On the other end of the spectrum, some crop-based biofuels can actually produce more carbon dioxide emissions overall than fossil fuels, Pavlenko says. That’s frequently the case for biofuels made from palm oil, since growing that crop can decimate rainforests. Even synthetic e-fuels can approach the impact of jet fuel if they’re produced using electricity from fossil fuels.
Today, most commercially available alternative jet fuels are made from fats, oils, and greases. If they’re derived from waste sources like used cooking oils, these fuels reduce carbon dioxide emissions by roughly 70% to 80% compared with fossil fuels.
It’s worth noting that while SAFs can approach net-zero carbon dioxide emissions, burning the fuels still produces other types of pollution, including other greenhouse gases and particulate matter. The fuels can also contribute to formation of contrails, which trap heat in the atmosphere.
What’s next for SAFs?
There are a few other technologies on the table for cutting climate impacts in aviation, including hydrogen- and battery-powered planes. However, without further technical progress, these options may be limited to smaller planes flying shorter routes, and most global carbon dioxide emissions today come from flights over about 900 miles (1,500 kilometers). That’s where SAFs could help. Alternative fuels are attractive for the aviation industry because they’re a drop-in solution, requiring little adjustment of aircraft and airport infrastructure. (Planes might need small adjustments to run on 100% SAFs in the future, depending on the mix of chemicals in the fuel.)
Many aviation net-zero plans, like the one published by the International Air Transport Association, assume that SAFs will make up the majority of the industry’s climate progress in the coming decades. Over the past year, several test flights powered by 100% SAFs have taken off. However, alternative fuels made up less than 0.2% of the global jet fuel supply in 2022. So there’s a lot of progress needed to supply alternative fuels that are actually helpful for the climate.
One of the main challenges to getting SAFs into the skies is expanding the supply. While fats, oils, and greases are the basis of most commercially available SAFs today, the world doesn’t eat enough french fries for used cooking oils to meet global jet fuel demand alone. In fact, even with increased collection, waste fats, oils, and greases probably won’t provide more than 5% of global jet fuel supply, Pavlenko says.
Some new biofuels, like those made from agricultural residue, municipal solid waste, and hardy crops like switchgrass, are starting to enter the market; a few facilities are under construction or producing jet fuel from these sources worldwide, and the carbon dioxide emission savings they achieve can range from 50% to 90%.
Recent policy moves in both the US and the European Union are aimed at boosting the market for alternative fuels. RefuelEU Aviation, a deal finalized in April, requires that fuel supply at EU airports include 2% SAFs by 2025 and 70% by 2050. The EU rule will only count SAFs from waste sources, advanced biofuels, and e-fuels, not crop-derived fuels. It also has a specific target for e-fuels that’s aimed at boosting their production.
The US, on the other hand, recently passed new tax credits for alternative fuels, aimed at helping expensive options reach price parity with fossil fuels. The tax credits last until 2027 and apply to any fuel that reduces carbon dioxide emissions by at least 50% compared with fossil fuels, though the details on how reductions are calculated haven’t been released yet.
Ultimately, alternative fuels present one of the most straightforward pathways to cutting the climate impacts from aviation, but only certain types will end up benefiting the climate. “SAFs are a solution, but they need to be very properly done,” Mirolo says. Otherwise, they risk becoming “a cure that’s worse than the disease.”
Matt Kaeberlein is what you might call a dog person. He has grown up with dogs and describes his German shepherd, Dobby, as “really special.” But Dobby is 14 years old—around 98 in dog years.
Kaeberlein is co-director of the Dog Aging Project, an ambitious research effort to track the aging process of tens of thousands of companion dogs across the US. He is one of a handful of scientists on a mission to improve, delay, and possibly reverse that process to help them live longer, healthier lives.
And dogs are just the beginning. One day, this research could help to prolong the lives of humans. Read the full story.
—Jessica Hamzelou
We can still have nice things
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+ All hail the unsung women of indie sleaze. + It’s officially October! + This list of sartorial advice has been entertaining us at MIT Technology Review—how many points do you agree with? + Put down the expired milk, it’s got a whole lot more to give. 🥛 + Some top tips for remembering your dreams more fully: should you want to, that is.
The technology would likely be used first on infants born at 22 or 23 weeks who don’t have many other options. “You don’t want to put an infant on this device who would otherwise do well with conventional therapy,” Mychaliska says. At 22 weeks gestation, babies are tiny, often weighing less than a pound. And their lungs are still developing. When researchers looked at babies born between 2013 and 2018, survival among those who were resuscitated at 22 weeks was 30%. That number rose to nearly 56% at 23 weeks. And babies born at that stage who do survive have an increased risk of neurodevelopmental problems, cerebral palsy, mobility problems, hearing impairments, and other disabilities.
Selecting the right participants will be tricky. Some experts argue that gestational age shouldn’t be the only criteria. One complicating factor is that prognosis varies widely from center to center, and it’s improving as hospitals learn how best to treat these preemies. At the University of Iowa Stead Family Children’s Hospital, for example, survival rates are much higher than average: 64% for babies born at 22 weeks. They’ve even managed to keep a handful of infants born at 21 weeks alive. “These babies are not a hopeless case. They very much can survive. They very much can thrive if you are managing them appropriately,” says Brady Thomas, a neonatologist at Stead. “Are you really going to make that much of a bigger impact by adding in this technology, and what risks might exist to those patients as you’re starting to trial it?”
Prognosis also varies widely from baby to baby depending on a variety of factors. “The girls do better than the boys. The bigger ones do better than the smaller ones,” says Mark Mercurio, a neonatologist and pediatric bioethicist at the Yale School of Medicine. So “how bad does the prognosis with current therapy need to be to justify use of an artificial womb?” That’s a question Mercurio would like to see answered.
What are the risks?
One ever-present concern in the tiniest babies is brain bleeds. “That’s due to a number of factors—a combination of their brain immaturity, and in part associated with the treatment that we provide,” Mychaliska says. Babies in an artificial womb would need to be on a blood thinner to prevent clots from forming where the tubes enter the body. “I believe that places a premature infant at very high risk for brain bleeding,” he says.
And it’s not just about the baby. To be eligible for EXTEND, infants must be delivered via cesarean section, which puts the pregnant person at higher risk for infection and bleeding. Delivery via a C-section can also have an impact on future pregnancies.
So if it works, could babies be grown entirely outside the womb?
Not anytime soon. Maybe not ever. In a paper published in 2022, Flake and his colleagues called this scenario “a technically and developmentally naive, yet sensationally speculative, pipe dream.” The problem is twofold. First, fetal development is a carefully choreographed process that relies on chemical communication between the pregnant parent’s body and the fetus. Even if researchers understood all the factors that contribute to fetal development—and they don’t—there’s no guarantee they could recreate those conditions.
The second issue is size. The artificial womb systems being developed require doctors to insert a small tube into the infant’s umbilical cord to deliver oxygenated blood. The smaller the umbilical cord, the more difficult this becomes.
What are the ethical concerns?
In the near term, there are concerns about how to ensure that researchers are obtaining proper informed consent from parents who may be desperate to save their babies. “This is an issue that comes up with lots of last-chance therapies,” says Vardit Ravitsky, a bioethicist and president of the Hastings Center, a bioethics research institute.
Last week, Elon Musk made the bold assertion that sticking electrodes in people’s heads is going to lead to a huge increase in the rate of data transfer out of, and into, human brains.
The occasion of Musk’s post was the announcement by Neuralink, his brain-computer interface company, that it was officially seeking the first volunteer to receive an implant that contains more than twice the number of electrodes than previous versions to collect more data from more nerve cells.
The entrepreneur mentioned a long-term goal of vastly increasing “bandwidth” between people, or people and machines, by a factor of 1,000 or more. But what does he mean, and is it even possible? Read the full story.
—Antonio Regalado
This story is from The Checkup, MIT Technology Review’s weekly biotech newsletter. Sign up to receive it in your inbox every Thursday.
Everything you need to know about artificial wombs
Earlier this month, US Food and Drug Administration advisors met to discuss how to move research on artificial wombs from animals into humans.
These medical devices are designed to give extremely premature infants a bit more time to develop in a womb-like environment before entering the outside world. They have been tested with hundreds of lambs (and some piglets), but animal models can’t fully predict how the technology will work for humans.
