Since the first reports of novel pneumonia (COVID-19) in Wuhan, Hubei province, China1,2, there has been considerable discussion on the origin of the causative virus, SARS-CoV-23 (also referred to as HCoV-19)4. Infections with SARS-CoV-2 are now widespread, and as of 11 March 2020, 121,564 cases have been confirmed in more than 110 countries, with 4,373 deaths5.

SARS-CoV-2 is the seventh coronavirus known to infect humans; SARS-CoV, MERS-CoV and SARS-CoV-2 can cause severe disease, whereas HKU1, NL63, OC43 and 229E are associated with mild symptoms6. Here we review what can be deduced about the origin of SARS-CoV-2 from comparative analysis of genomic data. We offer a perspective on the notable features of the SARS-CoV-2 genome and discuss scenarios by which they could have arisen. Our analyses clearly show that SARS-CoV-2 is not a laboratory construct or a purposefully manipulated virus...

...The receptor-binding domain (RBD) in the spike protein is the most variable part of the coronavirus genome1,2. Six RBD amino acids have been shown to be critical for binding to ACE2 receptors and for determining the host range of SARS-CoV-like viruses7. With coordinates based on SARS-CoV, they are Y442, L472, N479, D480, T487 and Y4911, which correspond to L455, F486, Q493, S494, N501 and Y505 in SARS-CoV-27

The second notable feature of SARS-CoV-2 is a polybasic cleavage site (RRAR) at the junction of S1 and S2, the two subunits of the spike8 (Fig. 1b). This allows effective cleavage by furin and other proteases and has a role in determining viral infectivity and host range12. In addition, a leading proline is also inserted at this site in SARS-CoV-2; thus, the inserted sequence is PRRA (Fig. 1b). The turn created by the proline is predicted to result in the addition of O-linked glycans to S673, T678 and S686, which flank the cleavage site and are unique to SARS-CoV-2 (Fig. 1b). Polybasic cleavage sites have not been observed in related ‘lineage B’ betacoronaviruses, although other human betacoronaviruses, including HKU1 (lineage A), have those sites and predicted O-linked glycans13. Given the level of genetic variation in the spike, it is likely that SARS-CoV-2-like viruses with partial or full polybasic cleavage sites will be discovered in other species...

...The function of the predicted O-linked glycans is unclear, but they could create a ‘mucin-like domain’ that shields epitopes or key residues on the SARS-CoV-2 spike protein18. Several viruses utilize mucin-like domains as glycan shields involved immunoevasion18.

It is improbable that SARS-CoV-2 emerged through laboratory manipulation of a related SARS-CoV-like coronavirus. As noted above, the RBD of SARS-CoV-2 is optimized for binding to human ACE2 with an efficient solution different from those previously predicted7,11. Furthermore, if genetic manipulation had been performed, one of the several reverse-genetic systems available for betacoronaviruses would probably have been used19. However, the genetic data irrefutably show that SARS-CoV-2 is not derived from any previously used virus backbone20...

...As many early cases of COVID-19 were linked to the Huanan market in Wuhan1,2, it is possible that an animal source was present at this location. Given the similarity of SARS-CoV-2 to bat SARS-CoV-like coronaviruses2, it is likely that bats serve as reservoir hosts for its progenitor...

...Malayan pangolins (Manis javanica) illegally imported into Guangdong province contain coronaviruses similar to SARS-CoV-221. Although the RaTG13 bat virus remains the closest to SARS-CoV-2 across the genome1, some pangolin coronaviruses exhibit strong similarity to SARS-CoV-2 in the RBD, including all six key RBD residues21 (Fig. 1)...

...Neither the bat betacoronaviruses nor the pangolin betacoronaviruses sampled thus far have polybasic cleavage sites. Although no animal coronavirus has been identified that is sufficiently similar to have served as the direct progenitor of SARS-CoV-2, the diversity of coronaviruses in bats and other species is massively undersampled...

...It is possible that a progenitor of SARS-CoV-2 jumped into humans, acquiring the genomic features described above through adaptation during undetected human-to-human transmission. Once acquired, these adaptations would enable the pandemic to take off and produce a sufficiently large cluster of cases to trigger the surveillance system that detected it1,2.

a, Mutations in contact residues of the SARS-CoV-2 spike protein. The spike protein of SARS-CoV-2 (red bar at top) was aligned against the most closely related SARS-CoV-like coronaviruses and SARS-CoV itself. Key residues in the spike protein that make contact to the ACE2 receptor are marked with blue boxes in both SARS-CoV-2 and related viruses, including SARS-CoV (Urbani strain). b, Acquisition of polybasic cleavage site and O-linked glycans. Both the polybasic cleavage site and the three adjacent predicted O-linked glycans are unique to SARS-CoV-2 and were not previously seen in lineage B betacoronaviruses. Sequences shown are from NCBI GenBank, accession codes MN908947, MN996532, AY278741, KY417146 and MK211376. The pangolin coronavirus sequences are a consensus generated from SRR10168377 and SRR10168378 (NCBI BioProject PRJNA573298)29,30.

Katherine Johnson was the most recognized of the African American “human computers” — female mathematicians who worked at NASA and its predecessor, the National Advisory Committee for Aeronautics (NACA), from the 1930s until the 1980s. Johnson was most proud of the calculations that she contributed to the Apollo 11 mission to place the first human on the Moon. But it was her role producing and checking the trajectory equations for astronaut John Glenn’s pioneering Project Mercury orbital space flight in 1962 that established her professional reputation.

Wider fame for Johnson came in 2016 with the publication of my group biography Hidden Figures, and the release of the film based on it. Asked about the challenges of being black in a segregated workplace, or of having upended the no-women policy in her division’s research meetings, she was most likely to reply: “I was just doing my job.”

A gifted mathematician who always followed her curiosity, Johnson became a powerful symbol of the often-unheralded contributions that women and minority ethnic groups have made to science, technology, mathematics and computing over the course of the twentieth century. Although her fascination with numbers was obvious from childhood — she recalled counting dishes, stars, steps, everything — the possibility of deploying her talent as a professional mathematician was anything but.

Born Katherine Coleman in White Sulphur Springs, West Virginia, she and her three siblings were sent 200 kilometres away by their parents to be educated, because there was no local school beyond sixth grade for those who were called ‘coloured’ students in the pre-civil-rights-era United States. Teachers allowed her to skip several grades in school, and she was just 14 when she entered the historically black West Virginia State College in Institute to study mathematics...

... In 1952 she applied to work at NACA’s research outpost in Hampton, Virginia, then called the Langley Aeronautical Laboratory. She began her career in the all-black, all-female West Area Computing Unit, helmed by mathematician Dorothy Vaughan. Vaughan soon sent her to fill an opening in the Flight Research Division, a group that specialized in tests on actual aeroplanes, rather than wind-tunnel simulations. For five years, Johnson was part of an engineering team that investigated phenomena such as wake turbulence, leading to improved safety for military and commercial aviation...

... The Flight Research Division diverted its attention to spacecraft, and by 1958, Johnson had contributed to ‘Notes on Space Technology’, the agency’s first comprehensive reference document on space flight. By 1959, she had prepared a trajectory analysis for a crewed suborbital flight. The following year, she co-authored the research report ‘Determination of Azimuth Angle at Burnout for Placing a Satellite Over a Selected Earth Position’, laying out the equations that would form the basis of that crewed orbital space flight piloted by Glenn.

Her named credit on the report was a first for a woman in her division, and positioned her to play a part in a mission that enabled the United States to draw even with the Soviet Union — one of the pivotal moments of the space race. In the days leading up to Glenn’s flight, the astronaut asked Johnson — “the girl”, as he called her — to hand-check the trajectory equations that had been input into the IBM 7090 computer. The flight forever linked a black female mathematician to one of the United States’ most glorious achievements.

Une manière commode de faire la connaissance d’une ville est de chercher comment on y travaille, comment on y aime et comment on y meurt. Dans notre petite ville, est-ce l’effet du climat, tout cela se fait ensemble, du même air frénétique et absent. C’est-à-dire qu’on s’y ennuie et qu’on s’y applique à prendre des habitudes. Nos concitoyens travaillent beaucoup, mais toujours pour s’enrichir. Ils s’intéressent surtout au commerce et ils s’occupent d’abord, selon leur expression, de faire des affaires. Naturellement ils ont du goût aussi pour les joies simples, ils aiment les femmes, le cinéma et les bains de mer. Mais, très raisonnablement, ils réservent ces plaisirs pour le samedi soir et le dimanche, essayant, les autres jours de la semaine, de gagner beaucoup d’argent. Le soir, lorsqu’ils quittent leurs bureaux, ils se réunissent à heure fixe dans les cafés, ils se promènent sur le même boulevard ou bien ils se mettent à leurs balcons. Les désirs des plus jeunes sont violents et brefs, tandis que les vices des plus âgés ne dépassent pas les associations de boulomanes, les banquets des amicales et les cercles où l’on joue gros jeu sur le hasard des cartes.

Two hundred years ago, an expedition led by Fabian Gottlieb von Bellingshausen and Mikhail Lazarev discovered mainland Antarctica, the most remote and inhospitable continent. Today, Antarctic is an ice-covered continent where change is emblematic of the impacts humans have on the global climate. Hidden beneath the ice sheets are a rich diversity of terrains and hydrologic systems of mountains, lakes, and dynamic subglacial water networks (1, 2). The changes we are now witnessing (3–5) are concentrated in the low-elevation regions as well as the Antarctic Peninsula, the furthest north part of the continent. Evidence of change comes from satellite measurements of ice mass, velocity (4), and elevations (3). Large floating ice shelves have disintegrated (6), and the location where the ice goes afloat is moving inland (7). Future vulnerabilities arise from interactions with the warming ocean, melting of the ice surface, and the disappearance of the ice shelves. Looking forward, coastal communities around the globe need to know how much sea level will rise, and how much Antarctica will change is one of the greatest unknowns. Both improved models and observations are essential to improve the scientific community’s response to the question of how much sea level will rise over the coming decades and centuries...

...Over the past 100 million years or more, Antarctica shifted from a green tree-covered continent (8) to a continent encased in ice as it became tectonically isolated while the global climate cooled (9). The tectonic isolation of the continent began more than 200 million years ago, when it was at the center of the Gondwana supercontinent with a climate similar to that of modern New Zealand. The supercontinent breakup occurred slowly, first with Africa (170 million years ago), then India (145 million years ago), and last, Australia (90 million years ago), shifting away from what today is Antarctica as the Southern Ocean began to form. The final step occurred 34 million years ago as the Drake Passage (10), between South America and the Antarctic Peninsula, and the Tasmanian Gateway, south of Australia, opened. The global oceans thereby were effectively linked. The Antarctic Circumpolar Current, the strongest ocean current on the planet, began to circulate around the continent, and Antarctica was isolated...

Fig. 1 Development of Antarctic ice together with global CO2 and ocean surface temperature.
(Top) Global CO2. (Bottom) Ocean surface temperature. Onset of East Antarctic ice occurred 34 million years ago as ocean temperatures and CO2 dropped (53, 54). Development of West Antarctica marine ice sheet at 14 million years ago began with the next major drop in global temperature. Two extreme modes of Antarctic ice have occurred since the onset of glaciation in West Antarctica was first covered with ice: ice extending all the way to the continental shelf during cold periods, such as the Last Glacial Maximum 25,000 years ago, and retreat beyond the present extent, with partial collapse of marine portions of Antarctica during some past warm periods (16).

..There are three major components of an ice sheet system: grounded slow-moving ice, fast-flowing ice streams or outlet glaciers and floating ice shelves (Fig. 2). The grounded slow-moving ice contains the vast majority of the ice (Fig. 2) and is in contact with the underlying rocks. This ice moves very slowly by means of internal deformation at rates on the order of 1 m/year (4) and is up to 4775 m thick (17). The fast flowing ice streams and outlet glaciers are conveyor belts that move the ice toward the ocean, are up to 100 km across, and slide rapidly over the underlying topography at rates of up to 4 km/year (4). Although the surface of glaciers and ice streams are fractured by crevasses, water and till (water-saturated sediments) at their base reduce the basal friction and enable their fast flow (18). The grounded Antarctic holds enough ice to raise sea level rise by 58 m (19)...

...East Antarctica is the largest ice sheet on the planet, with thicknesses greater than 4600 m (19). In some areas, the bedrock underlying the ice is above sea level, but extensive portions are below sea level. The top of the ice sheet, Dome A, is at 4200 m over the Gamburtsev Mountains (Figs. 2 and 3), whereas the deepest point, carved by erosion during successive advance and retreat of an ice stream, is located more than 3500 m below sea level under Denman Glacier (19). Beneath the thick ice are large lakes—Vostok (21), 90°E, and Sovietskaya (22)—with up to 1000 m of water (Figs. 2 and 3). These systems have been sealed from the atmosphere for ~34 million years since the onset of Antarctic glaciation. The iconic ice core records of temperature and CO2 come from the deep cores at Vostok [400,000 years (14)], Dome C [800,000 years (23)], and Dome F [720,000 years (24)].

Fig. 2 Structure of the Antarctic Ice Sheet.
(A) East and (B) West Antarctic cross section profiles. (C and D) Location of profiles are shown on (C) surface velocity and (D) subglacial bed topography (17). West Antarctica maximum elevation of 2200 m is nested in the deep Byrd Subglacial Basin, with depths 2500 m below sea level. The East Antarctic Ice Sheet nucleated on the high Gamburtsev Mountains, with the maximum elevation at Dome A reaching 4200 m, covers deep subglacial lakes such as Lake Vostok and has portions that are marine. The portions of the ice sheets with bedrock elevation below sea level are shaded blue.

Fig. 3 Radar cross sections over the Gamburtsev Mountains, Lake Vostok, and West Antarctica.
(Top) Gamburtsev Mountains. (Middle) Lake Vostok. (Bottom) West Antarctica. Location of profiles are approximately along the profiles shown in Fig. 2. Radar layers indicate ice stratigraphy. Ice is deformed as it flows over mountains, but layers remain flat as the ice flows over Lake Vostok, the location of the first deep ice core. The color shading highlights the age of the ice sheets. Basal freeze-on is observed in the Gamburtsev Mountain profile

...Evidence for change

The evidence for recent changes of Antarctic ice is quantified by three independent measurements primarily derived from satellite and airborne systems: decreasing mass from gravity, dropping surface elevation, and increased surface velocities (Fig. 4).

Changes in ice mass are measured from space with the pair of GRACE (Gravity Recovery and Climate Experiment) satellites, which capture changes in the gravity field experienced by each spacecraft as they orbit Earth together (28). The original pair of satellites resolved monthly changes in Antarctic ice mass from 2002 to 2017 (Fig. 4), and a new pair of satellites, GRACE Follow-On, was launched in 2018 to continue the record of the Earth and Antarctic mass changes. The observed changes must be corrected for modeled changes in motion of the solid Earth to include the crust and the mantle rebound owing to past and ongoing ice mass changes. Determining both the Earth structure and the history of past ice sheet changes are the greatest challenges in separating the observed mass changes into the solid Earth component and the changes in ice mass. The GRACE data (28) show mass loss in West Antarctica, focused in the Amundsen and Bellingshausen Sea sectors, and mass gain in some regions of East Antarctica and along Kamb Ice Stream (Fig. 4).

Lowering of the surface elevation has been measured with altimeters from space and aircraft in the same regions where mass loss is observed. Both radar (Cryosat and European Remote Sensing satellites) and laser altimeters [Ice, Cloud, and land Elevation Satellite 1 (ICESat1) and ICESat2 satellites, Operation IceBridge airborne] are used to measure ice surface elevation. Laser observations are impeded by cloud cover, whereas radar measurements penetrate into the upper portions of the snowpack, introducing some ambiguity. Dropping elevation over the 25-year altimetry period is pronounced in the Amundsen and Bellingshausen Sea sectors of West Antarctica and Wilkes Land in East Antarctica (3). Pine Island, Thwaites, and Smith-Pope-Kohler Glaciers experienced the greatest elevation drop over this period, with changes of up to 9 m/year (Fig. 4). Supporting the observed GRACE mass gain, some margins of East Antarctica are increasing in elevation because of increased snowfall (Fig. 4) (29). Along the Siple Coast, the interior of Kamb Ice Stream has thickened at a rate of ~0.65 m/year over the past 20 years because of its stagnation (Fig. 4) (3). Velocity measurements based on interferometric synthetic aperture radar (SAR) measurements and speckle tracking (4) allow the flow of large regions to be observed with accuracies of several tens of meters per year. The changes in ice sheet velocity are striking in the Peninsula, where a substantial acceleration of glaciers feeding the Larsen ice shelves was observed after their collapse, as well as in the Amundsen Sea sector. In this region, Pine Island Glacier’s velocity doubled from the 1990s to the 2010s (Fig. 4), while its grounding line position, accurately estimated by differential interferometric SAR, retreated by more than 30 km (7). The velocity observations are used to calculate the flux of ice discharge into the ocean and, combined with modeled surface accumulation, to estimate the ice mass gain or loss for the different catchment basins. Through an international collaboration, the scientific community has demonstrated the robust agreement between these three different methods and highlighted the ongoing changes of the Antarctic Ice Sheet (5).

Between 1950 and 2000, the average air temperature in the Peninsula increased by 4°C (30). During this warming period, the Larsen A and B ice shelves collapsed in 1995 and 2002, respectively (Fig. 4). The glaciers feeding the Larsen B Ice Shelf sped up after the loss of the backward stress or buttressing (6, 31). Before the Larsen B collapse, the surface of the ice shelf surface was covered by lakes, indicating that warming air temperatures and surface meltwater can destabilize ice shelves, leading to faster flow of Antarctic ice into the global oceans and highlighting the protecting role of ice shelves (32)...

Vulnerabilities

These remote sensing observations allow scientists to observe ice sheet changes and decipher the causes of such changes. Both the ocean surrounding Antarctica and the atmosphere, especially in the Peninsula region, have warmed over the 25-year observational record of ice change (33, 34). Antarctica is losing most of its mass through increased ice flow of the outlet glaciers and ice streams. This contrasts with the Greenland Ice Sheet, where half of the loss is due to faster ice flow and half is due to increased melting of the ice sheet surface (35). Surface melt is not yet a major contributor to ice loss in Antarctica, and global climate models suggest that an increase in snowfall in East Antarctica could partially offset the dynamic mass loss (36). Although these changes have been ongoing for the past three decades, more rapid and dramatic mass loss cannot be excluded...

...The concentration of changes in West Antarctica points to the dominant role the warming ocean plays in recently observed change (39, 40). At the base of the outlet glaciers in the Amundsen Sea, the topography beneath the ice either rises inland or drops. A bed topography dropping inland with ice getting thicker is referred to as a reverse slope. This reverse slope for a marine ice sheet has long been at the core of a concept called the marine ice sheet instability (37). As a glacier retreats across a reverse slope, glacier retreat means thicker ice at the grounding line, and therefore, more ice is leaving the ice sheet, while the region that accumulates snow is reduced. The ice sheet is out of balance. The greater flux of ice results in thinning and additional retreat until a region with an inland rising slope is encountered to stabilize the grounding line (38). In addition to this, ice dynamics imbalance on a reverse slope; the thicker ice at the grounding line means more ice is exposed to warming ocean waters (40). A perturbation can nudge an outlet glacier off a stable point into a region with a reverse slope and have consequences for decades (39, 41). An extreme El Nino event in the 1940s appears to have triggered the grounding line retreat still ongoing in the Pine Island catchment in West Antarctica (42)

Another trigger for rapid and sustained increased ice flux is the collapse of buttressing ice shelves. This concept was widely debated in the science community until the acceleration of the ice flow in the glaciers feeding the Larsen B ice shelf after its collapse in 2003 was observed (6, 31). Shortly before the collapse, this ice shelf surface was covered with lakes, leading to the hypothesis that hydrofracture and loading from lakes can damage an ice shelf sufficiently to induce a catastrophic collapse (32). This mechanism has been incorporated into some ice sheet models (41) but assumes that meltwater is stationary and that little water is transported across an ice shelf. It is now clear that surface water can flow from the grounded ice onto ice shelves (43) and coalesce into rivers atop the ice surface that end as waterfalls at their front (44). Hydrology could therefore have a stabilizing impact on ice sheet mass balance as the distribution of meltwater increases...

Fig. 4 Evolution of the Antarctic Ice Sheet over the past two decades.
(A) Spatial ice mass loss (m.w.e.) estimated from GRACE-collected data over the 2002–2017 period (28). Gray areas show the extension of the floating ice shelves that do not contribute directly to sea level rise. (B) Ice front retreat in the Antarctic Peninsula for the Larsen A, B, and C ice shelves between 1995 and 2017 (6, 31). (C) Change in ice velocity between 2005 and 2017 (meters per year) for glaciers in the Amundsen Sea Sector (4). Black lines represent the ice front and grounding lines. (D) Time series of mass loss (gigatons) and associated uncertainties estimated from GRACE-collected data (28).

Unknowns and future directions

...Increasingly, communities around the globe are asking how much the sea level will rise in the coming decades. Although we now know that the answer for each community must incorporate knowledge of local processes, such as isostatic uplift from unloading of ice at the end of the last glacial period and subsidence owing to sediment compaction, changing ocean volume from Antarctic mass loss remains one of the largest contributors to communities’ unknown future. Gaps in our fundamental knowledge of the bathymetry close to the ice sheet and in regions covered by sea ice and ice shelves, the temperature of the deep water masses, the fate of surface meltwater, and the basal conditions beneath the ice sheets introduce limits into our ability to project the future. It is essential that we refine our projections through expanded observational efforts and improved ice sheet models.

Protecting individual cities with walls and barriers only protects those living behind the protection. An ice sheet–based solution might be more equitable...

Conclusions
Over the 200 years since Antarctica was first spotted, our knowledge of the continent has shifted from the notion of a stagnant piece of ice to a constantly evolving continent interacting with the ocean around, the atmosphere above, and the solid Earth under it and affected by human activities. Advancing our knowledge of the basic history and fundamental processes that control the ice sheet evolution is crucial to future generations...

In December 2019, a new coronavirus caused an outbreak of pulmonary disease in the city of Wuhan, the capital of Hubei province in China, and has since spread globally (1, 2). The virus has been named SARS-CoV-2 (3), because the RNA genome is about 82% identical to the SARS coronavirus (SARS-CoV); both viruses belong to clade b of the genus Betacoronavirus (1, 2). The disease caused by SARS-CoV-2 is called COVID-19. Whereas at the beginning of the outbreak, cases were connected to the Huanan seafood and animal market in Wuhan, efficient human-to-human transmission led to exponential growth in the number of cases. On March 11, the World Health Organization (WHO) declared the outbreak a pandemic. As of March 15, there are >170,000 cumulative cases globally, with a ~3.7% case-fatality rate .

One of the best characterized drug targets among coronaviruses is the main protease (Mpro, also called 3CLpro) (4). Along with the papain-like protease(s), this enzyme is essential for processing the polyproteins that are translated from the viral RNA (5). The Mpro operates at no less than 11 cleavage sites on the large polyprotein 1ab (replicase 1ab, ~790 kDa); the recognition sequence at most sites is Leu-Gln? Ser,Ala,Gly) (? marks the cleavage site). Inhibiting the activity of this enzyme would block viral replication. Since no human proteases with a similar cleavage specificity are known, inhibitors are unlikely to be toxic.

Previously, we designed and synthesized peptidomimetic ?-ketoamides as broad-spectrum inhibitors of the main proteases of betacoronaviruses and alphacoronaviruses as well as the 3C proteases of enteroviruses (6). The best of these compounds (11r; Fig. 1) showed an EC50 of 400 picomolar against MERS-CoV in Huh7 cells as well as low micromolar EC50 values against SARS-CoV and a whole range of enteroviruses in various cell lines, although the antiviral activity seemed to depend to a great extent on the cell type used in the experiments (6). In order to improve the half-life of the compound in plasma, we modified 11r by hiding the P3 - P2 amide bond within a pyridone ring (Fig. 1, green circles), in the expectation that this might prevent cellular proteases from accessing this bond and cleaving it. Further, to increase the solubility of the compound in plasma and to reduce its binding to plasma proteins, we replaced the hydrophobic cinnamoyl moiety by the somewhat less hydrophobic Boc group (Fig. 1, red circles) to give 13a (see scheme S1 for synthesis).

Fig. 1 Chemical structures of ?-ketoamide inhibitors 11r, 13a, 13b, and 14b. Colored circles highlight the modifications from one development step to the next (see text).

Where on Earth, wondered Henri Weimerskirch, were all the penguins? It was early 2017. Colleagues had sent the seabird ecologist aerial photos of Île aux Cochons, a barren volcanic island halfway between Madagascar and Antarctica that humans rarely visit. The images revealed vast areas of bare rock that, just a few decades before, had been crowded with some 500,000 pairs of nesting king penguins and their chicks. It appeared that the colony—the world’s largest king penguin aggregation and the second biggest colony of any of the 18 penguin species—had shrunk by 90%. Nearly 900,000 of the regal, meter-high, black, white, and orange birds had disappeared without a trace. “It was really incredible, completely unexpected,” recalls Weimerskirch, who works at the French national research agency CNRS...
...King penguins should be relatively easy to study. Unlike their ice-bound cousins, such as emperor penguins, king penguins live on islands dotting the subantarctic region. That means they can be reliably and repeatedly counted in satellite images over time, and scientists can camp alongside their breeding colonies to observe them. (Other ice-dependent species, like emperor penguins, are more peripatetic.) During the lengthy breeding season, the parents trade off tasks, with one incubating eggs or rearing fluffy brown chicks while the other heads to sea to catch fish and other sea creatures. These foraging round-trips can cover 500 kilometers or more, electronic tags attached to the birds have shown.



...REAMS OF DATA remain to be digested. But the researchers have already ruled out some possible explanations for the massive penguin decline. Land predators, for instance, don’t seem to have played a role. Examinations of chicks and adult penguins, as well as excavated bones, revealed no signs of cat or mouse bites, and the team’s cameras recorded no attacks. (Rabbits, seen on previous expeditions, were curiously missing.)Nor, it seems, had the penguins simply moved somewhere nearby. A second smaller colony on the island, a natural site for relocation, had just an estimated 17,000 pairs, not enough to explain the massive drop-off in the main group. And Bost says there’s no obvious indication—in satellite images, for instance—that the colony relocated to some other island.

That leaves one main explanation, Bost says: “If the penguins are not here, they died.” But what killed them?

Not disease, apparently. The team is waiting on final blood analyses, but they saw few ailing birds or fresh corpses. “We thought we’d see carrion, individuals in bad condition,” Chaigne says. But the birds looked healthy...

...Evidence that a warming ocean could threaten the penguins comes from a 2015 study that Bost and his colleagues did at a smaller king penguin colony, on Possession Island, some 160 kilometers west of Île aux Cochons... The study, published in Nature Communications, analyzed 124 foraging routes taken by 120 tagged birds over 16 years. It found that in years when the polar front moved south, the penguins had to travel hundreds of kilometers farther. During “these very unfavorable environmental conditions,” the researchers wrote, “the penguin breeding population experienced a 34% decline.”

Building on that study, a 2018 paper published in Nature Climate Change forecast that warming seas and other environmental changes could cut king penguin numbers by half by the end of the century.

Whether that scenario explains the Île aux Cochons crash may never be entirely clear...