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Worst case scenario: How bad could a tropical cyclone be?

Before Natalie Portman slipped on a pair of ballet shoes and won an Academy Award, the term “black swan” was already full of psychological tension. Nassim Taleb coined the term to describe extreme, unforeseeable events with nasty consequences, whether in the natural world or in financial markets.

A notch down from there, we find what can be described as “gray swans”—things that are stronger than anything we’ve seen, but that we can foresee to be physically possible. Given that we have pretty short historical records in most places, it’s not much of a stretch to accept that we haven’t experienced the full range of possible weather. And after all, low probability events happen eventually.

Recently Princeton’s Ning Lin and MIT’s Kerry Emanuel went gray swan hunting in the world of tropical cyclones, using climate models to simulate many more storms than exist in our brief historical records. And some of the gray swans they found look like mean bastards.

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Would warming stop after greenhouse gas emissions end? Not quite

The latest IPCC report estimated our remaining “carbon budget” that would give us a chance of reaching the goal of keeping global warming below 2 degrees Celsius this century. That estimate was created using a simpler class of climate model that can crank out long or repeated simulations without tying up a supercomputer for a week. A new study using one of the most complex models, however, suggests that the simpler models get a key issue wrong: they overestimate how much carbon we can emit if we actually want to stay below 2 degrees Celsius over the centuries that follow.

A recent study used one of those simpler models (technically known as “Earth System Models of Intermediate Complexity," or EMICs) to look at how long it takes us to reap the benefits of cutting emissions. Rather than the oft-repeated estimate that there is a delay of about 40 years, the researchers found that the peak in temperature came just 10 years after emitting a simulated pulse of CO2. However, they only modeled about a hundred years.

ETH Zürich’s Thomas Frölicher and David Paynter of NOAA’s Geophysical Fluid Dynamics Laboratory turned to a more complex model and a much longer timeframe to investigate a related question: what happens long after we stop emitting greenhouse gases?

Using their model, they simulated a scenario in which CO2 emissions grew 1 percent each year for 100 years, raising the atmospheric concentration from 286 to 745 parts per million, and raising temperature by 2 degrees Celsius. At that point, CO2 emissions dropped to zero. Then, they simulated nine more centuries, watching atmospheric CO2 drop back to 476 parts per million as it gradually moved into the ocean and natural reservoirs on land.

Rather than tie up a supercomputer with an even longer simulation, they estimated the temperature after another 9,000 years using measures of the model’s characteristics and lower-resolution simulations of atmospheric CO2 changes.

In addition, they pooled simulations of 12 similarly complex models to estimate comparable results for the same scenario. On the flip side, estimates for eight of those simpler EMIC models were also put together.

Surprisingly, the two types of models diverged significantly over the first hundred years after emissions ceased. While the simpler models hit their peak temperature at the end of the first century, cooling about 0.6 degrees Celsius by the end of the first thousand years, the more complex models kept warming. The researchers’ model warmed an additional 0.5 degrees Celsius between year 100 and year 1,000. On average, the other more complex models warmed an additional 0.2 degrees Celsius.

At the end of 10,000 years, the more complex models averaged just 0.1 degree Celsius below their temperature in year 100, while the simpler models had dropped around 0.8 degrees Celsius.

Because the IPCC’s “carbon budget” estimates were based on these simpler models, this has an interesting implication. If you want to stay below 2 degrees Celsius warming—not just this century, but in the centuries to come—you may need to keep to a stricter budget. You’d have to cut that budget by as much as 20 percent, in fact. Otherwise you may limit global warming to less than 2 degrees Celsius this century only to find that temperature still ticks slowly upward over the next few hundred years. That would leave future generations with the task of artificially pulling CO2 out of the atmosphere in order to truly stabilize their climate.

Why is it that the two types of models simulate slightly different futures? The researchers have a guess. While all the models involved sit within the usual range of “equilibrium climate sensitivity”—the amount of eventual warming for an increase of CO2 that is then held constant—the simpler EMIC models seem to get to their equilibrium faster.

The researchers think the difference comes down to the simulation of high-latitude oceans. Because there is much more mixing of shallow and deep water there, these regions of the ocean warm more slowly than water near the equator. But when these regions do warm, they have a larger impact on global temperature because of the way the feedbacks play out.

In the more complex models, it’s this gradual uptake of heat by high-latitude oceans that lifts global temperature over the centuries following the end of CO2 emissions—this warming influence ends up stronger than the cooling influence of falling CO2 concentrations.

In the simpler EMIC models, that isn’t true. Thomas Frölicher told Ars that he thinks that could be due to the models’ simpler cloud simulation, since clouds are an important part of the regional feedback to ocean warming.

That said, there are a number of things that remain to be nailed down here. But overall, this is another reminder that less is most definitely better when it comes to the amount of greenhouse gases we add to the atmosphere.

Open Access at Environmental Research Letters, 2015. DOI: 10.1088/1748-9326/10/7/075002  (About DOIs).

Yes, climate change has a hand in the California drought

The California drought may have put water in short supply, but debate about it is in surplus. Water use has come under even greater scrutiny as Californians struggle to deal with the current and future reality. Groundwater overuse during the drought has reached epic proportions, with the land surface in some locations sinking almost two inches per month as a result. In addition to arguing over how to use the little water they have, people are also debating the question of whether humans are partly to blame not just for water supply issues, but for the drought itself.

Late last year, a NOAA report concluded that climate change wasn’t required to explain the lack of rainfall, while a separate tree ring study found that the drought looked to be the most severe in 1,200 years. The rains have been fended off by a persistent pattern of high air pressure above the northeastern Pacific that seems to have been a product of ocean surface temperature patterns farther west.

But rainfall isn’t the only factor that contributes to drought. The heat of the day sucks moisture out of the soil, helped along by blowing winds. Boost either of those factors, and you’ll need more rainfall to keep the drought account from going in the red. Since the globe is warmer now than it was a century ago and California is part of that globe, it’s fair to guess that climate change isn’t helping.

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China emitted a little less greenhouse gas than we thought

As a rapidly emerging economy with over four times the population of the US, China is playing an increasingly large role in the story of climate change. That makes trends in energy production there rather important. Unfortunately, Chinese emissions data aren’t the best, leaving significant error bars and discrepancies between different estimates.

A new study led by Zhu Liu went back over data covering 2000 to 2013 to pull together something a little more reliable. The study concludes that China emitted less greenhouse gas than we thought.

Instead of relying on iffy energy consumption data, the researchers went back to the production of coal, oil, and gas in China, and to imports and exports. They came up with a number that was actually a little higher than the Chinese government’s national estimate.

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Some permafrost might soak up methane as climate warms

Talk of a warming planet often focuses on places that are cold. Glaciers shrink and raise sea level. Arctic sea ice dwindles, opening an actual northwest passage in the summer. And permafrost thaws, pulling vast amounts of organic matter out of the freezer to spoil and add to the greenhouse gases in the atmosphere. Lots of research has focused on organic-rich permafrost and the amount of carbon dioxide and methane it could produce as microbes break down all that food.

But that’s only a slice of the world’s permafrost area. The rest is more like frozen dirt than frozen peat, with a much lower carbon content. A team of researchers led by Princeton’s Chui Yim Lau and Brandon Stackhouse traveled to Axel Heiberg Island in the Canadian Arctic to see what kind of microbes they could find in the carbon-poor permafrost, and to find out how they might respond to warmer temperatures.

The researchers periodically placed special sampling chambers down on the ground and measured the changes in methane inside over a few minutes or hours. If microbes were busy producing methane, it would accumulate inside the chamber at some rate. In this case, however, methane inside the chamber decreased—a phenomenon attributed to methane-munching bacteria that have occasionally been observed at other permafrost study sites.

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A successful strategy to get college students thinking critically

“We aren’t teaching students how to think critically!” So goes the exasperated lament you have probably heard and possibly uttered. The thing is, that’s a crazy hard thing to do. It may seem like a logic class should teach you to think in a more disciplined way, for example, but the sad fact is that those mental habits are very unlikely to transfer beyond the walls of the logic course. There are many different styles and contexts of critical thinking, and there is no magic subroutine that we could insert into our mental programming that covers them all.

But despair is not the only option. Effective coursework can build important and useful critical thinking skills. Doug Bonn at the University of British Columbia and Stanford’s N.G. Holmes and Carl Wieman focused on good scientific, quantitative thinking when teaching a group of first-year physics students. And like good critically thinking educators, they put their strategy to the test and published the results so they can be evaluated by others.

In this freshman calculus-based physics course, students worked through weekly experiments in lab sections as most physics students do. But the researchers tried a little something different a couple years ago when a fresh class of 130 students came in. In their early lab sections, the students were guided through comparisons between multiple experimental datasets and between experimental datasets and mathematical models.

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Lager-brewing yeast was probably born twice

Guinness stout and Bud Lite differ in, to be conservative, several ways, but one is that they’re brewed with very different types of yeast. Lager isn’t just a beer style, it’s a yeast lifestyle. Humans have been brewing with ale yeast—Saccharomyces cerevisiae—for thousands of years. But it was less than 600 years ago that European brewers stumbled on lager yeast, which behaves very differently and produces that distinctive lager flavor.

Lager yeast is a cross of ale yeast with another species, but it took until 2011 for that other species to finally be identified in Patagonian forests. A new study led by University of Wisconsin-Madison researchers EmilyClare Baker and Bing Wang presents the genome of this recently discovered parent, Saccharomyces eubayanus.

By comparing the genome with the two strains of lager yeast around today, the researchers may have settled a dispute about the biological origins of lager yeast. Looking at the two strains, there are many more differences between the ale yeast portions of their genomes than have accumulated in the Saccharomyces eubayanus portions. This points to independent hybridization events starting with different ale yeast parents rather than a single hybrid that has since split into two strains.

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Imports from China are blocking US ozone improvements

For a simple molecule, ozone (O3) wears many hats. Up in the stratosphere, the ozone layer provides planetary sunscreen, absorbing UV radiation before it can reach the Earth. Between the surface and the stratosphere, ozone’s significance comes from absorbing infrared radiation from the Earth—it’s a greenhouse gas. And down at ground level, ozone's reactivity makes it a harmful enough lung irritant that it’s a part of the daily weather report in some cities.

Ozone is produced in the atmosphere naturally, but it’s also created as a result of air pollution. In particular, nitrogen oxides react with sunlight to let rogue oxygen atoms loose, which can get together with friendly O2 molecules in the lower atmosphere, forming O3. By cutting the emissions of those “ozone precursors,” we can dial back the amount of ozone down here where we breathe. In the western US, emissions of nitrogen oxides were reduced by 21 percent between 2005 and 2010, yet ozone stayed about constant. Part of the answer to that conundrum lies across the Pacific, according to a new study led by Wageningen University’s Willem Verstraeten.

The suggestion that ozone from China is ending up in the US isn’t new, but the researchers turned to data from NASA’s Aura satellite (launched in 2004) to improve past estimates. The satellite data confirmed that nitrogen oxides had declined across the American West, while average ozone hadn’t changed much (some areas saw a slight decrease and some a slight increase). In China, on the other hand, emissions of nitrogen oxides rose about 21 percent between 2005 and 2010, and ozone increased by around seven percent.

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Piecing together April’s deadly earthquake in Nepal

Seismic risks can loom over a region for long periods of time before striking. In April, longstanding fears about Kathmandu’s susceptibility to earthquakes were realized when the shaking of a magnitude 7.8 Himalayan quake killed more than 8,000 people. A pair of new studies published this week piece together what happened along the fault that moved, and they tell us where the risk is highest for the next big earthquake in the area.

The mighty Himalayas have been driven up into the sky by the collision of Eurasia and India, which has migrated north like a tectonic rocket over the last 100 million years. The Indian plate is being crammed beneath the crumpled Himalayan rocks along a dangerous fault that ramps downward to the north.

Lots of GPS sensors and seismometers have been deployed in the area to help seismologists study earthquakes here. Combined with precise satellite measurements of surface elevation changes, researchers have the means to work out where the movement on the fault must have occurred.

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Tracking Earth’s changing magnetic field using South African hut fires

One “fun fact” that emerges from geology is that the magnetic north pole hasn’t always been near the geographic North Pole—it also keeps a home near the geographic South Pole, which it occupies when the orientation of Earth's magnetic field flips. Although magnetic flips appear more or less randomly distributed through time, it’s tempting to think we’re overdue for a flip, given how long it has been since the last one (about 780,000 years). Add in observations showing that the north pole has been wandering pretty rapidly as of late and that the overall strength of the field has been declining, and you might even get your hopes up.

The weakening of the field has been mainly down to action in the Southern Hemisphere. There’s a long-lived region of lower field intensity stretching from southern Africa to South America that has been getting even weaker. Models of the Earth’s magnetic field are a little fuzzy there because we don’t have many records of past behavior from that area. That makes it hard to know what to make of its current behavior.

John Tarduno of the University of Rochester and the University of KwaZulu-Natal led a team of researchers looking to fill in some of the historical gaps by building a record from southern Africa. They relied not on a geologic record, but on unintentional archives left behind by human communities. Centuries ago, the villages of people who farmed the area responded to droughts with ritual burnings of huts, grain bins, and animal enclosures. As the structures burned, the intense heat would essentially fire the clay floors like ceramic pottery (and in the case of the animal enclosures, bubbly glass). While still hot, magnetic minerals could align with the Earth’s magnetic field, only to be frozen in place as the material solidified. So each burned structure created a magnetic snapshot.

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