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Updated: 23 hours 31 min ago

On-chip optical filter processes wide range of light wavelengths

Wed, 08/01/2018 - 4:59am

MIT researchers have designed an optical filter on a chip that can process optical signals from across an extremely wide spectrum of light at once, something never before available to integrated optics systems that process data using light. The technology may offer greater precision and flexibility for designing optical communication and sensor systems, studying photons and other particles through ultrafast techniques, and in other applications.

Optical filters are used to separate one light source into two separate outputs: one reflects unwanted wavelengths — or colors — and the other transmits desired wavelengths. Instruments that require infrared radiation, for instance, will use optical filters to remove any visible light and get cleaner infrared signals.

Existing optical filters, however, have tradeoffs and disadvantages. Discrete (off-chip) “broadband” filters, called dichroic filters, process wide portions of the light spectrum but are large, can be expensive, and require many layers of optical coatings that reflect certain wavelengths. Integrated filters can be produced in large quantities inexpensively, but they typically cover a very narrow band of the spectrum, so many must be combined to efficiently and selectively filter larger portions of the spectrum.

Researchers from MIT’s Research Laboratory of Electronics have designed the first on-chip filter that, essentially, matches the broadband coverage and precision performance of the bulky filters but can be manufactured using traditional silicon-chip fabrication methods.

“This new filter takes an extremely broad range of wavelengths within its bandwidth as input and efficiently separates it into two output signals, regardless of exactly how wide or at what wavelength the input is. That capability didn’t exist before in integrated optics,” says Emir Salih Magden, a former PhD student in MIT’s Department of Electrical Engineering and Computer Science (EECS) and first author on a paper describing the filters published today in Nature Communications.

Paper co-authors along with Magden, who is now an assistant professor of electrical engineering at Koç University in Turkey, are: Nanxi Li, a Harvard University graduate student; and, from MIT, graduate student Manan Raval; former graduate student Christopher V. Poulton; former postdoc Alfonso Ruocco; postdoc associate Neetesh Singh; former research scientist Diedrik Vermeulen; Erich Ippen, the Elihu Thomson Professor in EECS and the Department of Physics; Leslie Kolodziejski, a professor in EECS; and Michael Watts, an associate professor in EECS.

Dictating the flow of light

The MIT researchers designed a novel chip architecture that mimics dichroic filters in many ways. They created two sections of precisely sized and aligned (down to the nanometer) silicon waveguides that coax different wavelengths into different outputs.

Waveguides have rectangular cross-sections typically made of a “core” of high-index material — meaning light travels slowly through it — surrounded by a lower-index material. When light encounters the higher- and lower-index materials, it tends to bounce toward the higher-index material. Thus, in the waveguide light becomes trapped in, and travels along, the core.

The MIT researchers use waveguides to precisely guide the light input to the corresponding signal outputs. One section of the researchers’ filter contains an array of three waveguides, while the other section contains one waveguide that’s slightly wider than any of the three individual ones.

In a device using the same material for all waveguides, light tends to travel along the widest waveguide. By tweaking the widths in the array of three waveguides and gaps between them, the researchers make them appear as a single wider waveguide, but only to light with longer wavelengths. Wavelengths are measured in nanometers, and adjusting these waveguide metrics creates a “cutoff,” meaning the precise nanometer of wavelength above which light will “see” the array of three waveguides as a single one.

In the paper, for instance, the researchers created a single waveguide measuring 318 nanometers, and three separate waveguides measuring 250 nanometers each with gaps of 100 nanometers in between. This corresponded to a cutoff of around 1,540 nanometers, which is in the infrared region. When a light beam entered the filter, wavelengths measuring less than 1,540 nanometers could detect one wide waveguide on one side and three narrower waveguides on the other. Those wavelengths move along the wider waveguide. Wavelengths longer than 1,540 nanometers, however, can’t detect spaces between three separate waveguides. Instead, they detect a massive waveguide wider than the single waveguide, so move toward the three waveguides.

“That these long wavelengths are unable to distinguish these gaps, and see them as a single waveguide, is half of the puzzle. The other half is designing efficient transitions for routing light through these waveguides toward the outputs,” Magden says.

The design also allows for a very sharp roll-off, measured by how precisely a filter splits an input near the cutoff. If the roll-off is gradual, some desired transmission signal goes into the undesired output. Sharper roll-off produces a cleaner signal filtered with minimal loss. In measurements, the researchers found their filters offer about 10 to 70 times sharper roll-offs than other broadband filters.

As a final component, the researchers provided guidelines for exact widths and gaps of the waveguides needed to achieve different cutoffs for different wavelengths. In that way, the filters are highly customizable to work at any wavelength range. “Once you choose what materials to use, you can determine the necessary waveguide dimensions and design a similar filter for your own platform,” Magden says.

Sharper tools

Many of these broadband filters can be implemented within one system to flexibly process signals from across the entire optical spectrum, including splitting and combing signals from multiple inputs into multiple outputs.

This could pave the way for sharper “optical combs,” a relatively new invention consisting of uniformly spaced femtosecond (one quadrillionth of a second) pulses of light from across the visible light spectrum — with some spanning ultraviolet and infrared zones — resulting in thousands of individual lines of radio-frequency signals that resemble “teeth” of a comb. Broadband optical filters are critical in combining different parts of the comb, which reduces unwanted signal noise and produces very fine comb teeth at exact wavelengths.

Because the speed of light is known and constant, the teeth of the comb can be used like a ruler to measure light emitted or reflected by objects for various purposes. A promising new application for the combs is powering “optical clocks” for GPS satellites that could potentially pinpoint a cellphone user’s location down to the centimeter or even help better detect gravitational waves. GPS works by tracking the time it takes a signal to travel from a satellite to the user’s phone. Other applications include high-precision spectroscopy, enabled by stable optical combs combining different portions of the optical spectrum into one beam, to study the optical signatures of atoms, ions, and other particles.

In these applications and others, it’s helpful to have filters that cover broad, and vastly different, portions of the optical spectrum on one device.

“Once we have really precise clocks with sharp optical and radio-frequency signals, you can get more accurate positioning and navigation, better receptor quality, and, with spectroscopy, get access to phenomena you couldn’t measure before,” Magden says.

The new device could be useful, for instance, for sharper signals in fiber-to-the-home installations, which connect optical fiber from a central point directly to homes and buildings, says Wim Bogaerts, a professor of silicon photonics at Ghent University. “I like the concept, because it should be very flexible in terms of design,” he says. “It looks like an interesting combination of ‘dispersion engineering’ [a technique for controlling light based on wavelength] and an adiabatic coupler [a tool that splits light between waveguides] to make separation filter for high and low wavelengths.”

Boeing will be Kendall Square Initiative’s first major tenant

Wed, 08/01/2018 - 12:59am

Boeing, the world’s largest aerospace company, will soon become part of the MIT/Kendall Square innovation fabric. The company has agreed to lease approximately 100,000 square feet at MIT’s building to be developed at 314 Main St., in the heart of Kendall Square in Cambridge.

The agreement makes Boeing the first major tenant to commit to MIT’s Kendall Square Initiative, which includes six sites slated for housing, retail, research and development, office, academic, and open space uses. The building at 314 Main St. (“Site 5” on the map above) is located between the MBTA Red Line station and the Kendall Hotel. Boeing is expected to occupy its new space by the end of 2020.

“Our focus on advancing the Kendall Square innovation ecosystem includes a deep and historic understanding of what we call the ‘power of proximity’ to address pressing global challenges,” MIT Executive Vice President and Treasurer Israel Ruiz says. “MIT’s president, L. Rafael Reif, has made clear his objective of reducing the time it takes to move ideas from the classroom and lab out to the market. The power of proximity is a dynamic that propels this concept forward: Just as pharmaceutical, biotech, and tech sector scientists in Kendall Square work closely with their nearby MIT colleagues, Boeing and MIT researchers will be able to strengthen their collaborative ties to further chart the course of the aerospace industry.”

Boeing was founded in 1916 — the same year that MIT moved to Cambridge — and marked its recent centennial in a spirit similar to the Institute’s 100-year celebration in 2016, with special events, community activities, and commemorations. That period also represents a century-long research relationship between Boeing and MIT that has helped to advance the global aerospace industry.

Some of Boeing’s founding leaders, as well as engineers, executives, Boeing Technical Fellows, and student interns, are MIT alumni.

Earlier this year, Boeing announced that it will serve as the lead donor for MIT’s $18 million project to replace its 80-year-old Wright Brothers Wind Tunnel. This pledge will help to create, at MIT, the world’s most advanced academic wind tunnel.

In 2017, Boeing acquired MIT spinout Aurora Flight Sciences, which develops advanced aerospace platforms and autonomous systems. Its primary research and development center is located at 90 Broadway in Kendall Square. In the new facility at 314 Main St., Boeing will establish the Aerospace and Autonomy Center, which will focus on advancing enabling technologies for autonomous aircraft.

“Boeing is leading the development of new autonomous vehicles and future transportation systems that will bring flight closer to home,” says Greg Hyslop, Boeing chief technology officer. “By investing in this new research facility, we are creating a hub where our engineers can collaborate with other Boeing engineers and research partners around the world and leverage the Cambridge innovation ecosystem.”

“It’s fitting that Boeing will join the Kendall/MIT innovation family,” MIT Provost Martin Schmidt says. “Our research interests have been intertwined for over 100 years, and we’ve worked together to advance world-changing aerospace technologies and systems. MIT’s Department of Aeronautics and Astronautics is the oldest program of its kind in the United States, and excels at its mission of developing new air transportation concepts, autonomous systems, and small satellites through an intensive focus on cutting-edge education and research. Boeing’s presence will create an unprecedented opportunity for new synergies in this industry.”

The current appearance of the 314 Main St. site belies its future active presence in Kendall Square. The building’s foundation and basement level — which will house loading infrastructure, storage and mechanical space, and bicycle parking — is currently in construction. Adjacent to those functions is an underground parking garage, a network of newly placed utilities, and water and sewer infrastructure. Vertical construction of the building should begin in September.

At 250 feet high, the new 17-floor building will accommodate additional commercial tenants, as well as the MIT Museum, which will occupy over 57,000 square feet on the building’s ground, second, and third floors. The ground floor is designed to feature retail and restaurant uses, including the entrance to the new home for the MIT Press Bookstore.

“Boeing will be a great addition to the Kendall Square innovation ecosystem, “ says Steve Marsh, managing director of MIT’s real estate group. “Boeing has chosen to locate at the new gateway to MIT’s campus being developed above the Kendall MBTA station. This is as close to MIT’s campus as industry innovators can physically get, and that helps promote important collaborations.”

On the other side of the MBTA station, MIT’s new graduate residence hall (“Site 4” on the map above) is already going up. The Institute decided to lead with that 450-unit facility in response to community interest in expanding on-campus housing inventory for graduate students. That building will also serve to shape the East Campus gateway by creating new homes for MIT’s Admissions Office, an innovation and entrepreneurship hub, a childcare center, active retail concepts, and the MIT Forum, which will provide shared space for community programming.

Tying these buildings together will be an outdoor space well over two acres. The area will feature a combination of hard and soft landscape treatments accompanied by art installations, interactive science experiments, inventions, and other engaging and surprising elements showcasing MIT’s innovative and welcoming spirit. The Institute has recently hired Jessie Schlosser Smith as its new director of open space programming; she is already beginning to collaborate with faculty, students, staff, and members of the Cambridge community to envision memorable programming for the outdoor spaces.

Inventing future fabrics

Tue, 07/31/2018 - 12:45pm

A T-shirt that can change color to complement your mood (and help you pare down your wardrobe). An apron that transforms into a dress and has interchangeable pockets with high-tech functionality. These are the forward-looking concepts presented by a group of three students from MIT and three students from the Fashion Institute of Technology (FIT), making practical use of the latest active textile technologies.

For the first FIT/MIT Summer Workshop, held over two weeks in June, the six students spent one week at MIT in Cambridge, Massachusetts and one week at FIT in New York City to explore and develop clothing concepts using advanced functional materials that incorporate 3-D printing or advanced knitting technologies. The workshop was held collaboratively with Advanced Functional Fabrics of America (AFFOA), a Cambridge-based national nonprofit enabling a manufacturing-based transformation of traditional fibers, yarns, and textiles into highly sophisticated integrated and networked devices and systems.

Personal identity

Veronica Apsan, of Park Ridge, New Jersey, a 2018 FIT graduate who majored in fashion design, and Erika Anderson of Carlsbad, California, a rising MIT senior who is studying mechanical engineering with a minor in design, conceived a T-shirt that can change color.

“We were really interested in color and how it affects people’s moods and how they feel,” said Anderson. “Color and clothing are part of a person’s identity and how they want to portray that to the world.” Anderson and Apsan started with a color-changing filament that they 3D-printed into modular components. From there, they moved on to hollow fibers that can be filled with an ink that changes color when an electrical current is sent through it.

“Many people own basic clothing or similar shirts and pants in different colors,” Anderson explained. “This takes up a lot of closet space and costs a lot of money.” A large wardrobe is also not environmentally friendly. With a T-shirt that can change color, a person could radically pare down how many garments they buy and throw out.

The four other students in the workshop combined their ideas into a single wearable concept. David Merchan, of Bow, New Hampshire, a rising MIT senior double majoring in materials science and engineering and physics; Melanie Wong of Queens, New York, a rising senior at FIT majoring in fashion design; Calvin Zhong '18, of Manhattan, a recent MIT graduate who double majored in architecture and comparative media studies; and Jesse Doherty, an FIT rising senior majoring in fashion design, created a double-layer knit laboratory apron with reflective zippers that transforms into a dress or bag and has interchangeable pockets with customizable technological functions. For example, one pocket could have an energy socket that wirelessly charges a phone, while another could act as a hand sanitizer by working into the fiber antimicrobial chemicals or ultraviolet LEDs. The apron/dress itself could also be infused with conductive fibers that cool or warm the wearer.

“You could imagine that a lab tech would have different needs than a doctor, who would have different needs than a DIY hobbyist or a shop manager,” explained Zhong.

3-D-printed mesh

Using 3-D printing, the students knit an open, fully twistable weave mesh for their apron/dress. Once the soluble supports were removed in a chemical bath, the mesh moved in every direction because of the flexible fiber. “The same structure in different materials would behave differently,” noted Doherty.

In addition to conceiving their projects, the students had a packed schedule of workshops, talks, and site visits. While at MIT, they learned about bringing their ideas to market through an intensive entrepreneurship boot camp. They also attended an AFFOA member networking event at the Institute of Contemporary Art in Boston, where Apsan said she and Anderson received positive feedback about their ideas. “The fact that someone in the industry who is working on textiles is thinking the same thing was so awesome to hear,” she said. During their week at FIT, the students visited WGSN, a leading fashion trend, forecast, and analysis service, and met with Gabi Asfour, founder and creative director at threeASFOUR, a clothing design brand, about incorporating 3-D-printed parts into garments. MIT and FIT faculty mentors assisted the students throughout the two weeks.

“We believe this is the future, so we want you all to be involved and help make it happen,” AFFOA Chief Executive Officer Yoel Fink told the group.

Inspiring collaboration

Gregory C. Rutledge, lead principal investigator for MIT in AFFOA and the Lammot du Pont Professor in Chemical Engineering, commented, "It is exciting to see what happens when students from different fields of engineering and design, but with a common interest in advanced fibers and fabrics, come together and engage with new kinds of materials and manufacturing techniques. The collaboration and creativity is inspiring.”

“Combining the talents and skills of FIT and MIT is truly the future,” said Apsan as the two-week workshop wrapped up.

“This workshop validates the benefits of bringing FIT and MIT students together. For this specific workshop, the students explored the possibilities of advanced knitting and 3-D printing,” said Joanne Arbuckle, deputy to the president for industry partnerships and collaborative programs at FIT. “As the fashion industry becomes more and more dependent on advanced textiles, students who have the experience this workshop has provided will prove to be the industry’s next leaders.”

Featured video: If the spacesuit fits

Tue, 07/31/2018 - 11:25am

Movement really moves Richard Fineman, a fourth-year PhD student in the Harvard-MIT Program in Health Sciences and Technology. Using wearable sensors and a range of complex modeling tools, Fineman is able to measure and understand a body in motion in unprecedented ways. He is using what he’s learning to advance human health and medicine, as well as astronaut garb.

As a lifelong athlete, Fineman has always been interested in biomechanics and human motion. In his work, he is “able to evaluate whether a patient is at risk for falling” by using cameras and computers to gather position and movement data. Subjects in the lab are fitted with wearable sensors and asked to complete certain tasks. Their movements are tracked and captured and the resulting data is processed and analyzed to help define models that can “determine whether or not someone is at high versus low fall risk,” he explains.

Fineman’s work measuring movement here on Earth piqued his curiosity about human bodies in motion in other environments. “How does human motion change in altered gravity environments?” he asks. “I think about how spacesuits are these big bulky objects. … Each suit has to be fit to the human, but we don’t really have objective ways to determine how well the suit fits.”

Luckily, Fineman is a member of Assistant Professor Leia Stirling's group in the Department of Aeronautics and Astronautics, where he was able to step into a space suit himself to experiment. Using his wearable sensors, Fineman was able to come up with techniques to evaluate and improve the way the space suit fits on the human.

Submitted by: Carolyn Blais | Video by: Lillie Paquette | 2 min, 11 sec

Abdul Latif Jameel World Education Lab welcomes initial members

Tue, 07/31/2018 - 11:00am

In its first year, the Abdul Latif Jameel World Education Lab (J-WEL) has welcomed a diverse group of organizations as members, including leading universities, major non-governmental organizations (NGOs), and top companies. J-WEL, launched in May of last year, promotes excellence and transformation in global education across the lifespan of the learner, through collaboratives at the pK-12, higher education, and workplace learning levels.

The pK-12 Collaborative, under the direction of professors Angela Belcher and Eric Klopfer, has a growing list of members including the Hong Kong-based nonprofit Catalyst Education Lab, Save the Children, educational technology company EnglishHelper (United States), Australia’s Queensland University of Technology (QUT), and the Wadah Foundation (Indonesia).

The Higher Education Collaborative, led by faculty director Professor Hazel Sive, has been joined by members from Africa, Asia, Latin America, and the Caribbean. These include Ahmadu Bello University (Nigeria), Covenant University (Nigeria), Seikei University (Japan), Universidad de los Andes (Colombia), Universidad Mayor (Chile), University of São Paulo (Brazil), and the University of The Bahamas.

Members joining the Workplace Learning Collaborative, which is led by MIT Sloan School of Management Principal Research Scientist George Westerman, include Intelligent Machines Lab and UBS.

“The high caliber of the organizations that have joined J-WEL, and the speed with which they have come on board, is testament to the impact that J-WEL has made in such a short space of time,” says Fady Jameel, president of Community Jameel International, the social enterprise organization that co-founded J-WEL with MIT in 2017. “The different members will bring wide-ranging insights to the table at the pulsating meetings of J-WEL Weeks and other events — but they are unified by their commitment to discovering and sharing innovative approaches to learning, and applying them in the real world.”

J-WEL promotes excellence and transformation in education at MIT and globally by engaging with educators, technologists, policymakers, societal leaders, employers, and employees. Through online and in-person collaborations, workshops, research, and information-sharing events, J-WEL member organizations work with MIT faculty and staff to address global opportunities for scalable change in education. J-WEL shares MIT’s “mens et manus” (“mind and hand”) approach, entrepreneurial spirit, and insights into digital learning, artificial intelligence, learning sciences, and other fields that are disrupting the education and training landscape as well as offering new opportunities to transform teaching and learning.

“Each collaborative is taking a unique approach to engaging with its members to define and explore educational challenges and opportunities that can have global impact,” says M.S. Vijay Kumar, associate dean for digital learning and J-WEL’s executive director, in discussing J-WEL’s first year. “We’re thrilled to have this remarkable group of organizations working with us.”

Professor Sylvio Canuto, University of São Paulo’s research provost and membership coordinator, describes his university’s motivation for involvement: “USP has joined J-WEL due to MIT's long history of excellence and due to the great opportunities that arise from being part of a global program that aims to tackle the great challenge of enhancing education.”

J-WEL supports educational research and innovation by MIT faculty and staff through grants and collaborative projects with J-WEL members. J-WEL engages MIT students through volunteer opportunities at J-WEL events and through the J-WEL Global Ambassadors program, which offers MIT students the opportunity to work on meaningful education projects across the globe.

J-WEL is an initiative of MIT and Community Jameel, the social enterprise organization founded by MIT alumnus Mohammed Jameel '78. Community Jameel was established in 2003 to continue the Jameel family's tradition of supporting the community, a tradition started in the 1940s by the late Abdul Latif Jameel, founder of the Abdul Latif Jameel business, who throughout his life helped tens of thousands of disadvantaged people in the fields of health care, education, and improving livelihoods. Today, Community Jameel is dedicated to supporting social and economic sustainability across the Middle East and beyond through a range of initiatives including J-WEL and two other labs at MIT: the Abdul Latif Jameel Poverty Action Lab (J-PAL) and the Abdul Latif Jameel World Water and Food Security Lab (J-WAFS).

China could face deadly heat waves due to climate change

Tue, 07/31/2018 - 10:59am

A region that holds one of the biggest concentrations of people on Earth could be pushing against the boundaries of habitability by the latter part of this century, a new study shows.

Research has shown that beyond a certain threshold of temperature and humidity, a person cannot survive unprotected in the open for extended periods — as, for example, farmers must do. Now, a new MIT study shows that unless drastic measures are taken to limit climate-changing emissions, China’s most populous and agriculturally important region could face such deadly conditions repeatedly, suffering the most damaging heat effects, at least as far as human life is concerned, of any place on the planet.

The study shows that the risk of deadly heat waves is significantly increased because of intensive irrigation in this relatively dry but highly fertile region, known as the North China Plain — a region whose role in that country is comparable to that of the Midwest in the U.S. That increased vulnerability to heat arises because the irrigation exposes more water to evaporation, leading to higher humidity in the air than would otherwise be present and exacerbating the physiological stresses of the temperature.

The new findings, by Elfatih Eltahir at MIT and Suchul Kang at the Singapore-MIT Alliance for Research and Technology, are reported in the journal Nature Communications. The study is the third in a set; the previous two projected increases of deadly heat waves in the Persian Gulf area and in South Asia. While the earlier studies found serious looming risks, the new findings show that the North China Plain, or NCP, faces the greatest risks to human life from rising temperatures, of any location on Earth.

“The response is significantly larger than the corresponsing response in the other two regions,” says Eltahir, who is the the Breene M. Kerr Professor of Hydrology and Climate and Professor of Civil and Environmental Engineering. The three regions the researchers studied were picked because past records indicate that combined temperature and humidity levels reached greater extremes there than on any other land masses. Although some risk factors are clear — low-lying valleys and proximity to warm seas or oceans — “we don’t have a general quantitative theory through which we could have predicted” the location of these global hotspots, he explains. When looking empirically at past climate data, “Asia is what stands out,” he says.

Although the Persian Gulf study found some even greater temperature extremes, those were confined to the area over the water of the Gulf itself, not over the land. In the case of the North China Plain, “This is where people live,” Eltahir says.

The key index for determining survivability in hot weather, Eltahir explains, involves the combination of heat and humidity, as determined by a measurement called the wet-bulb temperature. It is measured by literally wrapping wet cloth around the bulb (or sensor) of a thermometer, so that evaporation of the water can cool the bulb. At 100 percent humidity, with no evaporation possible, the wet-bulb temperature equals the actual temperature.

This measurement reflects the effect of temperature extremes on a person in the open, which depends on the body’s ability to shed heat through the evaporation of sweat from the skin. At a wet-bulb temperature of 35 degrees Celsius (95 F), a healthy person may not be able to survive outdoors for more than six hours, research has shown. The new study shows that under business-as-usual scenarios for greenhouse gas emissions, that threshold will be reached several times in the NCP region between 2070 and 2100.

“This spot is just going to be the hottest spot for deadly heat waves in the future, especially under climate change,” Eltahir says. And signs of that future have already begun: There has been a substantial increase in extreme heat waves in the NCP already in the last 50 years, the study shows. Warming in this region over that period has been nearly double the global average — 0.24 degrees Celsius per decade versus 0.13. In 2013, extreme heat waves in the region persisted for up to 50 days, and maximum temperatures topped 38 C in places. Major heat waves occurred in 2006 and 2013, breaking records. Shanghai, East China’s largest city, broke a 141-year temperature record in 2013, and dozens died.

To arrive at their projections, Eltahir and Kang ran detailed climate model simulations of the NCP area — which covers about 4,000 square kilometers — for the past 30 years. They then selected only the models that did the best job of matching the actual observed conditions of the past period, and used those models to project the future climate over 30 years at the end of this century. They used two different future scenarios: business as usual, with no new efforts to reduce emissions; and moderate reductions in emissions, using standard scenarios developed by the Intergovernmental Panel on Climate Change. Each version was run two different ways: one including the effects of irrigation, and one with no irrigation.

One of the surprising findings was the significant contribution by irrigation to the problem — on average, adding about a half-degree Celsius to the overall warming in the region that would occur otherwise. That’s because, even though extra moisture in the air produces some local cooling effect at ground level, this is more than offset by the added physiological stress imposed by the higher humidity, and by the fact that extra water vapor — itself a powerful greenhouse gas — contributes to an overall warming of the air mass.

“Irrigation exacerbates the impact of climate change,” Eltahir says. In fact, the researchers report, the combined effect, as projected by the models, is a bit greater the sum of the individual impacts of irrigation or climate change alone, for reasons that will require further research.

The bottom line, as the researchers write in the paper, is the importance of reducing greenhouse gas emissions in order to reduce the likelihood of such extreme conditions. They conclude, “China is currently the largest contributor to the emissions of greenhouse gases, with potentially serious implications to its own population: Continuation of the current pattern of global emissions may limit habitability of the most populous region of the most populous country on Earth.”