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Models challenge temperature reconstruction of last 12,000 years

Ilulissat, Greenland in the summer.

Climate records, like tree rings or ice cores, are invaluable archives of past climate, but they each reflect their local conditions. If you really want a global average for some time period, you’re going to have to combine many reliable records from around the world and do your math very carefully.

That’s what a group of researchers aimed to do when (as Ars covered) they used 73 records to calculate a global overview of the last 11,000 years—the warm period after the last ice age that's called the Holocene. The Holocene temperature reconstruction showed a peak about 7,000 years ago, after which the planet slowly cooled off by a little over 0.5 degrees Celsius until that trend abruptly reversed over the last 150 years. That behavior mirrored the change in Northern Hemisphere summer sunlight driven by cycles in Earth’s orbit.

A new study published in the Proceedings of the National Academy of Sciences and led by the University of Wisconsin’s Zhengyu Liu delves into a problem with that pattern—and it’s not what climate models say should have happened.

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Magnitude 8.2 earthquake off Chile increased risk nearby

Damage following the tsunami from the April 2014 earthquake.
Juan González-Carrasco (Universidad Catolica del Norte, Chile)

Sometimes it seems like the Internet holds as many ridiculous claims about predicting earthquakes as it does cat memes. While it’s very clear that neither seismologists nor anyone else can fully predict earthquakes, that doesn’t mean the scientists know nothing.

The basic process behind an earthquake is pretty simple. Friction between two blocks of rock trying to slide past each other along a fault holds them in place until the sliding force is too great, and then BOOM!—an earthquake. We can measure that sliding very precisely, so as the strain on the fault mounts, we know an earthquake will happen; it’s just a question of when. And the greater the strain that has accumulated since the last earthquake, the larger the potential magnitude of the next one.

Along a long subduction zone, where an oceanic plate slides beneath a continental plate, faults slip one section at a time. Sections that haven’t slipped in a while but sit between sites of recent major earthquakes are known as “seismic gaps.” Those sections are likely to host the next major earthquake in the region.

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Three massive volcanic eruptions light up Jupiter’s moon Io

Images from August 15 at three different wavelengths, and one image from August 29 showing the third eruption.

Jupiter’s moon Io is the most volcanically active body in our solar system, so it’s not a shock that astronomers captured several eruptions while their telescopes were trained on the satellite. However, the three eruptions were uncommonly massive (among the 10 largest seen there) and occurred within the span of a couple of weeks—eruptions of this class are only thought to occur every other year, on average. Researchers may be able to glean enough from these images to help us get to the bottom of a couple of Ionian mysteries.

Io’s prodigious volcanic output is the result of tidal heating—gravitational squeezing as a result of its slightly oblong orbit around Jupiter, along with some tugs by fellow Jovian moons. Though Io is roughly the same size as Earth’s own Moon, the flow of heat from its core toward its surface is roughly 30 times greater than that of Earth. As a result, there’s usually at least one active volcano whenever astronomers observe Io. In fact, a huge lava lake some 200 kilometers across, called Loki Patera, is usually visible to infrared telescopes. On thirteen occasions between 1978 and 2006, unusually large eruptions called outbursts were observed. Three more have now been added to that number.

Jupiter’s magnetic field holds a curious torus (or ring donut if you’re hungry) of plasma believed to originate from Io’s volcanism. A new Japanese space telescope, launched in September, had been scheduled to spend some time studying that plasma torus, and so several ground-based telescopes had begun monitoring Io’s volcanic activity in August. On August 15, a telescope at the Keck Observatory in Hawaii recorded two bright infrared spots in the far south of Io, which hasn’t been known for this kind of activity.

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Strong La Niñas recently? Blame the Atlantic—and a volcano

Chaos theory is sometimes described with an exaggerated story about the flapping of a butterfly’s wings affecting the formation of a hurricane thousands of miles away. Some “butterflies” flap harder than others, of course—a volcanic eruption can be one hell of a butterfly. According to a new study, the 1991 eruption of Mt. Pinatubo, which made a dent in the average global temperature for a couple of years, may also have a lot to do with the slower surface warming more than a decade after its eruption.

Research has made it clear that a string of La Niñas—where cold water rises to the surface in the eastern tropical Pacific—has pulled down average global temperatures in recent years. The oscillation between La Niña and El Niño conditions is a major factor in the year-to-year variability of average global surface temperatures.

So why has the coin flip come up “La Niña” so frequently lately? It appears that stronger trade winds over the Pacific—which blow westward, pushing warm surface water in the tropical Pacific as they go and bringing up the cold waters of the La Niña—are responsible. And so, you should be asking, why have the trades strengthened?

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Among meats, beef has a beefy environmental footprint

When people talk about reducing their “carbon footprint,” transportation and energy use in the home usually get all the attention. Diet deserves to be a part of that conversation, too, however. The global agricultural system is complex, and not all food choices are created equal in terms of their impact on climate and their use of resources.

Agriculture accounts for roughly 12 percent of human-caused greenhouse gas emissions. Population growth obviously increases the demand for agricultural production, but there’s another important trend as well—the rising consumption of meat. People in many developing nations are eating more meat as they gain the means to afford it. This is significant, as meat is a sort of demand multiplier because of the crops needed to feed livestock. A field of corn, for example, may be able to feed x number of people, but it can feed far fewer if it’s used to raise cattle.

The animal part of our diet is a significant portion of the agricultural system. Animal feed requires the output of 40 percent of US cropland—and if you include pastureland for grazing, it accounts for 40 percent of all US land. Feed also uses 27 percent of total irrigation and half of the nitrogen fertilizer used, and it contributes about five percent of total greenhouse gas emissions in the US.

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Are the people who refuse to accept climate change ill-informed?

Polls relating to publicly controversial scientific issues often trigger a great wailing and gnashing of teeth from science advocates. When large proportions of a population seem poorly informed about evolution, climate change, or genetically-modified foods, the usual response is to bemoan the state of science literacy. It can seem obvious that many people don’t understand the science of evolution, for example—or the scientific method, generally—and that opinions would change if only we could educate them.

Research has shown, unfortunately, it's not that simple. Ars has previously covered Yale Professor Dan Kahan’s research into what he calls “cultural cognition,” and the idea goes like this: public opinion on these topics is fundamentally tied to cultural identities rather than assessment of scientific evidence. In other words, rather than evaluate the science, people form opinions based on what they think people with a similar background believe.

That shouldn’t come as a shock, especially given the well-known political or religious divides apparent for climate change and evolution.

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A simple explanation for awe-inspiring sandstone arches

Delicate Arch at Arches National Park in Utah.

There’s no need to ask what the appeal of Arches National Park is—it’s in the name. The gorgeous sandstone arches there seem almost impossible. How and why should the relentlessly erosive wind carve such a fantastic structure? The arches seem too vulnerable, too artificial.

And arches aren’t the only trick that sandstone has up its sleeve. Bizarre, mushroom-shaped pillars seem even more absurd, as if they were carefully placed by an incredibly patient and even more incredibly strong Zen garden enthusiast. In some places, networks of sandstone pillars even hold up ledges like a miniature Moria.

We know plenty about how this erosion takes place, and some details about why some sections of the rock erode faster than others, but the primary cause of these shapes has eluded geologists. A new study led by Jiri Bruthans of Charles University in Prague has revealed a surprisingly simple explanation.

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Detailed imaging of Mount Rainier shows subduction zone in glorious detail

A cross section of Washington's Cascade Range from west to east (left to right) passing near Mt. Rainier, indicated by a red triangle. The colors represent electrical resistivity, with red being low. Contour lines show temperature in degrees Celsius. Small red circles show the centers of earthquakes.

Most people know that the Pacific Ring of Fire is related to boundaries between tectonic plates, but there’s a common misconception about where the magma comes from to fuel those volcanoes. At those boundaries, called subduction zones, a plate made of denser oceanic crust dives beneath a continent (or another oceanic plate). It’s not that the diving plate heats up and melts as it sinks downward, though.

Actually, the minerals in the diving plate contain lots of water, and that water migrates upward as the plate slowly warms up. The addition of water to hot mantle rocks lowers the melting point of the rock, and this effect is enough to convert some mantle rock into magma. Since magma is less dense than solid rock, it works its way upward toward the surface, resulting in the arcs of volcanoes we see along subduction zones.

Within this simplified picture, however, there are complexities and open questions. Does the water simply rise directly into the mantle rocks above, or does it take a more tortuous path? Is that water the cause of all the magma production in an area, or does some magma form because the flow of mantle rock brings some up to lower pressures where it can melt?

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Gravity satellites could provide warning months ahead of floods

Flooding along the Missouri River on the Iowa-Nebraska border in 2011.

When the twin GRACE satellites were launched in 2002, the casual observer might have been underwhelmed by their mission—to make precise measurements of Earth’s gravity. They’ve proved, however, to be unbelievably useful Swiss Army knives of geoscience, measuring everything from the loss of ice from Greenland and Antarctica to groundwater depletion in California. Now, the GRACE that keeps on giving has been shown to improve warnings ahead of major floods in some areas.

For many, floods seem to show up suddenly and then overstay their welcome. In some situations, they can be incredibly damaging and often quite dangerous. But a lot more goes into determining the size of a flood than just the amount of rain that falls, and that data provides the key to better forecasting of flood risk.

When looking at graphs of streamflow—the volume of water traveling downstream per second—for a river or stream, hydrologists can identify two kinds of behavior. There’s the consistent base flow, supplied mainly by groundwater entering the river, and the temporarily higher flow that follows rain storms.

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Greenland melt may have pushed sea level six meters higher in the past

The edge of the Greenland ice sheet near Kangerlussuaq, with exposed bedrock in the foreground.
Alberto Reyes

Earth’s climate system will respond to the stronger greenhouse effect we’ve produced in various ways. But one key question about its response is how much ice will be lost from the great ice sheets of Greenland and Antarctica. Push them too far outside their climatic comfort zone, we know, and a large retreat of glacial ice can follow, raising global sea levels.

Given that the innards of these ice sheets are complicated and inaccessible, researchers rely heavily on what we can discover about their pasts. One key point in the past has been the warm interglacial period around 400,000 years ago. The cycles in Earth’s orbit that govern the timing of the ice ages conspired to produce an exceptionally long respite from the cold at this time—twice as long or more than the most recent interglacial period about 120,000 years ago. It may have been warmer, as well, and some estimates put sea level in the vicinity of six to 13 meters higher than it is today.

Did that sea level rise come mostly from a smaller Greenland ice sheet, loss of ice from Antarctica, or some mixture of the two? We don’t know, and it’s difficult to answer since glaciers destroy the evidence of their past retreat when they expand again. A new study led by Alberto Reyes (now at the University of Alberta) and Oregon State’s Anders Carlson sifted sediments off Greenland’s coast to find clues about what the ice sheet was up to at that time.

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