Population growth, now at roughly 78 million extra people per year, is the don't-go-there zone of modern environmentalism and political discourse.

But let's go there for the moment: The biodiversity crisis. The water crisis. The climate crisis. Lurking behind all these crises is at least one shared factor: human population. Species extinction? Think land clearing for agriculture to feed a growing population of 6.8 billion people. Water? The majority of water goes directly to growing that same food supply. And giving a helping hand to all these other crises as a result of all the fossil fuel burning needed to power our lives and lift billions out of poverty: anthropogenic climate change.

BALTIMORE—In the decades-long war on cancer, as of late, researchers had been making little progress in comparison to colleagues treating other conditions, such as cardiac or infectious diseases. "Cancer research has really plateaued out," William Matsui, an associate professor of oncology at Johns Hopkins University's School of Medicine, said at the 2009 World Stem Cell Summit here on Tuesday. But pushing cancer stem cell research "gives us a novel way to study cancer," said Matsui, who also runs a lab at the university's Sidney Kimmel Comprehensive Cancer Center.

Cancer and stem cells have had a fraught relationship—not in the least because of early concern that stem cell treatments could in fact spur on cancer through their encouragement of undifferentiated cell growth. But cancer stem cells themselves have gained a more solid toe-hold in the past several years as a potential new target for cancer research.

President Obama gave his first major speech on climate change today at the United Nations, part of a special session convened by U.N. Secretary General Ban Ki-moon. The reason for the session? Lack of speed in international negotiations to address climate change.

You can see the president's speech here:

In addition to reaffirming the U.S. commitment to addressing climate change, the president listed some recent accomplishments: new efficiency standards for all vehicles, billions of dollars for renewable energy development, and the nation's first mandatory greenhouse gas reporting system. He even noted a plan to work with the world's other largest economies, known as the G20, to "phase out fossil-fuel subsidies so that we can better address our climate challenge."

“Are you ready?” the young driver beside me asked, as we sat in the two-seat Tesla Roadster convertible, facing a straight, steep, quarter-mile road that rises from the water of San Francisco Bay up the headland to the Golden Gate Bridge. Then he floored the accelerator. I was driven into the seat-back behind me—and I mean driven, like I was strapped into some insane amusement park ride—for several full seconds as the car accelerated and accelerated like a rocket up the climb. Only there was no screaming flame blasting behind us. There was no engine roaring either. I was being shot up this road so fast my emergency senses were on full alert, yet all was eerily quiet.

The Tesla Motors roadster is an all-electric vehicle. Which means zero emissions. There’s no engine, no fuel tank, just a deep bank of lithium-ion batteries and a single-gear, direct-drive motor that hits maximum torque instantly (that’s the beauty of electric propulsion). The car is blistering fast; the sport edition goes from zero to 60 miles per hour in 3.7 seconds. Not up on car specs? The Chevy Corvette, with a monster 6.2 liter, eight cylinder, 430 horsepower engine takes 4.6 seconds. The Tesla accelerates faster than the Porsche 911. Faster than the Ferrari Spider. The typical sedan takes a good 6.0 seconds or more to reach the same speed.

Editor's Note: A team of Rensselaer Polytechnic Institute students are traveling up New York's Hudson River this week on the New Clermont, a 6.7-meter boat outfitted with a pair of 2.2-kilowatt hydrogen fuel cells to power the boat's motor. Their journey began September 21 from Manhattan's Pier 84 and will cover 240 kilometers (at a projected speed of 8 kilometers per hour). After making several stops along the way, the crew expects to arrive back at Rensselaer Polytech's campus in Troy, N.Y., on September 25. This is the first of Scientific American.com's blogs chronicling this expedition, called the New Clermont Project.

The New Clermont Project comes 200 years after Robert Fulton drove the world's first commercial steamboat, The Clermont, from New York to Albany. William Gathright, a doctoral student in Rensselaer's Materials Science and Engineering Department, began assembling the crew and resources necessary for this green-fueled tour of the Hudson earlier this year. Gathright is also pursuing a master's in management from Rensselaer's Lally School of Management & Technology.

Paying bills or counting change may seem like basic life skills to most, but for those who are about to slip into older-age dementia, the tasks can become increasingly difficult. And as fiscal functionality begins to fail, Alzheimer's disease might be less than a year away, a new study suggests.

"Impairments in financial skills and judgments are often the first functional changes demonstrated by patients with incipient dementia," wrote the authors of the paper, which was published online today in Neurology. 

Although the relationship between money management skills and dementia has been established for some time, the researchers' focus on declining skills as an early indicator showed that once these abilities start to slip, the diagnosable disease is likely not far behind.

Martin Campbell-Kelly’s September article on the origins of computing traces the history of machine computation from Charles Babbage, the 18th century British mathematician, through the 20th century. Yet according to many of our readers, we made a critical omission.

John Hauptman, a professor of physics at Iowa State University, writes:

The first person to build and operate an electronic digital computer was a physics professor, as correctly noted in your excellent article “Dr. Atanasoff’s Computer,” Scientific American, August 1988 [not online]. Atanasoff’s first computer was a 12-bit 2-word machine running at 60Hz wall-plug frequency and could add and subtract binary numbers stored in a regenerative memory using a logic unit built with seven triode tubes. This was 1937. There was no war, no Pearl Harbor, just a theoretical physicist trying to solve problems in quantum mechanics with his students at Iowa State College in Ames, Iowa.

The ethics of enhanced interrogation techniques, detailed in a series of White House memos earlier this year, have come under growing fire in Washington and around the world. And the effectiveness of these practices—including sleep deprivation and waterboarding—have drawn increasing scrutiny in the scientific community.

A new review paper, published online today in Trends in Cognitive Science, investigates whether such intense approaches, labeled as torture by some, might be counterproductive to obtaining accurate information from suspects.

The use of coercive interrogation "is based on the assumption that subjects will be motivated to reveal veridical information to end interrogation, and that extreme stress, shock and anxiety do not impact memory," Shane O'Mara, a professor at the Trinity College Institute of Neuroscience in Dublin and the paper's lead author, said in a prepared statement. "However, this model of the impact of extreme stress on memory and the brain is utterly unsupported by scientific evidence."

Runoff from agriculture is the biggest polluter of the country's river and stream water, according to the U.S. Environmental Protection Agency (EPA), and it has been fingered for hypoxic dead zones and toxic red tide algae blooms.

But how much of that runoff makes it into people's drinking water closer to home? In agricultural areas, it can be enough to cause persistent health problems, including diarrhea and other infections, according to a report today in The New York Times.

"Sometimes it smells like a barn coming out of the faucet," Lisa Barnard, a Wisconsin resident told the Times. Barnard's well water tested positive for various contaminants and bacteria, including E. coli—which point not just to any runoff, but that coming from excess manure, according to the Times piece.

You really can drive across the country on algae--and a 700-pound battery pack--or so proved the crew behind the documentary Fuel . Embarking on September 8 and pulling into New York City today, just in time for the film's premiere, the Algaeus covered 3,750 miles.

"It got 147 miles per gallon in the city," says Fuel director Josh Tickell of the converted to plug-in Prius hybrid that he drove on a mix of battery power and algae fuel blended with conventional gasoline. The Algaeus did less well on the highway: 52 mpg, because of the lack of regenerative braking that recharges the battery, among other things.