The war against malaria has a new ally: a controversial technology for spreading genes throughout a population of animals. In the laboratory, researchers have harnessed a so-called gene drive to efficiently endow mosquitoes with genes that make them immune to the malaria parasite—and unable to spread it. If successfully applied in the wild, the approach could help wipe out the disease, at least in some corners of the world. But testing that promise in the field may have to wait until a wider debate over gene drives is resolved. A firestorm has erupted over the risks of experimenting with gene drives, nevermind applying them in the field, and there is a strong push to get the public involved in regulating this technology early on in the development of specific gene drive uses. Author: Elizabeth Pennisi

China's main basic research agency is cracking down on scientists who used fake peer reviews to publish papers in international journals, demanding that many return research funding. A separate Chinese scientific organization released the results of an investigation revealing the role of China's many unscrupulous paper brokers, which peddle ghostwritten or fraudulent papers, in the peer-review scandal. In some cases brokers suggested reviewers for their clients' papers, provided email addresses to accounts they controlled, and then reviewed the authors' work themselves. The National Natural Science Foundation is now revoking funding from authors found to have committed egregious offenses. But critics say the measures don't go far enough to stave off fraud. Author: Mara Hvistendahl

Hope and caution surround the upcoming Paris climate talks. More than 2 decades have passed since nations met in Rio de Janeiro, Brazil, to create the 1992 United Nations Framework Convention on Climate Change. Since then, a succession of international meetings under the framework—most notably in Kyoto, Japan, in 1997 and Copenhagen in 2009—have done little to alter our planet's worrisome trajectory. Annual global emissions of carbon dioxide have risen steadily from 21 billion tons in 1992 to 32 billion tons in 2012. And the dismal track record of global climate talks inspires little confidence that nations can agree to make the huge changes required to stop treating the atmosphere like a carbon sewer. Still, negotiators are convinced the Paris talks will be different. In Kyoto, nations attempted to create a legally binding agreement, which subsequently failed to deliver results in part because the United States would not ratify the treaty. This time, nations—164 as Science went to press—have each prepared pledges, called Intended Nationally Determined Contributions (INDCs), which detail their promised emissions cuts and other actions through 2030. Negotiators hope the bottom-up INDC approach will prevail where the top-down Kyoto strategy failed. Author: Eli Kintisch

Officials call the Paris climate talks a beginning, but what's the destination? In a series of informational graphics, Science explores the implications of three possible scenarios for global greenhouse gas emissions until 2100. One is a "business as usual" scenario that results in massive warming by the end of the century, and then many meters of sea level rise that would unfold over centuries. Another is a scenario that assumes nations meet the pledges they make in Paris, causing global emissions to dip, but then take no further action, causing emissions to rise again as population and economic growth swamp any gains. The final scenario explores what it will take to hold global warming below the 2°C of warming many researchers deem safe. For each scenario, graphics illustrate the possible range of outcomes for sea level rise, warming, and atmospheric concentrations of carbon dioxide, and provide insight to choices about energy sources that will shape future emissions. Author: Eli Kintisch

Denmark—a small, resource-poor country of 5.5 million people—has set the most ambitious climate goal in the world: to become a carbon neutral economy by 2050. And as delegates gather in Paris to hammer out a global agreement to slow climate change, many are looking to Denmark to understand how their nations might also rapidly transform their energy systems. "The Denmark model is really important," says Dan Kammen, an energy policy expert at the University of California, Berkeley. "It's an illustration of what can be done." But Denmark is also helping highlight the potential technical and political obstacles to going green. The nation has struggled to align its bold emissions goal with tax and economic policies, and some aspects of the carbon neutral push have become politically contentious. The experience, says Lars Aagaard, managing director of the Danish Energy Association in Copenhagen, "is certainly not a walk in the park." Author: Robert F. Service

India, a nation with Earth's third largest coal reserves, has been on course to eventually vie with China as the world's top greenhouse gas emitter. And it has long resisted calls to cap its future emissions, arguing that it has not historically contributed much to climate change, and will need "carbon space" in the future to grow its economy and lift hundreds of millions of people from poverty. At the Paris talks, however, India has pledged to take steps that would keep its per capita emissions well below China's for the foreseeable future. Those steps include deriving 40% of electric power capacity from fossil fuel–free sources by 2030, reducing its emissions intensity by 33% to 35% by 2030, and expanding forests to create a carbon sink capable of absorbing 2.5 billion to 3 billion tons of carbon from the atmosphere. But analysts say some of these goals will be a stretch to achieve, and they also have helped spark a domestic debate over how these goals will improve life for India's citizens. Indeed, some critics argue that some of India's climate commitments could actually threaten equity, inclusiveness, and quality of life. Author: Priyanka Pulla

Game-changing moments in functional genomics often reflect the development and application of powerful new reagents and methods to provide new phenotypic insight on a global scale. Three independent studies describe systematic, genome-scale approaches to defining human genes that are indispensable for viability, which collectively form the essential gene set. On pages 1092 and 1096 of this issue, Blomen et al. (1) and Wang et al. (2), respectively, report a consistent set of ∼2000 genes that are indispensable for viability in human cells. Moreover, very similar results were obtained by Hart et al. (3). For the first time, we now have a firm handle on the core set of essential genes that are required for human cell division. This opens the door to studying the roles of essential genes, how gene essentiality depends on genetic and tissue contexts, and how essential genes evolve. Authors: Charles Boone, Brenda J. Andrews

It is appealing to harvest solar energy directly into chemical bonds with photo-electrochemical (PEC) cells—for example, by splitting water into hydrogen (H2) and oxygen (O2), as first demonstrated by Fujishima and Honda (1). Achieving the highest possible efficiency requires rapid transfer of the charge carriers generated by semiconductor photoabsorbers (2) to the catalysts for H2 and O2 evolution. Long-term stability requires protection layers for the semiconductors against strong acid or base. Direct experimental observation of charge carrier dynamics at these complex interfaces, which is critical for optimization, has been a major challenge. On page 1061 of this issue, Y. Yang et al. (3) show how transient photoreflectance spectroscopy can reveal information about the carrier dynamics and the electric field near the semiconductor surface. Authors: Ole Hansen, Brian Seger, Peter C. K. Vesborg, Ib Chorkendorff

Immunotherapies known as checkpoint blockades are rapidly changing standard treatment and outcomes for patients with advanced malignancies, as they lead to long-term disease control in a subset of patients (1). On pages 1084 and 1079 of this issue, Sivan et al. (2) and Vétizou et al. (3), respectively, illustrate an important role for the gut microbiome in modulating the efficacy of this treatment. Authors: Alexandra Snyder, Eric Pamer, Jedd Wolchok

Nonlinear optics investigates the light-matter interactions in media, in which the dielectric polarization of the medium responds nonlinearly to the electric and/or magnetic field of the light. Materials with the potential for a large, fast, and broadband nonlinear response have been explored for decades; if realized, these would revolutionize nonlinear optics, leading to low-power, compact, and ultrafast applications. However, the materials now available are limited, either by relatively low nonlinear susceptibilities for ultrafast nonlinear processes or by slow response times attributable to photorefractive effect and thermal nonlinear phenomena. Moreover, growing demand for integration of multiple optoelectronic functionalities on a chip calls for nonlinear materials that are compatible with standard fabrication approaches, such as complementary metal-oxide semiconductor technology. Metamaterials have been predicted to enable a plethora of novel light-matter interactions, including magnetic nonlinear response, backward phase-matching, and the nonlinear mirror (1–3). Linear optical properties such as dielectric permittivity, magnetic permeability, and refractive index can be designed to be positive, negative, or even zero by properly tailoring various properties of meta-atoms (the unit cells of metamaterials). Engineering nonlinear properties of metamaterials beyond those available in nature may be feasible by judiciously designing their quantum, geometric, and topological properties (4). Authors: Natalia M. Litchinitser, Jingbo Sun

More than 130 countries have targets for increasing their share of renewable or nonfossil energy (1). These shares and targets are often reported without clear articulation of which energy accounting method was used to convert nonfossil electricity into units that allow comparison with other energy sources (2–4). Three commonly used conversion methods are well documented by organizations dealing in energy statistics, but often, the method is not clearly stated when countries translate national targets into international pledges or when organizations track and compare targets across nations. China—the world's largest energy producer, energy consumer, and emitter of energy-related carbon dioxide (CO2)—uses a distinct fourth method that is unique, not well documented in the literature, and not transparent in policy documents. A single, standardized, and transparent methodology for any targets that are pledged as part of an international agreement is essential. Authors: Joanna I. Lewis, David G. Fridley, Lynn K. Price, Hongyou Lu, John P. Romankiewicz

Earth's animals are downsizing. Since the end of the last ice age about 12,000 years ago, the largest animals on the planet have been hit disproportionately hard by what may have been the beginnings of the sixth mass extinction (1). We are only just beginning to appreciate the ecological impacts of this “trophic downgrading” (2): Both modern and paleoecological analyses are providing growing evidence that the extinction of Earth's largest animals has cascading ecological impacts across the globe (3). On page 1056 of this issue, Hempson et al. (4) provide a new tool for elucidating the ecological role of large herbivores at continental scales. Author: Jacquelyn L. Gill

Intuition can be a powerful force in science, but more often proves to be an unreliable guide to reality. This point is beautifully brought home in the report by McGee et al. (1) on page 1077 of this issue. The study concerns evolutionary innovations that enable members of an evolving lineage to exploit resources in ways inaccessible to their ancestors. Most biologists view such innovations as opening the evolutionary door to species proliferation and the longer persistence of lineages with the novel traits. This expectation is often realized. But, as McGee et al. show in their study of cichlid fishes in East Africa's Lake Victoria, this is not always the case. Author: Geerat Vermeij

Alan Hall, a remarkable cell and cancer biologist, died suddenly on 3 May in New York City. He was an outstanding researcher, teacher, and colleague. In the 1980s, in his early career, Alan was one of a small group of molecular biologists who first revealed how genetic changes could cause cancer. Alan and his colleagues undertook pioneering work that revealed the mechanisms through which the Rho family of small guanosine triphosphatases (GTPases) regulate the cytoskeleton and thus how cells control their shapes and movement. He became one of the world's leading cell biologists and was a committed mentor to generations of young scientists. Authors: Catherine Nobes, Alison Lloyd, Mark Marsh

Christopher Marshall was a titan of cancer research. On 8 August he died of the very disease that he strived to understand. This was only 3 months after the unexpected death of his longtime friend and colleague, Alan Hall. Author: Richard Marais

HUMAN+, a new, ambitious, and sharply curated exhibition at the Centre for Contemporary Culture in Barcelona, delves into the contemporary meaning of being human. Hosting more than 50 works created by artists and scientists, the collection explores the technological strategies that we might use to transcend bodily and mental limits, our place in nature, and our social interactions, as well as redefinitions of birth and death. In this review, Giovanni Frazzetto highlights some of the exhibition's challenging and provocative exhibits. Author: Giovanni Frazzetto

Database of Dreams tells the story of the enormous effort and expense that went into creating a once popular, but now long-forgotten archive of social science data. Tracing the archive's origins and evolution, reviewer Laura Stark describes how the archive's greatest virtue was also, ultimately, it's fatal flaw. Praising the book as "humane, hilarious, and smart," Stark distills lessons that are relevant to many of today's "big data" initiatives. Author: Laura Stark

In Thing Explainer, xkcd creator Randall Munroe sets out to demystify a wide range of complex systems and natural phenomena using only the thousand most common words in the English language.

A listing of books received at Science during the week ending 20 November 2015.

Authors: Hudson T. Pinheiro, Fabio Di Dario, Leopoldo C. Gerhardinger, Marcelo R. S. de Melo, Rodrigo L. de Moura, Roberto E. Reis, Fábio Vieira, Jansen Zuanon, Luiz A. Rocha