Climate Models Miss Effects of Wind-Shattered Dust

Clumps of dust in the desert shatter like glass on a kitchen floor. This similarity may mean the atmosphere carries more large dust particles than climate models assume.

Dust and other airborne particles’ effect in the atmosphere is “one of the most important problems we need to solve in order to provide better predictions of climate,” said climate scientist Jasper Kok of the National Center for Atmospheric Research in Boulder, Colorado. Other researchers suspect current models also neglect a large fraction of the climate-warming dust that clogs the skies after dust storms.

Most climate models use dust data from satellites that measure how many particles of different sizes are suspended in the atmosphere. These measurements reveal an abundance of tiny clay particles roughly 2 micrometers across (about one-third the width of a red blood cell), which can reflect sunlight back into space and cool the planet.

But satellites may be missing larger particles, called silts, which don’t hang around in the air as long. Silts up to 20 micrometers in diameter can act as a warm blanket to trap heat inside the Earth’s atmosphere.

To figure out how much clay and silt is actually kicked up from the Earth’s deserts, Kok turned to a well-studied problem in physics: how glass breaks.

Cracks spread through breaking glass in specific patterns, creating predictable numbers and sizes of glass shards. The final distribution of small, medium and large glass fragments follows a mathematical law called scale invariance.

“It shows up all across nature, from asteroids to atomic nuclei,” Kok said. “It’s really just beautiful.”

In a paper published Dec. 28 in the Proceedings of the National Academy of Sciences, Kok showed that the physics of how dust clumps break apart is similar to glass breaking.

Soil scientists have long known that dust clumps act like brittle materials, and physicists have well-tested mathematical descriptions of how brittle materials break. “But no one had put one and two together,” Kok said.

When wind picks up in the desert, Kok says, the particles that move first are large sand particles, up to 500 micrometers across. Silt-sized and smaller dust grains tend to stick together until a bouncing sand particle smacks into them.

“It’s physically analogous to hitting your windshield with a hammer, or dropping a drinking glass on the kitchen floor,” Kok said.

Cracks spread through the clump of soil as they would through a pane of glass, sending the same fraction of small, medium and large particles bouncing into the atmosphere. Kok compared his theory to ground measurements made in the middle of dust storms in six locations around the world and found they matched perfectly.

“Even though we don’t have an abundance of measurements, I think we have sufficient measurements to say this theory is a step in the right direction,” Kok said.

Kok’s theory suggests that dust storms produce two to eight times more silt-sized particles than climatologists previously thought. Neglecting the boost in particles suggests that climate models, and even short-term weather models for dusty regions, are somewhat off. Until climate scientists better understand how dust changes over time, however, Kok said it’s tough to gauge the effects.

“I thought it was a breakthrough, a real original idea,” said atmospheric physicist Charles Zender of the University of California at Irvine, who was not involved in the new work. Similarities to fractured glass may show up in other earth science systems, like earthquakes or glacier calving, he added. “Whether it’s submicron and invisible to the human eye, or as large as Greenland, it doesn’t matter. It’s the same property.”

Dust expert Tom Gill of the University of Texas at El Paso thinks Kok’s theory is elegant, though it will have to be backed up by lab and field experiments. If it holds up, however, “it has the potential to make some real improvements in modeling how dust and dust-like things move around and disperse and fall out of the air. That has implications for everything from global climate to volcanoes to hurricanes,” he said. “I’m very encouraged by it.”

By Lisa Grossman 
From wired.com

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Climate Change Authority Admits Mistake

One of the most alarming conclusions from the Intergovernmental Panel on Climate Change (IPCC), a widely respected organization established by the United Nations, is that glaciers in the Himalayas could be gone 25 years from now, eliminating a primary source of water for hundreds of millions of people. But a number of glaciologists have argued that this conclusion is wrong, and now the IPCC admits that the conclusion is largely unsubstantiated, based on news reports rather than published, peer-reviewed scientific studies.

Still there: The Khumbu glacier, in front of Mount Everest, is one of the longest glaciers in the world. Though the Himalayan glaciers are being affected by global warming, they won’t disappear in 25 years, as the authors of a recent report by the Intergovernmental Panel on Climate Change incorrectly predicted.

In a statement released on Wednesday, the IPCC admitted that the Working Group II report, "Impacts, Adaptation and Vulnerability," published in the IPCC's Fourth Assessment Report (2007), contains a claim that "refers to poorly substantiated estimates. " The statement also said "the clear and well-established standards of evidence, required by the IPCC procedure, were not applied properly." The statement did not quote the error, but it did cite the section of the report that refers to Himalayan glaciers. Christopher Field, director of the Carnegie Institution's Department of Global Ecology, who is now in charge of Working Group II, confirms that the error was related to the claim that the glaciers could disappear by 2035.

The disappearance of the glaciers would require temperatures far higher than those predicted in even the most dire global warming scenarios, says Georg Kaser, professor at the Institut für Geographie der Universität, Innsbruck. The Himalayas would have to heat up by 18 degrees Celsius and stay there for the highest glaciers to melt--most climate change scenarios expect only a few degrees of warming over the next century.

The mistake has called into question the credibility of the IPCC, which has been considered an authoritative source for information about climate change because of its policy of carefully reviewing and analyzing hundreds and even thousands of published, peer-reviewed scientific studies. But the scientists who uncovered the error say that the mistake, and the reliance on news reports and unpublished studies, is rare. "I don't think it ought to affect the credibility of the edifice as a whole," says J. Graham Cogley, professor of geography at Trent University, who was key to identifying the original sources of the information in the IPCC report.

The error has been traced to the fact that the IPCC permits the citation of non-peer-reviewed sources, called "grey literature," in cases where peer-reviewed data is not available. It requires that these sources be carefully scrutinized, but that didn't happen in this case. The process has "gone spectacularly wrong in this particular instance," Cogley says.

That claim went unchallenged during the normal, multistep review process used by the IPCC. The error wasn't widely noticed until last November, when a group of scientists began discussing a new study of the Himalayan glaciers. The discussion led Cogley to look up the original sources for the claims in the IPCC report. He found two sources, a news report in the London-based magazine New Scientist about an as-yet unpublished study, and an article that estimated the glaciers could shrink to one-fifth their current area by 2350, rather than 2035, putting the IPCC report off by about 300 years. His finding is described in a letter to the editor to be published January 29 in the journal Science. Field confirms that the New Scientist was one of the sources, but not the report giving the date of 2350.

David Victor, the director of the Laboratory on International Law and Regulation at the University of California, San Diego, says that the error should not lead to a major change in the IPCC's process. "A very small fraction of IPCC reports stems from grey literature," and an outright ban on such sources would be a bad idea, since it would prevent the organization from drawing on certain types of valuable information. For example, government reports, or even raw data on greenhouse gas levels or measurements of the extent of glaciers, are often not a part of peer-reviewed literature.

Cogley recommends two main changes. First, all sources cited should be readily available to reviewers, which would have made it easier to see that the source for the 2035 date was a news report. (The IPCC report does not cite the New Scientist, but rather another document, which in turn cited the New Scientist.) Second, he says, researchers working on different parts of the IPCC report should work together more closely. Kaser says that if during the normal review process even one glaciologist of the many who worked on the Working Group I report ("The Physical Science Basis") would have carefully read the Working Group II report, the error would have been caught.

(The claim that the Himalayan glaciers could disappear within 25 years was included in the recent Technology Review feature "The Geoengineering Gambit." A correction can be found here.)

By Kevin Bullis

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Cosmic Ray Decreases Affect Atmospheric Aerosols And Clouds

ScienceDaily (Oct. 6, 2009) — Billions of tonnes of water droplets vanish from the atmosphere in events that reveal in detail how the Sun and the stars control our everyday clouds. Researchers of the National Space Institute in the Technical University of Denmark (DTU) have traced the consequences of eruptions on the Sun that screen the Earth from some of the cosmic rays -- the energetic particles raining down on our planet from exploded stars.

"The Sun makes fantastic natural experiments that allow us to test our ideas about its effects on the climate," says Prof. Henrik Svensmark, lead author of a report newly published in Geophysical Research Letters. When solar explosions interfere with the cosmic rays there is a temporary shortage of small aerosols, chemical specks in the air that normally grow until water vapour can condense on them, so seeding the liquid water droplets of low-level clouds. Because of the shortage, clouds over the ocean can lose as much as 7 per cent of their liquid water within seven or eight days of the cosmic-ray minimum.

"A link between the Sun, cosmic rays, aerosols, and liquid-water clouds appears to exist on a global scale," the report concludes. This research, to which Torsten Bondo and Jacob Svensmark contributed, validates 13 years of discoveries that point to a key role for cosmic rays in climate change. In particular, it connects observable variations in the world's cloudiness to laboratory experiments in Copenhagen showing how cosmic rays help to make the all-important aerosols.

Researchers have traced the consequences of eruptions on the Sun that screen the Earth from some of the cosmic rays.

Other investigators have reported difficulty in finding significant effects of the solar eruptions on clouds, and Henrik Svensmark understands their problem. "It's like trying to see tigers hidden in the jungle, because clouds change a lot from day to day whatever the cosmic rays are doing," he says. The first task for a successful hunt was to work out when "tigers" were most likely to show themselves, by identifying the most promising instances of sudden drops in the count of cosmic rays, called Forbush decreases. Previous research in Copenhagen predicted that the effects should be most notice-able in the lowest 3000 metres of the atmosphere. The team identified 26 Forbush decreases since 1987 that caused the biggest reductions in cosmic rays at low altitudes, and set about looking for the consequences.

Forgetting to sow the seeds

The first global impact of the shortage of cosmic rays is a subtle change in the colour of sunlight, as seen by ground stations of the aerosol robotic network AERONET. By analysing its records during and after the reductions in cosmic rays, the DTU team found that violet light from the Sun looked brighter than usual. A shortage of small aerosols, which normally scatter violet light as it passes through the air, was the most likely reason. The colour change was greatest about five days after the minimum counts of cosmic rays.

Why the delay? Henrik Svensmark and his team were not surprised by it, because the immediate ac-tion of cosmic rays, seen in laboratory experiments, creates micro-clusters of sulphuric acid and water molecules that are too small to affect the AERONET observations. Only when they have spent a few days growing in size should they begin to show up, or else be noticeable by their absence. The evidence from the aftermath of the Forbush decreases, as scrutinized by the Danish team, gives aerosol experts valuable information about the formation and fate of small aerosols in the Earth's atmosphere.

Although capable of affecting sunlight after five days, the growing aerosols would not yet be large enough to collect water droplets. The full impact on clouds only becomes evident two or three days later. It takes the form of a loss of low-altitude clouds, because of the earlier loss of small aerosols that would normally have grown into "cloud condensation nuclei" capable of seeding the clouds. "Then it's like noticing bare patches in a field, where a farmer forgot to sow the seeds," Svensmark explains. "Three independent sets of satellite observations all tell a similar story of clouds disappearing, about a week after the minimum of cosmic rays."

Huge effects on cloudiness

Averaging satellite data on the liquid-water content of clouds over the oceans, for the five strongest Forbush decreases from 2001 to 2005, the DTU team found a 7 per cent decrease, as mentioned earlier. That translates into 3 billion tonnes of liquid water vanishing from the sky. The water remains the-re in vapour form, but unlike cloud droplets it does not get in the way of sunlight trying to warm the ocean. After the same five Forbush decreases, satellites measuring the extent of liquid-water clouds revealed an average reduction of 4 per cent. Other satellites showed a similar 5 per cent reduction in clouds below 3200 metres over the ocean.

"The effect of the solar explosions on the Earth's cloudiness is huge," Henrik Svensmark comments. "A loss of clouds of 4 or 5 per cent may not sound very much, but it briefly increases the sunlight rea-ching the oceans by about 2 watt per square metre, and that's equivalent to all the global warming dur-ing the 20th Century."

The Forbush decreases are too short-lived to have a lasting effect on the climate, but they dramatize the mechanism that works more patiently during the 11-year solar cycle. When the Sun becomes more active, the decline in low-altitude cosmic radiation is greater than that seen in most Forbush events, and the loss of low cloud cover persists for long enough to warm the world. That explains, according to the DTU team, the alternations of warming and cooling seen in the lower atmosphere and in the oceans during solar cycles.

The director of the Danish National Space Institute, DTU, Eigil Friis-Christensen, was co-author with Svensmark of an early report on the effect of cosmic rays on cloud cover, back in 1996. Commenting on the latest paper he says, "The evidence has piled up, first for the link between cosmic rays and low-level clouds and then, by experiment and observation, for the mechanism involving aerosols. All these consistent scientific results illustrate that the current climate models used to predict future climate are lacking important parts of the physics".

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