Over the past decade, pioneering developments of visible-light photocatalysis in organic synthesis have enabled previously inaccessible redox-neutral reactions that proceed through single-electron transfer (SET) processes (1, 2). Nonetheless, the use of photocatalysts, mostly precious metal complexes (3) or sophisticated organic dyes (4), could have practical limitations, such as the nontrivial tuning of redox potentials; high cost of transition-metal photocatalysts at scale (5); incompatibility of photocatalysts with strong nucleophiles, electrophiles, or radical intermediates (6, 7); and challenging removal of transition metals during purification of the products (8, 9). Electrosynthesis, on the other hand, is an emerging redox platform accessing environmentally benign, cost-effective, scalable, and distinctive transformations (10) powered by inexpensive electricity. Consequently, we considered whether electrochemistry could be applied in a practical photocatalyst-free system for SET redox-neutral reactions.

Most of the reported synthetic electrochemistry relies on reactions on a single electrode with by-products generated on the other electrode, and, as such, the nature of the desired electrochemical transformations is either oxidative or reductive (10). In contrast, redox-neutral electrochemistry (i.e., paired or coupled electrosynthesis), which involves two desirable half-electrode reactions performed simultaneously, is underdeveloped, despite its relative material and energy efficiency (10–12), and examples of radical-based redox-neutral electrosynthesis are even rarer (13–15). In conventional paired electrochemistry setups, the difficulties associated with matching the generation and interelectrode transport rates of the different highly reactive intermediates pose substantial obstacles to achieving the selective transformation over alternative undesired pathways. Microfluidics, however, has been shown to offer controllable and rapid species transport within a micrometer channel (16), with recent applications in electrosynthesis for improved reaction performance (17, 18). To further exploit the capability of microfluidic electrochemistry, we sought to develop a microfluidic redox-neutral electrochemical (?RN-eChem) platform to overcome the challenges of photochemistry-inspired SET redox-neutral reactions that involve reactive intermediates generated from both electrodes.

Fig. 1 Background and microfluidic redox-neutral electrochemistry (?RN-eChem).

(A) Comparison of photochemistry and electrochemistry for SET redox-neutral reactions. PC, photocatalyst; PCRed, ground-state PC; PC*Red, excited-state PC; PCOx, oxidized-state PC. (B) Concept of ?RN-eChem for the cross-coupling reaction of persistent and transient radicals. (C) Mechanism of redox-neutral electrochemical cross-coupling reaction of carboxylic acids and electron-deficient aryl nitriles. R–COOH, carboxylic acid (where R is the alkyl group); R•, alkyl radical; EWG, electron-withdrawing group. (D) UV-Vis spectroelectrochemical lifetime measurement of BPDN radical anion. a.u., arbitrary units; Decomp., decomposition; [C], concentration; ?, wavelength. (E) Effect of interelectrode distance on reaction yield. Two batch setups were tested (fig. S5), and the setup with higher yield is presented in this plot. Me, methyl.

We engineered a ?RN-eChem flow cell with a variable interelectrode distance (25 to 500 ?m). Two GC plate electrodes, micromachined by a 532-nm laser, sandwich a thin fluorinated ethylene propylene film to create the microfluidic channel (see fig. S1)

Glassy carbon electrodes (50 mm × 50 mm × 3 mm) were purchased from Alfa Aesar (P.N. 42820-FI) without further treatment. (Note: only type 1 glassy carbon electrode works for chemistry developed in this work, and type 2 glassy carbon electrode shows unstable electrode surface properties under our electrochemical conditions.) Fluorinated ethylene propylene (FEP) spacers with various thickness (0.001” – 0.005”) were obtained from CS Hyde Company. PTFE and PFA films were also tested for flow cell sealing. However, FEP film proved to be the best for sealing the thin gap between glassy carbon electrodes (no leakage tested up to 40 psig of nitrogen gas).

Fabricating a small diameter and high aspect ratio deep hole in glassy carbon is challenging using the traditional milling process. Here, we used the laser micromachining process to microfabricate these fluid paths. In this process, the laser was used to oxidize the glassy carbon into carbon dioxide in the presence of atmospheric oxygen. The resulted carbon dioxide gas escaped to the environment, giving the efficient removal of glassy carbon. Deep holes were obtained by gradually moving the focus of the laser beam and removing the material layer-by-layer until the desired depth was achieved. A laser micromachining system from Oxford Lasers was used for drilling the holes. The laser source in the system was a Q-switched frequency-doubled Nd:YAG diode-pumped solid-state pulsed laser with a wavelength of 532 nm and a pulse duration of 20 ns. The laser was focused using a 100 mm focal length lens giving a spot size of 10 micrometers. For drilling holes, the average laser power of 1.4 W was used.

Fig. 2 Substrate scope of decarboxylative arylation in continuous-flow synthesis enabled by ?RN-eChem.
See the supplementary materials for detailed reaction conditions for each substrate; reactions were performed on a 0.4-mmol scale, unless otherwise noted. Asterisks indicate isomers observed, and in all cases the major isomer is depicted. Yields refer to the combined yield of all isomers. Boc, tert-butyloxycarbonyl; t-Bu, tert-butyl; Et, ethyl; rr, regioisomeric ratio.

Fig. 3 General applicability of ?RN-eChem platform for SET redox-neutral chemistry.

(A) ?-Amino C–H arylation. (B) Deboronative arylation. (C) Thiol-catalyzed allylic C–H arylation. HAT, hydrogen atom transfer; i-Pr, isopropyl. (D) Minisci-type radical addition to heteroarenes. Mediators (Med) used are ferrocene or 4-methoxytriphenylamine. Ts, tosyl; DMSO, dimethyl sulfoxide; NHP, phthalimide. (E) Ni-catalyzed C–O cross-coupling. dtbbpy, 4,4?-di-tert-butyl-2,2?-dipyridyl. Asterisks indicate high-performance liquid chromatography yield obtained from batch setup (fig. S5B) under identical electrochemistry conditions. See the supplementary materials for detailed reaction conditions.

Fig. 4 A fully electrochemical two-step synthesis of liquid crystal material 5CB.

See the supplementary materials for detailed reaction conditions. DMF, N,N?-dimethylformamide; PP, polypropylene.

Terrestrial ecosystems currently absorb ~30% of human carbon emissions each year (1), and forests account for the vast majority of this uptake [an estimated 8.8 Pg CO2e year?1 of a total land carbon uptake of 9.5 Pg CO2e year?1 over 2000–2007, where CO2e denotes CO2 equivalents (2, 3)]. A broad body of literature has focused for decades on the role of forests in the climate system (4–6), and forest-based natural climate solutions (F-NCSs) have experienced growing interest in recent years as a potentially major contributor to meeting Paris Agreement carbon targets (7–10). Forest-based strategies might provide up to 7 Pg CO2e of climate mitigation per year by 2030 at a carbon price of $100 per Mg CO2e, which is by far the largest potential category of natural climate solutions (NCSs) (7). Furthermore, many of these forest-based strategies are likely to have substantial cobenefits for biodiversity, ecosystem services, and conservation (9, 11).

Carbon policy that includes F-NCSs is building around the world (Fig. 1). For example, California has recognized 133 Tg CO2e in benefits from forest carbon offset projects in the United States between 2013 and 2019, with these credits making up a meaningful share of the compliance with the state’s cap-and-trade program (12). National and subnational government policies to reduce emissions have included forest projects, with policies in Japan, Australia, New Zealand, and British Columbia, Canada (Fig. 1). Additionally, many F-NCS projects have occurred under the framework of the United Nations’ Reducing Emissions from Deforestation and Degradation (REDD+) (13, 14) and under local and national emissions reduction goals...

Fundamental questions remain, however, about the fate of carbon stored in forests in a rapidly changing climate, particularly the extent to which climate change and climate-driven changes in disturbance regimes might compromise forest permanence (17–19). Climate-induced tree mortality events have been widely observed across the globe over the past few decades (20, 21). In addition to direct climate impacts on trees like drought events, additional disturbance agents including wildfire and insect outbreaks are sensitive to climate and have major carbon cycle consequences for forests (22–25). The biomass dynamics of an estimated 44% of forests globally are strongly sensitive to stand-replacing disturbance (including harvest) (Fig. 2) (26). Further, climate-driven tree mortality and disturbances are nonstationary (they change with time) and are projected to increase with climate change (25). Finally, due in part to the large uncertainties about climate impacts, CO2 fertilization, and disturbances in forests (27), Earth system model projections over the 21st century indicate that terrestrial ecosystems could sequester as much as 36.7 Pg CO2e year^(?1) or release as much as 22 Pg CO2e year^(?1) by 2100 for a high-emissions scenario (28).

Fire

Fires in forests are perhaps the most well-quantified global disturbance and permanence risk. Between 1997 and 2016, an average of ~500 million ha of land burned each year, most of which is outside of forest ecosystems (36). Although burned area is declining in grasslands and savannas, burned area is increasing in many tropical, temperate, and boreal forest ecosystems (36). Fire in forests emits ~1.8 Pg CO2e year?1 (37, 38). Fire accounts for ~12% of stand-replacing disturbances in forest ecosystems annually (26) and is particularly important in key forest regions like the western United States, Australia, Mediterranean-type climates, and boreal forests in North America and Asia (39, 40). Climate-driven changes in fire regimes can affect permanence both through changes in burned area and through changes in fire behavior (i.e., fire temperature or scorch height) that influence tree mortality...

...Drought

Globally, droughts represent a major and widespread permanence risk, underscored by the explosion of research relating to drought-induced tree mortality that has been done in the past decade (21, 52). Drought events have major impacts on forest carbon cycling through declines in productivity and carbon losses through mortality (20, 27). Major climate extremes explain up to 78% of the variation in global gross primary productivity in the past 30 years, and severe droughts made up ~60 to 90% of the largest extremes (53). As an example, the severe 2011–2015 drought in California killed more than an estimated 140 million trees and drove the full carbon balance of the state’s ecosystems to be a net source of ?600 Tg CO2e from 2001 to 2015, which is equivalent to ~10% of the state’s greenhouse gas emissions over that period (54). A 2011 drought in Texas killed 9.5% of tree cover across the state...

...Biotic agents

Biotic disturbance agents, including insects and pathogens, cause substantial tree mortality globally. For example, bark beetles, which feed on tree phloem and introduce fungi that interrupt tree water transport, have killed billions of trees across millions of hectares of land in temperate and boreal coniferous forests in the past two decades (68–70) and have converted large regions of the Canadian boreal forest from a sink to a source over the course of a decade (34). Defoliators feed on leaves and can kill trees after multiple years of severe damage. Widespread tree mortality has occurred from defoliators in both coniferous and broad-leaved forests in temperate and boreal regions (24, 71). In addition to these native biotic agents, non-native invasive biotic disturbance agents are responsible for killing many trees globally. Prominent examples include Phytophthora-induced sudden oak death and the emerald ash borer in the United States and the red turpentine beetle in China (72)...

...Other disturbances

Other disturbances—particularly storms and wind-driven events, snow and ice events, and lightning—can also influence forest ecosystem carbon cycling (25, 83). These disturbance events can matter for local- to regional-scale carbon cycling in some areas but are thought to have relatively minor-to-modest global effects (25, 53). Hurricanes damage coastal forests and can have pronounced impacts on carbon budgets. For example, Hurricane Katrina damaged 320 million large trees that contained 385 Tg CO2e (83), and tropical cyclones had a net effect of a modest carbon source in the 20th century across U.S. forests (33)...

Fig. 2 Sensitivity of global forest biomass dynamics to stand-replacing disturbance (excluding human land use changes) captured by disturbance return interval (years).

Warm colors indicate areas where biomass dynamics are highly sensitive to the frequency of stand-replacing disturbance and cool colors indicate areas that are relatively less sensitive. Redrawn from (26).

Fig. 4 Climate change has already increased fire risk in ecosystems.

(A and B) Integrated 100-year fire risk of moderate- or high-severity fire from the Monitoring Trends in Burn Severity (MTBS) dataset based on fire occurrences in years 1984–2000 aggregated to ecoregions (A) and for fire occurrences in years 2001–2017 aggregated to ecoregions (B). Fire risk was computed as follows. First, within each ecoregion and year, a pixel-wise burn probability was computed as the fraction of pixels in that ecoregion labeled as moderate or severe fire, and these probabilities were then averaged in each time period. To project an integrated 100-year risk, we computed the probability of any pixel experiencing at least one fire under a binomial distribution with 100 trials and success probability given by the pixel-wise annual risk described above. This is a simple analysis that does not account for spatial or temporal autocorrelation or attempt to model any drivers of fire risk. Raw data obtained from www.mtbs.gov/direct-download, and Python code to create figures is available at https://github.com/carbonplan/forest-climate-risks.

This week, black scientists and recreational birders flocked to Twitter for #BlackBirdersWeek. “Nature is my favorite place to be, & I’ve been fortunate enough [to] use my PhD to travel & be #BlackInNature across the world,” tweeted a graduate student.

The first-of-its-kind event was organized in response to an incident that transpired in New York’s Central Park last week. Christian Cooper—a black man who works as a writer and editor and is an avid birdwatcher—encountered a white woman who was walking her dog while he was birding. When he asked her to leash her dog, she called the police, telling them that an African American man was threatening her. A video of the encounter went viral—unleashing a torrent of discussion about racism and the dangers black people face when they are simply enjoying, or working in, outdoor spaces.

For black scientists in field disciplines such as ecology and geology, Cooper’s experience was a familiar one. Many are sent to remote places to conduct fieldwork—and that can land them in uncomfortable, and potentially dangerous, situations, says Corina Newsome, a master’s student at Georgia Southern University who studies seaside sparrows in coastal marshes. “I’m in these remote, expansive natural areas, and in the South no less, and so my family is … always scared for my safety.”

She and others organized #BlackBirdersWeek to highlight the stories of black people in the outdoors...

...Q: How did you all come up with the idea for #BlackBirdersWeek?

A: The idea came from a group that I’m a part of, which includes probably 100 black people who enjoy the outdoors—either as scientists or outdoor enthusiasts. When the incident happened with Christian in Central Park, one of the members who's actually an economist—she's in mathematics—messaged to say that we need to do something to celebrate black birding. It took off from there; it came together in literally 48 hours. We designed events to highlight the experience of black people, the existence of black people, the work of black people, and to open dialogue.

We were motivated to do that because the incident in Central Park was something that all of us, at some point and in some shape or form, have experienced. But it's never been recognized on such a level...

The ongoing severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) pandemic has caused nearly 500,000 detected cases of coronavirus disease 2019 (COVID-19) illness and claimed >20,000 lives worldwide as of 26 March 2020 (1). Experience from China, Italy, and the United States demonstrates that COVID-19 can overwhelm even the healthcare capacities of well-resourced nations (2–4). With no pharmaceutical treatments available, interventions have focused on contact tracing, quarantine, and social distancing. The required intensity, duration, and urgency of these responses will depend both on how the initial pandemic wave unfolds and on the subsequent transmission dynamics of SARS-CoV-2. During this initial pandemic wave, many countries have adopted social distancing measures and some, like China, are gradually lifting them after achieving adequate control of transmission. However, to mitigate the possibility of resurgences of infection, prolonged or intermittent periods of social distancing may be required. After the initial pandemic wave, SARS-CoV-2 might follow its closest genetic relative, SARS-CoV-1, and be eradicated by intensive public health measures after causing a brief but intense pandemic (5). Increasingly, public health authorities consider this scenario unlikely (6). Alternatively, the transmission of SARS-CoV-2 could resemble that of pandemic influenza by circulating seasonally after causing an initial global wave of infection (7)...

...The pandemic and postpandemic transmission dynamics of SARS-CoV-2 will depend on factors including the degree of seasonal variation in transmission, the duration of immunity, and the degree of cross-immunity between SARS-CoV-2 and other coronaviruses, as well as the intensity and timing of control measures. SARS-CoV-2 belongs to the Betacoronavirus genus, which includes the SARS-CoV-1 coronavirus, the Middle East respiratory syndrome (MERS) coronavirus, and two other HCoVs, HCoV-OC43 and HCoV-HKU1. The SARS-CoV-1 and MERS coronaviruses cause severe illness with approximate case fatality rates of 9 and 36%, respectively, but the transmission of both has remained limited (9). HCoV-OC43 and HCoV-HKU1 infections may be asymptomatic or associated with mild to moderate upper respiratory tract illness; these HCoVs are considered the second most common cause of the common cold (9)...

Fig. 1 Effects of depletion of susceptibles and seasonality on Re by strain and season.
Shown are the estimated multiplicative effects of HCoV-HKU1 incidence (red), HCoV-OC43 incidence (blue), and seasonal forcing (gold) on weekly Res of HCoV-HKU1 (top) and HCoV-OC43 (bottom), with 95% confidence intervals. The black dot (with 95% confidence interval) plotted at the start of each season is the estimated coefficient for that strain and season compared with the 2014–2015 HCoV-HKU1 season. The seasonal forcing spline is set to 1 at the first week of the season (no intercept). On the x-axis, the first “week in season” corresponds to epidemiological week 40.

Fig. 2 Transmission model fits for HCoV-OC43 and HCoV-HKU1.
(A) Weekly percent positive laboratory tests multiplied by percent ILI for HCoV-OC43 (blue) and HCoV-HKU1 (red) in the United States between 5 July 2014 and 29 June 2019 (solid lines) with simulated output from the best-fit SEIRS transmission model (dashed lines). (B and C) Weekly Re values estimated using the Wallinga–Teunis method (points) and simulated Re from the best-fit SEIRS transmission model (line) for HCoV-OC43 and HCoV-HKU1. The opacity of each point is determined by the relative percent ILI multiplied by percent positive laboratory tests in that week relative to the maximum percent ILI multiplied by percent positive laboratory tests for that strain across the study period, which reflects uncertainty in the Re estimate; estimates are more certain (darker points) in weeks with higher incidence.

We summarized the postpandemic SARS-CoV-2 dynamics into the categories of annual outbreaks, biennial outbreaks, sporadic outbreaks, or virtual elimination (tables S2 to S7). Overall, shorter durations of immunity and smaller degrees of cross-immunity from the other betacoronaviruses were associated with greater total incidence of infection by SARS-CoV-2, and autumn establishments and smaller seasonal fluctuations in transmissibility were associated with larger pandemic peak sizes. Model simulations demonstrated the following key points...

...SARS-CoV-2 can proliferate at any time of year...

...If immunity to SARS-CoV-2 is not permanent, it will likely enter into regular circulation...

...High seasonal variation in transmission leads to smaller peak incidence during the initial pandemic wave but larger recurrent wintertime outbreaks...

...If immunity to SARS-CoV-2 is permanent, the virus could disappear for 5 or more years after causing a major outbreak...

...Low levels of cross-immunity from the other betacoronaviruses against SARS-CoV-2 could make SARS-CoV-2 appear to die out, only to resurge after a few years...

Fig. 6 Intermittent social distancing scenarios with current and expanded critical care capacity.
SARS-Cov-2 prevalence (black curves) and critical cases (red curves) under intermittent social distancing (shaded blue regions) without seasonal forcing (A and C) and with seasonal forcing (B and D). Distancing yields a 60% reduction in R0. Critical care capacity is depicted by the solid horizontal black bars, and the on/off thresholds for social distancing are depicted by the dashed horizontal lines. (A) and (B) are the scenarios with current critical care capacity in the United States and (C) and (D) are the scenarios with double the current critical care capacity. The maximal wintertime R0 is 2.2 and for the seasonal scenarios the summertime R0 is 1.3 (40% decline). Prevalence is in black and critical care cases are in red. To the right of each main plot (E to H), the proportion immune over time is depicted in green with the herd immunity threshold (horizontal black bar).

wenty-five kilometers north of Dublin, a masterpiece of Stone Age engineering rises from the hills: a circular structure 12 meters high, almost the area of a U.S. football field, and made up of more than 200,000 tons of earth and stone. Some of the first farmers to arrive in Ireland erected this monument, called Newgrange, nearly 1000 years before Stonehenge or Egypt's first pyramids were built. Archaeologists have assumed it was a ceremonial site and communal tomb—an expression of an egalitarian society.

Now, DNA from a middle-aged man buried in 3200 B.C.E. at the center of this mighty mound suggests otherwise. His genes indicate he had parents so closely related they must have been brother and sister or parent and child.

Across cultures, incest is almost always taboo—except in inbred royal families. Its genetic traces at Newgrange suggest social hierarchy took hold in Ireland earlier than thought, according to a new study. “Maybe we've been arguing too far that [these people were] egalitarian,” says Jessica Smyth, an archaeologist at University College Dublin who was not part of the team.

Previous analyses of ancient genomes have demonstrated common ancestry between the societies of the Atlantic seaboard during the Neolithic7,8,9, while recent modelling of radiocarbon determinations has defined repeat expansions of megalithic architecture from northwest France at a pace that implies more advanced maritime technology than was previously assumed for these regions10. This includes the spread of passage tombs along the Atlantic façade during the fourth millennium BC—a period that also saw the arrival of agriculture in Ireland, alongside other distinct megalithic traditions. These structures reached some of the highest concentrations and diversities known for Europe on the island of Ireland. However, the political systems that underlay these societies remain obscure, as does the genetic input from indigenous Mesolithic hunter-gatherers.

To investigate these issues, we shotgun-sequenced individuals dating to the Irish Mesolithic (n = 2) and Neolithic (n = 42) periods to a median 1.14× coverage (Fig. 1a, Supplementary Tables 1, 2). We imputed 43 of these individuals alongside relevant ancient genomes (Supplementary Table 3), including an additional 20 British and Irish individuals7,9,11. We then merged these individuals with a published dataset of imputed ancient genotypes12 to allow for fine-scale haplotypic inference of population structure13 and estimations of inbreeding. Four key individuals were subsequently sequenced to higher (13–20×) coverage.

We sampled remains from all of the major Irish Neolithic funerary traditions: court tombs, portal tombs, passage tombs, Linkardstown-type burials and natural sites (Fig. 1a, c, Supplementary Information section 1). Within this dataset, the earliest Neolithic human remains from the island—interred at Poulnabrone portal tomb14—are of majority ‘Early_Farmer’ ancestry (as defined by ADMIXTURE modelling15), and show no evidence of inbreeding (Fig. 1a, Extended Data Fig. 1), which implies that, from the very onset, agriculture was accompanied by large-scale maritime colonization...

...Overall, no increase in inbreeding is seen through time in Neolithic Ireland, which indicates that communities maintained sufficient size and communication to avoid matings between relatives of the fifth degree or closer (Fig. 1a). However, we report a single extreme outlier interred within the Newgrange passage tomb—a focal point of the monumental landscape of Brú na Bóinne, a United Nations Educational, Scientific and Cultural Organization world heritage site (Fig. 2a). Incorporating over 200,000 tonnes of earth and stone, this megalithic mound is one of the most spectacular of its kind known from Europe16...

...The exceptional location of these remains is matched by a genomic heritage that—to our knowledge—is unprecedented in ancient genomics. He possessed multiple long runs of homozygosity, each comprising large fractions of individual chromosomes (Fig. 2e, Extended Data Fig. 3a), and totalling to a quarter of the genome (inbreeding coefficient = 0.25). This marks him as the offspring of a first-order incestuous union, which is a near-universal taboo for entwined biological and cultural reasons4. However, given the nature of the interment, his parentage was very likely to have been socially sanctioned...

a, Timeline of analysed Irish genomes with inbreeding coefficients are shown for those with sufficient coverage. All dates are direct and calibrated, excluding that for individual CAK534 (translucent). The key for the sample sites is given in c. The earliest widespread evidence of Neolithic activity (house horizon) is marked with a black line. The Irish Neolithic ends at about 2500 BC. NA, not applicable. b, Stable isotope values for samples from the Irish and British Neolithic (n = 292). The key for the Irish samples is given in c, and samples included in the ancient DNA analysis are outlined in black. British samples are shown as hollow shapes; black, Scotland; grey, England or Wales; circles, pre-3400 BC; squares, post-3400 BC. An infant with Down syndrome (PN07) is labelled; this individual showed isotope values consistent with a high trophic level. c, Site locations for Irish individuals sampled or included in this study coloured by burial type: yellow, court tomb; blue, portal tomb; green, Linkardstown-type; magenta, passage tomb and related; light pink, natural sites; and light blue, the unclassified Ballynahatty7 megalith. Sites outlined in black were included in ancient DNA analysis. d, ChromoPainter13 principal component (PC) analysis of individuals from the Atlantic seaboard of majority Early_Farmer ancestry (n = 57), generated using a matrix of haplotypic length-sharing. Passage tomb outliers in Fig. 2d are labelled. e, fineSTRUCTURE dendrogram derived from the same matrix as in d with five consistent clusters.

a, Front elevation and interior of the Newgrange passage tomb. Photographs by Fáilte Ireland; Photographic Unit, National Monuments Service. b, Plan of chamber, redrawn after ref. 16. Scale bar, 6 m. c, The coefficient of relatedness (pi-HAT) between car004 (an interment from the central monument at Carrowmore)9, and 38 British and Irish Neolithic samples, with the top 5 hits labelled (CAK68 and CAK530 are equal in value). d, Average length of donated haplotypic chunks between all reciprocal pairs of the ‘passage tomb cluster’ (pink; n = 42) and ‘British–Irish cluster’ (grey; n = 1,190) as defined by fineSTRUCTURE in Fig. 1e. The highest values for passage-tomb-cluster pairs are marked along the x axis, with an excess of longer chunks shared between the inferred kin of car004 (CAK533, MB6 and NG10) in c. Darker lines link reciprocal donations. Combined symbols are used for inter-site pairs. e, A sliding window of heterozygosity is plotted for transversions along selected chromosomes of NG10, revealing extreme runs of homozygosity. Scale bar, 50 Mb.

a, Right, the maps show the estimates of shared drift between Irish and British or continental hunter-gatherers (HG) (jittered) from the Mesolithic and Upper Palaeolithic (triangles, Magdalenian culture). Left, the top ten hits with sufficient coverage are cross-compared with one another and with Irish hunter-gatherers in a heat map using the statistic f3(Mbuti; HG1, HG2), in which HG1 and HG2 represent all possible pairs. b, Short and long runs of homozygosity (ROH) spectra in modern and ancient genomes. Hollow shapes indicate direct (rather than imputed) diploid calls. For four Irish samples, both imputed and direct data are presented, showing close agreement. c, Normalized haplotypic length donations from hunter-gatherer populations to Neolithic individuals, arranged by their geographic region (labelled). The top three hunter-gatherer donors are outlined for each individual. Donor hunter-gatherer population colours are as in b; British and northwestern European hunter-gatherers are merged into one donor population (blue).

Curbing carbon emissions while maintaining quality of life is a global challenge for manufacturing processes that will require process innovation. One approach is replacing energy from the burning of carbon-based fuels with energy supplied by “green” electrons. This goal can be achieved in some cases by simply replacing heat supplied by combustion with electrical heating (1). In chemical synthesis, it can also more elegantly supply reaction energy through electrochemistry. On page 1228 of this issue, Leow et al. (2) propose an electrochemical route to ethylene oxide (EO) and propylene oxide (PO) that promises cleaner, more efficient, and more selective processing. Ethylene and propylene were epoxidized electrochemically to EO and PO, respectively, at industrially relevant current densities with Faradaic (electron-specific) selectivities ?70% to the target epoxide (2).

Leow et al. coupled an electrochemical flow cell to homogeneous reactions for an overall reaction, C2H2 + H2O ? C2H2O + H2, for EO synthesis (see the figure). Two electrochemical reactions drive this reaction. Chlorine evolution occurs at the anode, 2Cl? ? 2e? + Cl2, and hydrogen evolution occurs at the cathode, 2H2O + 2e? ? H2 + 2OH?, where e is the charge on the electron. These reactions are not particularly interesting; what is innovative is coupling these two simple reactions with three subsequent, homogeneous chemical reactions. Dissolved chlorine in the anodic solution dissociates into hydrochloric and hypochlorous acid (HCl and HOCl, respectively)...

...Technoeconomic analysis by Leow et al. suggests that this process could scale to produce EO at a cost comparable with current industrial practices with a lower carbon footprint when supplied with renewable energy (2). Such a process would be a carbon-negative path to an important, large-scale commodity chemical. Improvements are still possible, particularly in product selectivity and catalyst selection. Nonetheless, the electrochemical productivity of EO reported in this study is a factor of 10 higher than that of the electrochemical process of Simmrock and Hellemanns (3).

In the United States, chemical manufacture accounts for 28% of total industrial energy demand (1). At present, this demand is largely met by the consumption of fossil fuels, resulting in substantial carbon dioxide (CO2) emissions (2, 3); a recent report showed that the plastics industry alone releases 1.8 billion metric tons of CO2 per year and that replacing fossil fuels–based production methods with ones powered with renewable energy offers a route to reduce net greenhouse gas emissions associated with plastics manufacture (4).

One attractive strategy involves the development of electrochemical systems that produce the necessary raw materials by using renewable electricity (5–8).