under extreme conditions because their properties would be affected by the electronic transitions," said Valentin Iota, a staff member in LLNL's Physics and Advanced Technologies Directorate.
The work is published in the September 21, 2007, issue of Science.
*Authors on this paper are Jung-Fu Lin, Lawrence Livermore National Laboratory (LLNL); György Vankó, KFKI Research Institute for Particle and Nuclear Physics and the European Synchrotron Radiation Facility; Steven Jacobsen, Northwestern University; Viktor Struzhkin, Carnegie Institution's Geophysical Laboratory; Vitali Prakapenka, University of Chicago; Alexie Kuznetsov, University of Chicago; and Choong-Shik Yoo LLNL.
Note: This story has been adapted from a news release issued by Carnegie Institution.

Fausto Intilla

www.oloscience.com

Northwest Passage Opens: Arctic Sea Ice Reaches New Low

Source:

http://www.sciencedaily.com/releases/2007/09/070914095358.htm

Science Daily — The area covered by sea ice in the Arctic has now (September 14, 2007) shrunk to its lowest level since satellite measurements began nearly 30 years ago, opening up the Northwest Passage – a long-sought short cut between Europe and Asia that has been historically impassable.

Leif Toudal Pedersen from the Danish National Space Centre said: "We have seen the ice-covered area drop to just around 3 million sq km which is about 1 million sq km less than the previous minima of 2005 and 2006. There has been a reduction of the ice cover over the last 10 years of about 100 000 sq km per year on average, so a drop of 1 million sq km in just one year is extreme.
"The strong reduction in just one year certainly raises flags that the ice (in summer) may disappear much sooner than expected and that we urgently need to understand better the processes involved."
Arctic sea ice naturally extends its surface coverage each northern winter and recedes each northern summer, but the rate of overall loss since 1978 when satellite records began has accelerated.
The most direct route of the Northwest Passage across northern Canada is now fully navigable, while the Northeast Passage along the Siberian coast remains only partially blocked. To date, the Northwest Passage has been predicted to remain closed even during reduced ice cover by multi-year ice pack – sea ice that survives one or more summers. However, according to Pedersen, this year’s extreme event has shown the passage may well open sooner than expected.
The previous record low was in 2005 when the Arctic area covered by sea ice was just 4 million sq km. Even then, the most direct Northwest Passage did not fully open.
The Polar Regions are very sensitive indicators of climate change. The UN’s Intergovernmental Panel on Climate Change showed these regions are highly vulnerable to rising temperatures and predicted the Arctic would be virtually ice free by the summer of 2070. Still other scientists predict it could become ice free as early as 2040 due to rising temperatures and sea ice decline.
Because sea ice has a bright surface, the majority of solar energy that hits it is reflected back into space. When sea ice melts, the dark-coloured ocean surface is exposed. Solar energy is then absorbed rather than reflected, so the oceans get warmer and temperatures rise, making it difficult for new ice to form.
The Arctic is one of Earth’s most inaccessible areas, so obtaining measurements of sea ice was difficult before the advent of satellites. For more than 20 years, ESA has been providing satellite data to the cryosphere communities. Currently, ESA is contributing to the International Polar Year (IPY) – a large worldwide science programme focused on the Arctic and Antarctic.
Since 2006, ESA has supported Polar View, a satellite remote-sensing programme funded through the Earthwatch GMES Service Element (GSE) that focuses on the Arctic and the Antarctic.
In 2009, ESA will make another significant contribution to cryosphere research with the launch of CryoSat-2. The observations made over the three-year lifetime of the mission will provide conclusive evidence on the rates at which ice cover is diminishing.
Note: This story has been adapted from a news release issued by European Space Agency.

Fausto Intilla

www.oloscience.com

Global Warming Will Bring Violent Storms And Tornadoes, NASA Predicts

Source:

http://www.sciencedaily.com/releases/2007/08/070830105911.htm

Science Daily — NASA scientists have developed a new climate model that indicates that the most violent severe storms and tornadoes may become more common as Earth's climate warms.

Previous climate model studies have shown that heavy rainstorms will be more common in a warmer climate, but few global models have attempted to simulate the strength of updrafts in these storms. The model developed at NASA's Goddard Institute for Space Studies by researchers Tony Del Genio, Mao-Sung Yao, and Jeff Jonas is the first to successfully simulate the observed difference in strength between land and ocean storms and is the first to estimate how the strength will change in a warming climate, including "severe thunderstorms" that also occur with significant wind shear and produce damaging winds at the ground.
This information can be derived from the temperatures and humidities predicted by a climate computer model, according to the new study published on August 17 in the American Geophysical Union's Geophysical Research Letters. It predicts that in a warmer climate, stronger and more severe storms can be expected, but with fewer storms overall.
Global computer models represent weather and climate over regions several hundred miles wide. The models do not directly simulate thunderstorms and lightning. Instead, they evaluate when conditions are conducive to the outbreak of storms of varying strengths. This model first was tested against current climate conditions. It was found to represent major known global storm features including the prevalence of lightning over tropical continents such as Africa and, to a lesser extent, the Amazon Basin, and the near absence of lightning in oceanic storms.
The model then was applied to a hypothetical future climate with double the current carbon dioxide level and a surface that is an average of 5 degrees Fahrenheit warmer than the current climate. The study found that continents warm more than oceans and that the altitude at which lightning forms rises to a level where the storms are usually more vigorous.
These effects combine to cause more of the continental storms that form in the warmer climate to resemble the strongest storms we currently experience.
Lightning produced by strong storms often ignites wildfires in dry areas. Researchers have predicted that some regions would have less humid air in a warmer climate and be more prone to wildfires as a result. However, drier conditions produce fewer storms. "These findings may seem to imply that fewer storms in the future will be good news for disastrous western U.S. wildfires," said Tony Del Genio, lead author of the study and a scientist at NASA's Goddard Institute for Space Studies, New York. "But drier conditions near the ground combined with higher lightning flash rates per storm may end up intensifying wildfire damage instead."
The central and eastern areas of the United States are especially prone to severe storms and thunderstorms that arise when strong updrafts combine with horizontal winds that become stronger at higher altitudes. This combination produces damaging horizontal and vertical winds and is a major source of weather-related casualties. In the warmer climate simulation there is a small class of the most extreme storms with both strong updrafts and strong horizontal winds at higher levels that occur more often, and thus the model suggests that the most violent severe storms and tornadoes may become more common with warming.
The prediction of stronger continental storms and more lightning in a warmer climate is a natural consequence of the tendency of land surfaces to warm more than oceans and for the freezing level to rise with warming to an altitude where lightning-producing updrafts are stronger. These features of global warming are common to all models, but this is the first climate model to explore the ramifications of the warming for thunderstorms.
Note: This story has been adapted from a news release issued by NASA/Goddard Space Flight Center.

Fausto Intilla

www.oloscience.com