As my devoted readers no doubt realize by now, I’m on a bit of a Rachel Carson kick. I wrote a blog post and produced a radio show about her last fall, and I’m working on an article about her for Johns Hopkins magazine (Carson got her master’s degree at Hopkins). Why this slight Carson obsession? It started with the 50th anniversary of Silent Spring, which got me wondering, as a science writer, how someone armed only with scientific knowledge and words could have such influence. I believe we science writers sometimes sell ourselves short in terms of what we can accomplish, especially in this age of disposable Web writing. Carson can remind us of the potential of writing for impact, not just for mouse clicks.
In 1953, Rachel Carson spoke at a symposium at the American Association for the Advancement of Science’s annual meeting. The topic was the sea frontier. Unlike the other eight panel members with whom she shared a stage, Carson was not a research scientist; she had until recently worked as a staff writer for the US Fish and Wildlife Service. (She was also the only woman on the panel).
At the conference she talked about the book she was writing, The Edge of the Sea, which would be based mainly on her observations, and less on the work of other scientists, as her previous books had been. Carson had scientific training, but it was her writing that earned her the speaking slot: her 1951 book The Sea Around Us had made her the nation’s most famous writer about the oceans and perhaps about all of science.
Although Rachel Carson spent almost her entire career writing about the sea, she is remembered today for her one book about things that happen on land. That book, Silent Spring, awoke the American public to the dangers of many common pesticides, and launched the environmental movement. But while the birth of environmentalism would not have happened exactly when it did and how it did without Carson’s advocacy, it would have happened: Americans would not have tolerated smoggy cities, burning rivers, and toxic chemical clouds for much longer. “I suspect that the audience [of Silent Spring] was close to an environmental awakening,” said Jane Lubchenco, a marine biologist and past head of the US National Oceanic and Atmospheric Administration, at a symposium dedicated to Carson at this year’s AAAS meeting. “No doubt [Carson] catalyzed it, but the ground was fertile.”
Up until around 500 million years ago, the continents of Earth were practically lifeless, harboring – at most – slimy mats of bacteria on rocky, barren wastelands. Around this time plants began to creep out of the oceans, gradually developing adaptations that allowed them to expand further and further inland over millions and millions of years. But there is a dark side to this story: the increasing success of plants on land may have contributed to one of the largest set of extinctions known to the fossil record.
Plants colonized land over a period as long as tens to hundreds of millions of years. But there were a number of evolutionary advances that brought about swift change. Each advance allowed plants to either expand to new habitats or grow larger. And with each advance, the roots of these pioneering plants broke more and more earth apart. To Tom Algeo, a geologist at the University of Cincinnati, this process may have created a chain of events that removed massive quantities of oxygen from the ocean.
Although the first land plants evolved around 500 million years ago, they remained close to the waters edge and did not grow very large for around 100 million years. But these early plants paved the way for the future success of larger plants. This later success is largely due to lignin, tissue that gives plants structure and support.
Author’s note: This post is the first in a series of great Earth history moments. Stay tuned for a new post every other week.
Around 6 million years ago, the Mediterranean Sea became separated from the Atlantic. Cut off from the world’s oceans, it began to evaporate. By 5.3 million years ago, there was literally no sea left. 1000 years later, it was refilled in a geologic instant.
A number of discoveries led to the conclusion that the Mediterranean dried out completely sometime in the past. The first came in the 1960s, when seismic studies of the floor of the Mediterranean revealed a unique layer – dubbed the M reflector – across the whole basin. Scientists interpreted it to be a large layer of salt distributed evenly across the seafloor.
Later, in 1970, a leg of the Deep Sea Drilling Project cored deep into the Mediterranean seabed. They found what the seismic data predicted: a hard layer of evaporites – rocks composed of salts.
The only way to get evaporite rocks at the base of a sea is to evaporate water until it becomes so concentrated with salts that they can no longer be dissolved. This forces them to precipitate into a solid form.
Just as enigmatic as the salt layer, engineers mapping the base of the Nile River in preparation for the construction of the Aswan Dam around this time found that carved deep beneath the silty floor of the Nile was a canyon whose ancient base was well below sea level.
The only way for a canyon to be carved into bedrock is for a river to flow through it. But a river won’t cut lower than sea level. This deep canyon meant that Medteranian sea level must have been dramatically lower in the past.
In 1972, Kenneth Hsu, the primary investigator on the Deep Sea Drilling Leg that cored the Mediterranean, authored a paper in Nature concluding that the sea must have evaporated nearly completely to produce such an anomalous layer of evaporite minerals and to have cut canyons so deep. In the paper he admitted it was a “preposterous idea,” but stated that no other explanation presented itself. Read the rest of this entry »
Sebastian Seung could have hired an army of undergraduates to do crucial legwork in his neuroscience lab at MIT. Even with the help of powerful computers that would have taken years. Instead, he and his lab turned it into a game, called it Eyewire, and 10,000 people played it on the first day. Many are still at it. These players hold all conceivable occupations, but in their free time they are neuroscientists: a prime example of scientists partnering with the public in citizen science projects. Collecting or organizing vast amounts of data might take one or two scientists years, but with thousands of people helping, data sets are complete in months or weeks, and discovery accelerates.
The goal of Eyewire is to trace individual neurons in the the tangles of a mouse’s retina. Many people map the same neuron, and results are averaged for better accuracy. Accuracy against the average wins points, though sometimes a player has to be the trailblazer, the first one to map a new neuron, slowly expanding the map. Collectively, the players turn tangles into data, mapping neuron types, connections, and extensions. Seung is hoping to map the retina as a stepping stone to mapping the whole brain, developing a set of connections he thinks may be unique to each person. This connectome, he says, may make each of us who we are. But to map this vast connectome, the pathways of billions neurons in each person’s head, Seung needed help from both a powerful artificial intelligence, the computer game, and thousands of citizen scientists around the world playing it.
If you’re a writer looking for a good symbol, consider the tree. The author of Genesis did, twice: he placed the tree of life and the tree of knowledge front and center in the Garden of Eden. Homer did, too: When his hero Odysseus returned home after twenty years of war and travel, needing to prove his identity to his skeptical wife, Penelope, he used a tree. “Move our bed into the hallway,” Penelope told her servant, laying a trap. (I’m paraphrasing here.) “It can’t be done,” Odysseus protested. “I carved a post of that bed from a living olive tree.” Only then did Penelope believe the strange man was really her husband, as steady as that post.
Trees have long impressed us with their steadfastness; in fact, some trees from Biblical times are still with us today. But a new story I read recently casts trees in a different role. I first came across a version of this story in a paper published in the journal BioScience in 2007. The authors looked at where trees live using a tool known as a “climate envelope,” which is a line drawn on a map around the entire range where a given species is able to survive. The scientists compared climate envelopes for 130 trees under 2007 conditions to those predicted for the end of the century, using the same computer models that the UN’s Intergovernmental Panel on Climate Change bases its forecasts on. On average, they found that trees’ envelopes moved 700 kilometers north, nearly the distance from Memphis to Chicago.
So does that mean our trees will be moving north as things get warmer? Traveling trees can make great stories: Shakespeare’s Macbeth was vanquished when Birnam Wood moved a few miles to his fortress at Dunsinane Hill. And it would be dramatic indeed if future northern woodsmen and women hunt deer among sprawling live oaks and big-leaf magnolias instead of spruce and pine trees. But the scientists who wrote the BioScience paper noted that actual trees are unlikely to track their climate envelopes’ northward migration in the coming years, at least if unassisted by humans. Trees can “move” up to a few miles in a generation, by setting their seeds aloft in the wind or encasing them in a shell so they can survive a trip in the gut of an animal. But tree generations are long, and most seeds land close to home. Sugar maples, for example, lead a chaste adolescence, and don’t start making seeds until the age of 22 or so. They then send out seeds attached to little helicopters, which spin and float at most the length of a football field before touching down. Scientists estimate trees’ maximum migration rate to be around 50 kilometers per century, with many traveling far slower—a tortoise’s pace in this race.
The rainforests of Madagascar highlight, with great clarity, the power the physical environment exerts on evolution. As a study abroad student in the fall of 2006, I was researching the sleep habits of the brown mouse lemur in Ranomafana National Park, a protected tract of land in the high rain-forested mountains of Madagascar’s east coast.
During the day, I bushwhacked through this dense rainforest, attempting to locate two or three of these nocturnal mouse lemurs, who had been fixed with tracking collars, as they slept. In the evening, I waited for the lemurs to wake up so that I could record the size and consistency of their sleeping groups.
One day, as the sun was setting on the bamboo, ferns, and mossy trees of the forest, I watched as multiple lemurs suddenly emerged and attempted to rouse the female lemur I was tracking from her sleep. These lemurs, all male, were attempting to mate with my study subject.
Female brown mouse lemurs, and indeed many species of female lemurs in Madagascar, are only receptive to mating for a very short period of time each year. To make the most of this short mating season, the male lemurs, deathly focused on a single goal, spend the winter months growing testicles that end up being a quarter of their entire body mass. It is no question, given the males’ months of stored hormonal energy, that there would be a significant interest in my study subject that day. Read the rest of this entry »
An Ecologist’s Battle
Invasive plants are the ones that don’t play well with others. They steal their neighbors’ food and water, and they refuse to share. And you’ll see them all around the Baltimore area: vines smothering stream banks and blanketing entire trees; the brambles tangling and choking the understory; the annuals carpeting the forest floor. They’re the botanical version of an alien invasion.
Or, they can make nice additions to our gardens. Vanessa Beauchamp, an invasive plant ecologist, tells me about a hiker who came upon her research team in a park outside Baltimore. “She asked us what we’re doing, and we explained we’re studying this invasive grass that we think is a really big problem, and we’re trying to understand more about its ecology. And she says, ‘Oh my gosh that stuff is so pretty, I dug up a bunch and planted it in my yard.’”
The plant was wavyleaf basketgrass, a native of Europe and Asia. It sounds innocent enough, like a prairie grass that might rustle softly in a summer breeze. And it’s pretty enough, too, with intensely green leaves that unfurl on either side of a central shoot, and a head of spiky seeds that sticks up a foot or so above the ground. The seeds are the problem, though—they hitch rides on pant legs, animals, basically anything that comes by—and disperse to new locations that way. The plant can grow just fine even in the deep shade of a mature forest. In Patapsco Valley State Park, where it was discovered in the mid-1990s, it now carpets acres of forest floor. The Maryland Department of Natural Resources launched a war on it but lost, due to lack of funding. Now the plant has spread to other parks in the area, and experts like Beauchamp fear there may be no containing it.
But if it’s green and pretty, what’s the worry? Beauchamp says it’s all about the community of life in the forest. Exotic plants like basketgrass are newcomers to this community, so nothing has evolved to eat them—a lesson Beauchamp has learned firsthand. “When we worked on wavyleaf basketgrass, we literally spent the summer crawling around on the forest floor. I figured we would just be tick city,” she says. Instead, of the half dozen people on her crew, “We got one tick between all of us. I mean, that’s insane.”
Few of us would be sad to see the ticks disappear. But without the thousands of insects, worms, mites, and spiders that make their living in the forest understory, the woods would be a vastly different—and less lively—place. “Nobody’s looked at how insects are able to use this grass…We see very little insect damage on the grass at all. We see no deer damage,” says Beauchamp. “If there’s no insects eating them, there’s no birds eating those insects, and up and up and up.”
A wavyleaf basketgrass army
Beauchamp moved to Towson University in Baltimore from Arizona five years ago. For an invasive species expert, the move meant more than packing and unpacking boxes—it meant abandoning one biome and learning a new one. Luckily for Beauchamp, Maryland has no shortage of invasive plants, and it didn’t take her long to find one she could claim as her own. “I came across this wavyleaf basketgrass that nobody knew anything about, and I said ‘All right. That’s mine.’”
One of the questions Beauchamp is asking is how aggressive the grass actually is. Many writers on the Web claim it crowds out other plant species, but Beauchamp wonders whether it might just take advantage of openings on the forest floor, especially those created by Maryland’s massive plant-munching deer population. To test how competitive wavyleaf basketgrass is, her research team is growing the grass in a greenhouse alongside other native and invasive grasses, and seeing which puts on the most weight. They hope to have results soon.
Beauchamp is also trying to figure out how the seeds disperse. And she thinks she’s found a suspect: pet dogs. When hikers let their dogs run through a basketgrass patch, they “come out looking like a chia pet,” says Beauchamp. Fore more precision, she had her students count the number of seeds sticking to a dog. “We found that a single dog going through this grass for 30 seconds can get over 2000 seeds on it,” she says.
Dogs may not be the only culprit, though; Beauchamp also has her eye on deer. She and her team tested this hypothesis in a rather macabre way: they got severed deer legs from a meat processor, and “walked” the legs through a basketgrass patch. Again, the legs came out covered in seeds.
But Beauchamp admits she can’t answer the most important questions: how much wavyleaf basketgrass is there, and where? “I have absolutely no number to tell you in terms of how many acres this grass covers in Maryland,” she say. “None.” Unfortunately, when she wrote a grant to fund a project that would get at such a number, she got caught in a chicken-and-egg situation: the review panel rejected the proposal, saying Beauchamp and colleagues hadn’t demonstrated how much of a threat the grass poses. “But if I don’t have any money to study it, how can I demonstrate that?” she asks.
So like any good scientist, she’s gotten creative. She mustered a “wavyleaf basketgrass army” of undergraduates and high school teachers to go out and count plants in different locations. She’s also teaming with a Catonsville Community College professor who’s developing a smartphone app that will allow anybody to report a basketgrass sighting, along with GPS coordinates. Beauchamp is hoping the data her team and concerned citizens collect will convince funders and policymakers that the grass is worth studying on a larger scale.
Beauchamp vs. basketgrass
Beauchamp versus basketgrass is the latest chapter in a long saga of human battles against invasive plants. And so far the invaders have scored most of the victories. Here in Maryland, English ivy, Japanese stilt-grass, mile-a-minute weed (an Asian species known as “kudzu of the north”), and other exotics have become far more familiar sights in our parks and forests than most of our native plants. Will wavyleaf basketgrass join this list of dubious characters, or could this be the time we outsmart the weed?
(All photos courtesy of Vanessa Beauchamp)
E. B. White wrote, “It is a miracle that New York works at all. By rights New York should have destroyed itself long ago, from panic or fire or rioting or failure of some vital supply line in its circulatory system.” On Monday, Hurricane Sandy managed to cut off many of New York’s supply lines in ways they’ve never been tested before. The city lost power, water, and lives. But it was not only White’s fears, but also the predictions of scientists that were realized. Two separate papers, published earlier this year and last, predicted what would happen to New York City if it were struck by a severe storm.
In 2011, a state agency assembled a massive report on climate change in New York. In it, Klaus H. Jacob, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory, conducted a case study (PDF) on the impact of a 100-year flood on New York City’s transportation system. A 100-year flood is a flood whose severity, on average, is seen only once every hundred years (or has a 1 percent chance of occurring in any given year), which the study equates with a category 1 to 2 hurricane. Jacob looked at three scenarios: a 100-year flood alone, one combined with a 2-foot sea level rise, and another with a 4-foot sea level rise as a result of climate change.
Jacob identified the areas that would be flooded under each scenario. Using a base flood elevation map of the city as well as known elevations of transportation structures, he found that low-lying streets, subways, and tunnels in the Battery, Jamaica Bay, the Rockaways and other neighborhoods near the city’s shoreline would be particularly vulnerable to flooding. Indeed, those areas were among those that suffered most from Hurricane Sandy. In fact, a record 14 feet, or 4.25 meters, of water swept over the Battery on Monday, matching the case study’s worst-case scenario. Jacob also predicted that the total economic and physical damages for NYC would be $58 billion, $70 billion, and $84 billion in order of worsening scenario. One current estimate stands at $20 billion in losses for the entire Northeast and Mid-Atlantic due to Sandy, so Jacob’s estimates seem to have overshot it. One thing is for sure though. Investing in infrastructure that protect the city from future storms can save money in the long run. As Jacob told New York Magazine, “For every dollar that you spend today, you probably save $4 of not incurred costs later.”
Just months after Jacob’s case study, Ning Lin, a climate scientist at MIT, and colleagues used computer models to predict the impact of a hurricane on New York City. Published in Nature Climate Change in February this year, the study used four climate models to simulate 10,000 synthetic storms, half under the current climate and half under projected warming conditions. The researchers programmed the storm to be within a 200-km radius from the Battery and to gust at wind speeds greater than 20 m/s, or 45 mph (Hurricane Sandy exceeded the models, with 60 mph recorded at Central Park). They found that in the worst-case scenarios, a hurricane would cause a storm surge as high as 4.57 m to 4.75 m at the Battery, which came fairly close to the 4.25 m caused by Sandy.
The researchers also found that climate change will only increase the risk of storm surges for the city. Based on historical data on NY-region storms, they predicted that a 1 m rise in sea level in the future will increase the likelihood of a 100-year surge flood occurring as frequently as every 3-20 years and a 500-year flood every 25-240 years by the end of the century. Of course, predicting something as unpredictable as a hurricane is extremely difficult. But the fact that the climate models closely mirrored Hurricane Sandy makes the need to prepare for future severe weather all the more urgent.
Climate science is an extremely complicated discipline. Climate change skeptics and deniers, I believe, thrive on this complexity. They highlight what is not known or not agreed upon to suggest that the discipline as a whole is flawed. The best way to combat such an argument is with simplicity.
In that light, I present a simple, four-point argument demonstrating the reality of anthropogenic global warming.
Carbon Dioxide Causes Warming
The central mechanism driving anthropogenic climate change is the combustion of fossil fuels. Fossil fuels, the chemicals we use to heat our houses and move our cars, are compounds formed when ancient organic material, predominantly the remains of algae, is buried and cooked at a high temperature and pressure for millions of years. The result is a set of carbon-based chemicals that release a lot of energy, and form carbon dioxide (CO2), when burned.
This CO2, when released into the atmosphere, traps heat by blocking the escape of Earth’s radiation into space. (Anything that has a temperature, Earth included, produces radiation.) Known as the greenhouse effect, this is not a new or controversial idea. In 1861, John Tyndall, a British professor of natural philosophy, gave a lecture titled “On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation Absorption and Conduction.” Tyndall demonstrated conclusively that CO2, among other gasses, absorbs long wave radiation – the same type that Earth emits to space. His experiment was simple. Tyndall produced radiation with a bunson burner, knowing that the heat would emit a full spectrum of wavelengths, including long-wave radiation. He then measured those wavelengths after passing them through different gasses. Because not all wavelengths traveled through the CO2, Tyndall concluded that the CO2 must be absorbing some of the heat. This simple experiment has huge implications for our planet.
Tyndall’s work greatly influenced a Swedish physicist named Svante Arrhenius. In 1896, Arrhenius published a paper titled “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground.” (Carbonic acid was what carbon dioxide was called at the time.) Arrhenius, in essence, took Tyndall’s work out of the lab and applied the concept to the real world. Instead of a bunson burner, he used observations of infrared radiation from the moon. Because he knew that the moon, without an atmosphere, should transmit all of its long wave radiation to Earth, he was able to calculate the effect our atmosphere had on it by documenting which wavelengths didn’t make it. For each lunar observation, he compared that data with atmospheric conditions (humidity and CO2 levels) to see what effect they had on the radiation that made it to Earth. By doing this he determined that with a rise in CO2 came a “nearly arithmetic” rise in temperature. Using his calculations he determined that a doubling of atmospheric CO2would result in a 5ºC temperature rise. Even with the advent of massive computer models and high-tech lab equipment, this value is still in agreement with modern climate science.
Both Tyndall and Arrhenius speculated that CO2 has played a role in controlling the Ice Ages. Arrhenius, back in 1896, even predicted that human fossil fuel use might result in future global warming.
Carbon Dioxide Concentrations in the Atmosphere are Increasing
This is the easiest point to make. Scientists can measure the amount of CO2 in the atmosphere. It is increasing.
The best evidence is the famous “Keeling Curve.” In 1958, Charles Keeling, a professor of oceanography at Caltech, began making continuous measurements of CO2 on the peak of the big Island of Hawaii. Because this station is far away from major urban centers, and because the station is at a high altitude, the location is perfect for making CO2 measurements that are representative of the whole atmosphere. His measurements, which continue to this day, show a progressive rise in CO2from around 315 parts per million in 1958 to about 394 ppm as of September 2012.
The Increased Carbon Dioxide is Coming from Human Activity
This is the heart of the controversy, but this is just as easy to demonstrate as the previous two points. The CO2 that is associated with the recent increase has a chemical signature that unequivocally ties it to human activity.
CO2 can come from a variety of sources. CO2 in the ocean is constantly exchanged with CO2 in the atmosphere; there is CO2 in the mantle, which can be released through volcanoes, and wildfires can release CO2 the same way that burning fossil fuels does. By looking at the carbon contained in CO2, scientist can distinguish between each of these sources.
Fossil fuels come from the cooked remains of ancient life. Therefore, the carbon in this CO2 must be derived from the remains of living things that existed a very long time ago. Both the age and the source of carbon can be inferred using chemical entities known as isotopes.
Elements like carbon can have differing masses, caused by changes in the number of neutrons in the atom. These are called isotopes, and each isotope acts a bit differently. When a plant takes in CO2 from the atmosphere through photosynthesis, it prefers carbon with a mass of 12 to carbon with a mass of 13. Therefore, anything that photosynthesizes, or anything that eats something produced by photosynthesis (essentially all life on this planet), is composed of less carbon-13 than is typically found in the atmosphere. This is the signature of carbon that comes from living things. Life, both alive and transformed into fossil fuels, represents a massive reservoir of carbon-12. If this kind of carbon were released into the atmosphere, the concentration of carbon-13 in the atmosphere would be reduced by dilution with carbon-12.
Carbon can also have an isotope with a mass of 14. This type of carbon is created in the atmosphere continuously. Because of this, there is a constant source of carbon-14 on the surface of Earth. Unlike carbon-13, carbon-14 is radioactive. This means that it cannot remain carbon-14 forever. It slowly decays away at a known rate. This property allows scientists to use carbon-14 to date once living things, but anything past approximately 60,000 years, cannot be dated since it will have virtually no carbon-14 left. A complete lack of carbon-14 is the signature ancient carbon. If enough of it is released to the atmosphere, it will decrease the relative concentration of carbon-14 in the atmosphere by diluting it with carbon-14 free CO2.
The combustion of fossil fuels, then, should reduce the concentration of both carbon-13 and carbon-14 in the atmosphere.
Both are happening. They are known collectively as the Suess effect. The concentration of carbon-14 and carbon-13 in the atmosphere is declining, and it is declining at the same time that CO2 is increasing. This means that the CO2 increase we are seeing must come from ancient, organic carbon.
No other source of CO2 could have this signature. Wildfires can’t because the carbon being burned is young; it has plenty of carbon-14. Carbon from the ocean has the same problem – too young, too much carbon-14. CO2 from volcanoes does not work either. This carbon does not come from once living matter, so it has plenty of carbon-13.
Carbon derived from the remains of ancient life buried deep inside our Earth is the only plausible source. The only way to release a great deal of it at once is to dig it up and burn it, as humans are doing today.
Average Global Temperatures Are Rising
Just like CO2 concentrations, scientists are able to measure air temperature – in fact the technology has been around for quite a while. The real challenge is getting past the variability, which is the result of things like el Nino and other short term weather patterns, to figure out what the long-term temperature trend is globally. There are plenty of studies showing that the trend is overall warming, but I will highlight a study by Richard Muller.
Richard Muller was an outspoken climate change skeptic, and the Koch brothers, prominent right-wing political figures who deny climate change, funded his research. He gathered as much data as possible and corrected for all known biases – the fact that temperatures are generally higher in cities, for example – and plotted average temperature since 1750. They are rising – a full degree since 1900. A degree may not sound like much, but a rise of 2 degrees would result in ~3 meters of sea level rise, according to a collection of recent estimates. Most of New York City would be underwater.
Carbon dioxide in the atmosphere can warm our planet. This has been taken as fact for well over a century – well before any widespread scientific conspiracy would have been hatched. Carbon dioxide is increasing – it’s real hard to argue with measurements. The increase in carbon dioxide is changing the chemical composition in the atmosphere in a way only fossil fuels are able to. Also, the planet is warming.