The seas’ most sought-after fish are swimming between a rock and a hard place: the fisherman’s net and an encroaching mass of suffocating water.

A recent study has uncovered a new dose of bad news for ocean fish and the fishing industry. Areas of the deep ocean with little dissolved oxygen, called dead zones, are expanding and, thus, shrinking many fishes’ watery homes.

One driving force behind the predicament is none other than that pesky climate problem.

“Climate change is actually working in tandem with overexploitation of the animals to push these populations into a real dangerous place in terms of population collapse,” said Eric Prince, a fisheries biologist with the National Oceanic and Atmospheric Administration’s Southeast Fisheries Science Center and co-author of the study.

For example, Prince and his colleagues calculated that the Atlantic blue marlin, an economically valuable fish that was a focus of their study, has lost about 15 percent of its habitat from expanding dead zones since 1960. Dwindling habitat threatens not only the lives of fishes, but also the sustainability of the already ailing fishing industry.

Breathing room

Like their above-water brethren, fish need oxygen, which is dissolved in the water. Big, predatory fish, such as the blue marlin, need more dissolved oxygen than most, because they require lots of energy to grow and survive. Without sufficient oxygen, they’ll suffocate.

The level of oxygen in the water thus partly delineates fish habitat boundaries. Dead zones often draw these borders.

As climate change causes open ocean dead zones to balloon, fish habitat deflates.

Diagram modified from one originally published in Deep Sea Research Part I: Oceanographic Research Papers, Vol 57, Issue 4, Lothar Stramma, Sunke Schmidtko, Lisa A. Levin, & Gregory C. Johnson. Ocean oxygen minima expansions and their biological impacts, 587-595, Copyright Elsevier (2010).

Technically known as oxygen minimum zones, dead zones are actually a natural occurrence. Found at depths of between 200 and 1000 meters, they are caused partly by seawater circulation and partly by the decomposition of organic matter, namely deceased sea critters that sink from surface waters.

As aerobic bacteria nosh on the organic matter, they use up the oxygen in the water. Eventually, hypoxia happens—the water becomes so depleted of oxygen that many creatures can’t survive.

Since deep-sea dead zones are insulated from the ocean’s surface, where the water borrows oxygen from the atmosphere, they can only reload with oxygen if currents make a long-distance delivery, according to Sunke Schmidtko, an oceanographer at the University of East Anglia, the other co-author of the study.

Deep-sea dead zones are different from their coastal cousins like the one in the Gulf of Mexico. Coastal dead zones form due to a buildup of agricultural fertilizer that rivers, such as the Mississippi, collect and then flush out to sea, causing abnormal blooms of plant life.

De-fizzing the ocean

But climate change is turning what Mother Nature does normally into a big problem. As the air is getting hotter, so is the water, and warmer water can hold less oxygen than colder water.

This is similar to what happens to a soft drink on a hot day. After sitting in the heat and sun, the fizz fizzles, and you are left with a flat, carbon dioxide-depleted beverage.

Also, warmer surface waters are less likely to sink to the ocean’s lower layers, because warm water is lighter than the colder water below, Schmidtko explained. In other words, as the oxygen-rich surface layers heat up, they could have a harder time delivering oxygen to the deeper ocean.

Schmidtko clarified that oceanographers are still trying to determine how exactly climate change is affecting the ocean, but with their knowledge of how water works, these represent their current speculations.

The rock below

With less oxygen to go around, oxygen minimum zones are swelling and intruding on many fishes’ living zones.

For example, marlins often dive deep to feed, sometimes as far down as 800 meters. However, in the eastern Atlantic’s growing dead zone, which is already one of the largest in the world, Prince found that marlins can’t dive as deep as their west-side counterparts.

“They need to go where the food is and where they can breathe,” he said.

With less breathing room below, the floor of their habitat rises, and they are pinned to the surface layers. With nowhere to go but up, marlins become squished into tighter, testier quarters with other predatory fish and their prey. They also find it harder to dodge a waiting fishing hook or net.

“Concentrating them makes it much easier for overexploitation by [humans],” said Prince.

The increasing concentration of animals at the top could also lead to a boost in the amount of sinking organic matter, which would further worsen the oxygen shortage below.

Softening the hard place above

As a prized catch, Atlantic blue marlins are already victims of overharvesting. In fact, their populations have dropped 60-64 percent over the past three fish generations (14-18 years).

But the growing dead zones can actually fool scientists and fishermen into thinking fish populations are doing just fine, since more fish are squeezed into a smaller area. Thus, to ensure the dead zone-fishing vise does not become their demise, Prince said scientists must more carefully monitor fish populations, as well as the expansion of the dead zones.

While fish stock assessments are starting to incorporate this information, Prince warned the pace needs to quicken.

And if the Earth is to continue warming, as most scientists predict, Schmidtko added that humans should chill out on fishing.

After all, we will never be capable of “ventilating the ocean,” he said.

Seven viewpoints

Introduction

Katharine Hayhoe

Richard Alley

John Nielsen-Gammon

John Williams

Michael Notaro

Kent McGregor

Kevin Trenberth

Drought and searing heat in Texas: Is this the face of global warming?

Courtesy Eric Bruning, Texas Tech University Atmospheric Science

The cold front that blew through Lubbock, Texas on Oct. 17 raised a dust storm not seen since the 1930s Dust Bowl. The dust storm, seen in this movie, is called a “haboob,” an event more common to Saudi Arabia than Texas.

On Oct. 17, a cold front blowing through Lubbock, Tex. raised a red dust cloud that recalled the awesome Dust Bowl of the 1930s, an epoch of drought, enormous dust storms, poverty and social upheaval that depopulated the Great Plains.

The 2011 dust storm served as an exclamation point on a cruel Texan summer, with drought, wildfires, and temperature records that would not quit. On Oct. 19, the Lower Colorado River Authority, source of much water in the Southwest, warned customers that the drought was likely to force another 20 percent cut in water supplies.

On Oct. 18, Texas Lt. Gov. David Dewhurst instructed the state legislature to study drought-related problems like helping homeowners protect against fire, and ensuring that utilities would get enough water to cool their generators.

As far as we could tell, the multi-pronged assignment did not mention something that many observers think contributes to heat waves, fires and droughts: climate change.

Many recent “natural” disasters have raised the same question: Is the no-sense-denying-it-any-longer human-caused planetary warming intensifying devastating hurricanes, giant rainfalls and snowfalls, or the deadly heat waves in Europe (2003) or Russia (2010)?

Despite political skepticism in the United States, the scientific study of changing climates has grown exponentially for 20 years. In 2009, almost 14,000 research reports focused on climate change, and 20 scientific journals are devoted to the issue.

UPDATED NOV. 18: Today, the New York Times reported that a United Nations panel has concluded that “At least some of the weather extremes being seen around the world are consequences of human-induced climate change and can be expected to worsen in coming decades. It is likely that greenhouse gas emissions related to human activity have already led to more record-high temperatures and fewer record lows, as well as to greater coastal flooding and possibly to more extremes of precipitation, the report said.”

Enough introductory blather. Let’s ask some experts: Is the hot, dry weather in Texas a reflection of global warming? Or is it just proof that the essence of weather is its natural variability? The Why Files talked to seven climate scientists. Peruse their viewpoints in the box above.

El Niños, the global cycles of weather that are driven by a hot spot in the tropical Pacific Ocean, have been linked to drought, storms and famine in many parts of the tropics.

Today, a study in Nature finds that deadly conflicts have started twice as often during the el Niño years – but only in the many countries affected by el Niño.

Scientific interest in el Niño mushroomed during the 1980s, when climate experts began to correlate historic cycles of anchovy harvests along the west coast of South America with changes in weather thousands of kilometers distant, and eventually unraveled a planetary cycle driven by the appearance of huge pools of warm water in the western Pacific.

Because the warming seemed to coincide with Christmas, it was called el Niño, for the Christ Child.

El Niño is now recognized as the warm-water segment of the el Niño Southern Oscillation (ENSO), which also includes a cold-water counterpart called la Nina. Now acknowledged as an engine of global climate, el Niño is linked to prolonged droughts, heat waves and crop failures.

Previous efforts to study whether weather and global warming could affect war have related past environmental changes with conflict and the decline of civilizations, says Solomon Hsiang, who completed the new study as a graduate student at the Lamont Doherty Earth Observatory at Columbia University. But the studies tended to be case-by-case, he notes, and “even if every conflict or collapse happened at random, some would occur during a period of environmental change, so this isn’t compelling evidence.”

Looking carefully

To study the issue more systematically, Hsiang and collaborators Mark Cane and Kyle Meng:

The data showed that conflicts are twice as likely to start during an el Niño, says Hsiang, and that 21 percent of overall conflicts can be attributed to el Niño. The increase was only seen in countries strongly affected by el Niño.

Surprisingly, the average changes wrought by an el Niño are quite minor, Hsiang admits – about 0.05°C rise in temperature, and about 0.1 millimeter reduction in daily rainfall.

Small is … powerful?

How could such minor changes affect warfare?

A study that correlates data does not show why they are related, but there are many ways that seemingly small effects could change human behavior, says Hsiang, who is now at Princeton University, especially considering that averages can conceal major alterations in different locations:

However, Marshall Burke, who published an influential 2009 paper ¹ that found a significant increase in warfare during hot weather in sub-Saharan Africa, noted by email that the increase in conflict was seen only inside the el Niño region, and thus, “We might conclude that these global market mechanisms are not at work.”

Still, the new study adds something to the discussion, Burke says. “The [Hsiang] paper’s main innovation is in linking historical changes in the global climate to conflict risk, whereas past studies (including ours in PNAS) looked only at the effect of local weather variations on conflict.”

Burke, a Ph.D. candidate at UC Berkeley department of agricultural and resources economics, added, “They provide very convincing evidence that ENSO-related changes in the global climate are strong drivers of conflict risk in the regions whose weather is affected by ENSO.”

Looking at limits

Mark Cane, a climate scientist at Columbia’s Lamont-Doherty Earth Observatory and a co-author of the new study, said weather does not equal destiny. “No one should take this to say that climate is our fate. Rather, this is compelling evidence that it has a measurable influence on how much people fight overall.”

Ultimately, the motivation for the new study was to peer through the keyhole of time and anticipate a warmed world, Hsiang says, but he admits that the predictive power is limited. “In relationship to global warming, we want to be careful. El Niño is very different … in terms of its spatial pattern, the changes on the ground, and the rate of change. Until we have a much better grasp of these, it’s very hard to take these results and produce any kind of projection for future climate change.”

Still, he adds, “The debate until now has been whether there is any reason to believe that a shift in climate can produce conflict.” Now, “The question is not whether it’s possible, but how much global climate will influence conflict.”

– David J. Tenenbaum

The death toll from the May 22, 2011 tornado in Joplin – now 122 — is the latest tragedy of a horrific year for tornadoes. On April 27, twisters in Alabama and nearby states killed 314, the fourth highest in U.S. history. The 480 deaths in 2011 are already the highest number since 1953, and tornado season continues through mid-August.

The Why Files asked Jonathan Martin, an expert on the large atmospheric disturbances that form tornadoes, some questions about tornado prediction. We edited the answers of Martin, a professor of atmospheric and oceanic sciences at the University of Wisconsin-Madison, after the interview.

The Why Files: What must we know to make a good tornado prediction?

The Why Files: Are predictions getting more accurate?

The Why Files: Why so much damage and death this year? Is this a result of climate change?

For decades, scientists have thought that the pre-historic Antarctic climate was governed by events at the other end of the planet — in the Arctic. That’s because variations in solar radiation in the northern summer tracked nicely with the temperature record from sediment cores and ice cores taken on or around Antarctica.

Our record of temperatures in the deep south is carried in the ratios of oxygen and hydrogen isotopes (atoms with different masses) contained in ice cores. But Thomas Laepple, of the Alfred Wegener Institute for Polar and Marine Research in Germany, has just published an article maintaining that because the Antarctic ice cores did not accumulate at a steady pace, they have not been interpreted correctly.

Today, more snow (the source of ice), gathers in winter. Because that likely also happened in the past, ice cores from Antarctic tell us more about winter than summer, says Laepple.

And God created winter!

Photo 1: Hans Oerter, Alfred Wegener Institute, Germany, Photo 2: Eric Cravens, National Ice Core Lab

This 150,000-year-old piece of Antarctic ice is 10 centimeters in diameter, and was taken from a depth of 2,250 meters. After researchers clean, measure and catalog this core, it may be stored in a giant freezer like the one in the next image (rollover).

When Laepple and his colleagues factored in this seasonal effect, the level of sunlight in the southern hemisphere suddenly began to explain Antarctic temperatures. Although the orbital cycles still globally affect solar radiation, there was no longer a need to look at the other end of the Earth to explain rhythms in Antarctic temperatures.

The orbital cycles in question are named for Serbian engineer Milutin Milankovitch, who, about a century ago, sought to understand how three slow shifts in Earth’s orbit would affect the amount of sunshine in different regions, different seasons and years.

These orbital variations, which are influenced by gravity of the moon, sun, Jupiter and Saturn, are the basis of the “Milankovitch cycle:”

As scientists examined ocean sediments and then ice cores, the Milankovitch influence on solar radiation in the Northern hemisphere became the accepted explanation for the changing global climate. But when Laepple factored in the seasonal nature of Antarctic snowfall, he found that Milankovitch could explain the climate on the southern continent more directly. “I don’t question that the Milankovitch cycle has an influence on climate,” says Laepple, “but I question that its influence on the Antarctic is coming through the Artic.”

The adjustment was needed because more ice accumulates during winter and does not affect the overall climate record, Laepple says, “but it completely changes the recording of the signal stemming from the precession of the earth axis, which was the evidence for the remote North-South connection.”

Photo 1: Steven Profaizer, Photo 2: Sepp Kipfstuhl, Alfred Wegener Institute, Germany

Scientists use massive drills to uncover the stories about past climates told in ice cores (roll over for to see a core from a depth of 2,668 meters).

How would you explain it?

Climate is never simple, notes Richard Alley, a climate expert and professor of earth science at Penn State, who was not involved in the research. The Milankovitch cycle, he says, “shifts sunshine around on the planet, with more in some places and less in others, changing the length of seasons, the total sunshine during seasons … so it is not surprising that multiple hypotheses can be advanced to explain a given climate record. Ultimately, the mere fact of correlation is not the answer; we seek understanding of the physical linkages. … The new paper provides a clever new idea for a physical linkage, and I anticipate it will get people discussing and studying.”

Any new study concerning climate processes could get sucked into the political vortex enmiring global warming, so we asked if Laepple’s study of Antarctic conditions should lead us to question the widely-accepted theory that burning fossil fuels and changing land use have altered the climate.

Laepple reminded us that he’s studying changes that occur over periods of 10,000 years. He also insists that the new analysis “will not change the basic record of glacial and interglacial periods — the march of ice ages over the past million years. We are focusing on the precession cycle [the 21,000-year cycle affecting the location of Earth's axis], as this provides the evidence showing where and how the climate is affected by radiation changes, and might hold the key to the mechanism of slow climate change.”

Years ago, scientists began to revise their interpretation of Greenland ice to account for the seasonality in snowfall, Laepple says. “This new study is part of a long discussion. As we interpret the climate record, we have to focus more on how the climate signal gets recorded in the climate record.”