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In early 2018, due in part to a severe and extended meteorological drought, Cape Town was at risk of being one of the first major metropolitan areas in the world to run out of water. The magnitude of the crisis was exacerbated by the fact that such a prolonged and severe drought was both unanticipated and unpredicted. In this work we analyze data from both observations and seasonal forecasts made as part of the North American Multi-Model Ensemble (NMME) to better understand the predictability of rainfall in the Cape Town (CT) region. We find that there are statistically significant correlations between observed CT rainfall and sea surface temperatures in the tropical Atlantic (~ 0.45) as well as a pattern of 200mb geopotential height (z200) anomalies resembling the Southern Annular Mode (SAM; ~0.4). Examination of hindcasts from the NMME demonstrates that the models accurately reproduce the observed correlation between CT rainfall and z200 anomalies. However, they fail to reproduce correlations between CT rainfall and the tropical South Atlantic. Decomposition of the correlations into contributions from predictable and unpredictable components indicates that CT rainfall in the models is dominated by unpredicted atmospheric variability (correlation ~0.84) relative to predicted (correlation ~0.14), which may be related to the failure to simulate the connection with the tropical Atlantic.

Southern Ocean bathymetry constrains the path of the Antarctic Circumpolar Current (ACC), but the bathymetric influence on the coupled ocean–atmosphere system is poorly understood. Here, we investigate this impact by respectively flattening large topographic barriers around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers impact both the wind and buoyancy forcing of the ACC transport, which increases by between 4% and 14% when barriers are removed individually and by 56% when all barriers are removed simultaneously. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea. When the barriers are removed, zonal flattening of the currents leads to sea surface temperature (SST) anomalies that strongly correlate to precipitation anomalies, with correlation coefficients ranging between r = 0.92 and r = 0.97 in the four experiments. The SST anomalies correlate to the surface winds too in some locations. However, they also generate circumpolar waves of sea level pressure (SLP) anomalies, which induce remote wind speed changes that are unconnected to the underlying SST field. The meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau, and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on surface winds. However, bathymetry-induced wind changes are too small to affect the overall wave-3 asymmetry in the Southern Hemisphere westerlies. Removal of Southern Hemisphere orography is also inconsequential to the wave-3 pattern. Significance Statement Several studies in the past have pointed to the controlling effect of bathymetry on currents in the Southern Ocean circulation, but a clear idea of the importance of the major topographic barriers in the Southern Ocean is lacking. By removing these barriers systematically in a coupled climate model, we can evaluate their impact on several important components of the climate system, such as the Antarctic Circumpolar Current (ACC) pathways and strength, Antarctic Bottom Water formation, sea surface temperature, overlying winds, air–sea fluxes, and even precipitation. This helps in our understanding of what controls the pathways of the ACC and how much it matters for climate.

Earth's hydrological cycle is expected to intensify in response to global warming, with a “wet-gets-wetter, dry-gets-drier” response anticipated over the ocean. Subtropical regions (∼15°–30°N/S) are predicted to become drier, yet proxy evidence from past warm climates suggests these regions may be characterized by wetter conditions. Here we use an integrated data-modeling approach to reconstruct global and zonal-mean rainfall patterns during the early Eocene (∼56–48 million years ago). The Deep-Time Model Intercomparison Project (DeepMIP) model ensemble indicates that the mid- (30°–60°N/S) and high-latitudes (>60°N/S) are characterized by a thermodynamically dominated hydrological response to warming and overall wetter conditions. The tropical band (0°–15°N/S) is also characterized by wetter conditions, with several DeepMIP models simulating narrowing of the Inter-Tropical Convergence Zone. However, the latter is not evident from the proxy data. The subtropics are characterized by negative precipitation-evaporation anomalies (i.e., drier conditions) in the DeepMIP models, but there is surprisingly large inter-model variability in mean annual precipitation (MAP). Intriguingly, we find that models with weaker meridional temperature gradients (e.g., CESM, GFDL) are characterized by a reduction in subtropical moisture divergence, leading to an increase in MAP. These model simulations agree more closely with our new proxy-derived precipitation reconstructions and other key climate metrics and imply that the early Eocene was characterized by reduced subtropical moisture divergence. If the meridional temperature gradient was even weaker than suggested by those DeepMIP models, circulation-induced changes may have outcompeted thermodynamic changes, leading to wetter subtropics. This highlights the importance of accurately reconstructing zonal temperature gradients when reconstructing past rainfall patterns.

The Miocene epoch, spanning 23.03-5.33Ma, was a dynamic climate of sustained, polar-amplified warmth that peaked during the Miocene Climatic Optimum (16.75-14.5Ma). Miocene atmospheric CO2 concentrations are typically reconstructed between 300-600 ppmv with estimates as high as 800-1100 ppmv during the MCO. With surface temperature reconstructions pointing to substantial midlatitude and polar warmth, it is unclear what processes maintained the much weaker-than-modern equator-to-pole temperature gradient. Emanating from community discussions at MioMeet (hosted by the Bolin Centre for Climate Research in 2019), Burls et al. (2021) synthesize several Miocene climate modeling efforts, together with available terrestrial and ocean surface temperature reconstructions. The range of model-data agreement was evaluated, highlighting robust mechanisms operating across the Miocene modelling efforts, as well as the regions where the differences across models (coming from a combination of model differences in imposed non-CO2 Miocene boundary conditions and model feedback strengths) result in a large spread in warming responses. This MioMIP1 effort was an ensemble of opportunity: the models, boundary conditions, and reference datasets were state-of-the-art, but also inhomogeneous and not ideal for a formal intermodel comparison effort. Building on MioMIP1, the Miocene community is currently drafting the experimental design for a coordinated set of MioMIP2 simulations wherein participating modelling groups will use common boundary conditions. This talk will review the take-home findings from MioMIP1 and the status of the community’s MioMIP2 effort.

The mid-Pliocene (∼3 Ma) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures, and it is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (due to the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. Note that the dynamic effect plays a more important role than the thermodynamic effect in regional precipitation minus evaporation (PmE) changes (i.e., northward ITCZ shift and wetter northern Indian Ocean). The thermodynamic effect is offset to some extent by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth's energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1∘ northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and, hence, altering mid-Pliocene hydroclimate.

The presentation will focus around the impact that major topographic features in the Southern Ocean have on the path of the Antarctic Circumpolar Current (ACC), and their relatively unknown role in the coupled ocean-atmosphere system. We investigate their influence by respectively flattening the bathymetry around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers lead to an increase in the ACC transport of between 3% and 14% in the four simulations. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea, affecting the deep overturning cell. When the barriers are removed, zonal flattening of the currents leads to SST anomalies upstream and downstream of their locations. Interestingly, these SST anomalies strongly correlate to precipitation in the overlying atmosphere, with correlation coefficients ranging between r=0.92 and r=0.97 in the four experiments. Windspeed anomalies are also positively correlated to SST anomalies in some locations but other forcing factors obscure this correlation in general. Meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on overlying winds., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Pliocene Epoch was the last time in Earth's history that atmospheric CO2 levels exceeded the elevated levels seen today. With geography similar to the present day, the Pliocene serves as a potential analog for future warming. However, sea surface temperature (SST) reconstructions reveal less warming in the Tropical Warm Pool (TWP) than climate models predict for future warming. This discrepancy suggests that climate models could be missing a cloud radiative damping mechanism in the TWP. To explore this, we use the Single Column Atmosphere Model v6 to simulate the TWP and systematically perturb parameters in the Zhang-McFarlane deep convection scheme. We do so without temperature relaxation at control and +4 degrees C prescribed SSTs. We then test the significance (alpha = 0.05) of the ordinary least-squares regression coefficients with respect to cloud properties. We find that precipitation efficiency (c0_ocn) is not significant with respect to changes in most cloud variables. Increased reevaporation of precipitation (ke) correlates most strongly with greater specific humidity, and hence, greater net clearsky forcing. Net cloud forcing (CF) decreases as the entrainment parameter (dmpdz) becomes less negative due to substantially less negative shortwave CF. A longer deep convection timescale (tau) weakly correlates to a decrease in longwave CF and increased shortwave CF. These correlations and their physical explanations provide a foundation for research into a cloud radiative damping mechanism in climate models., Journal of Student-Scientists' Research, Vol. 3 (2021)

The Pliocene is often seen as a potential analog for future climate change because of a similar configuration of continents and CO2 concentration as compared to the present day. A notable characteristic of the Pliocene is its weak mean east-west sea surface temperature (SST) gradient and meridional SST gradient in the Pacific. These reduced gradients could affect the global climate via the weakening of the Walker Circulation and of Hadley cells. In Burls and Fedorov 2014 (BF2014), by altering extra-tropical and tropical cloud albedo, these important characteristics were successfully reproduced using a global climate model (GCM). Here we take the resulting SST field from this Pliocene-like simulation, as well as other SST fields from the BF2014 study, and use them as a boundary parameter for another GCM, SPEEDY-IER. SPEEDY-IER is an atmospheric model that allows for the tracing of oxygen isotopes, namely O16 and O18. The ratio of these isotopes, d18O , has a known correlation with temperature and can be observed in the fossil record. Our results demonstrate the first-order control that temperature has on the d18O of precipitation in the mid- to high- latitudes, where experiments with a reduced meridional temperature gradient experience enrichment of d18O of precipitation in the high latitudes. In the future, d18O of precipitation derived from land-based fossil records can be used to verify our results., Journal of Student-Scientists' Research, Vol. 2 (2020)

Southern hemisphere subtropical anticyclones are projected to change in a warmer climate during both austral summer and winter. A recent study of CMIP 5 & 6 projections found a combination of local diabatic heating changes and static-stability-induced changes in baroclinic eddy growth as the dominant drivers. Yet the underlying mechanisms forcing these changes still remain uninvestigated. This study aims to enhance our mechanistic understanding of what drives these Southern Hemisphere anticyclones changes during both seasons. Using an AGCM, we decompose the response to CO2-induced warming into two components: (1) the fast atmospheric response to direct CO2 radiative forcing, and (2) the slow atmospheric response due to indirect sea surface temperature warming. Additionally, we isolate the influence of tropical diabatic heating with AGCM added heating experiments. As a complement to our numerical AGCM experiments, we analyze the Atmospheric and Cloud Feedback Model Intercomparison Project experiments. Results from sensitivity experiments show that slow subtropical sea surface temperature warming primarily forces the projected changes in subtropical anticyclones through baroclinicity change. Fast CO2 atmospheric radiative forcing on the other hand plays a secondary role, with the most notable exception being the South Atlantic subtropical anticyclone in austral winter, where it opposes the forcing by sea surface temperature changes resulting in a muted net response. Lastly, we find that tropical diabatic heating changes only significantly influence Southern Hemisphere subtropical anticyclone changes through tropospheric wind shear changes during austral winter.

Ocean dynamics in the equatorial Pacific drive tropical climate patterns that affect marine and terrestrial ecosystems worldwide. How this region will respond to global warming has profound implications for global climate, economic stability and ecosystem health. As a result, numerous studies have investigated equatorial Pacific dynamics during the Pliocene (5.3–2.6 million years ago) and late Miocene (around 6 million years ago) as an analogue for the future behaviour of the region under global warming1–12. Palaeoceanographic records from this time present an apparent paradox with proxy evidence of a reduced east–west sea surface temperature gradient along the equatorial Pacific1,3,7,8—indicative of reduced wind-driven upwelling—conflicting with evidence of enhanced biological productivity in the east Pacific13–15 that typically results from stronger upwelling. Here we reconcile these observations by providing new evidence for a radically different-from-modern circulation regime in the early Pliocene/late Miocene16 that results in older, more acidic and more nutrient-rich water reaching the equatorial Pacific. These results provide a mechanism for enhanced productivity in the early Pliocene/late Miocene east Pacific even in the presence of weaker wind-driven upwelling. Our findings shed new light on equatorial Pacific dynamics and help to constrain the potential changes they will undergo in the near future, given that the Earth is expected to reach Pliocene-like levels of warming in the next century. New proxy data for ocean pH and an ocean–atmosphere model show that a radically different ocean circulation led to decoupling of ocean productivity and upwelling in the equatorial Pacific Ocean 3–6 million years ago.

Southwestern North America, like many subtropical regions, is predicted to become drier in response to anthropogenic warming. However, during the Pliocene, when carbon dioxide was above pre-industrial levels, multiple lines of evidence suggest that southwestern North America was much wetter. While existing explanations for a wet Pliocene invoke increases in winter rain, recent modeling studies hypothesize that summer rain may have also played an important role. Here, we present the first direct evidence for an intensified Pliocene monsoon in southwestern North America using leaf wax hydrogen isotopes. These new records provide evidence that the Pliocene featured an intensified and expanded North American Monsoon. Using proxies and isotope-enabled model simulations, we show that monsoon intensification is linked to amplified warming on the southern California margin relative to the tropical Pacific. This mechanism has clear relevance for understanding present-day monsoon variations, since we show that intervals of amplified subtropical warming on the California margin, as are seen during modern California margin heat waves, are associated with a stronger monsoon. Since marine heat waves are predicted to increase in frequency, the future may bring intervals of `Pliocene-like' rainfall that co-exist with intensifying megadrought in southwestern North America, with implications for ecosystems, human infrastructure, and water resources

Purpose Drawing on experience of working in the area of mental health and the environment, key issues are examined, and the theoretical framework is explained, including the benefits to communities and to the local environment of working with nature. Design/methodology/approach The interview gave an opportunity for development of ideas underlying concepts including the natural health service, green health literacy and changes in behaviour during the pandemic. Findings The ways in which people and the environment benefit from interaction with nature are becoming well understood; in a sustainable model, the value of the local environment is appreciated and will benefit from the care of those involved in relevant activities. There is a need for targeted training for health professionals, environment agencies’ staff and the voluntary sectors. Research limitations/implications The economic value of nature as a contributing factor in to mental health is an area for research which could have major influence in policymaking. A meeting of a number of disciplines could further bring together social capital, health economics and ecology. Practical implications Projects that are sustainable in every sense are those which are long term, whose value can be measured in environmental and economic terms. Social implications Working models have been developed that involve people on the fringes of society and people with disabilities; they often become the movers in local organisations. Originality/value This is an extremely wide-ranging assessment of developments in the relationship between mental health and nature.

Subtropical anticyclones and midlatitude storm tracks are key components of the large-scale atmospheric circulation. Focusing on the Southern Hemisphere, the seasonality of the three dominant subtropical anticyclones, situated over the South Pacific, South Atlantic, and south Indian Ocean basins, has a large influence on local weather and climate within South America, southern Africa, and Australia, respectively. Generally speaking, sea level pressure within the Southern Hemisphere subtropics reaches its seasonal maximum during the winter season when the Southern Hemisphere Hadley cell is at its strongest. One exception to this is the seasonal evolution of the South Pacific subtropical anticyclone. While winter maxima are seen in the South Atlantic and south Indian subtropical anticyclones, the South Pacific subtropical anticyclone reaches its seasonal maximum during local spring with elevated values extending into summer. In this study, we investigate the hypothesis that the strength of the austral summer South Pacific subtropical anticyclone is largely due to heating over the South Pacific convergence zone. Using added-cooling and added-heating atmospheric general circulation model experiments to artificially change the strength of austral summer diabatic heating over the South Pacific convergence zone, our results show that increased heating, through increased upper-level divergence, triggers a Rossby wave train that extends into the Southern Hemisphere midlatitudes. This propagating Rossby wave train creates a high and low sea level pressure pattern that projects onto the center of the South Pacific subtropical anticyclone to intensify its area and strength.

Multidecadal variability of the Atlantic Meridional Overturning Circulation (AMOC) plays a vital role in Earth’s climate variability. Climate change has the potential to alter the causes and characteristics of AMOC multidecadal variability. Here we use a coupled climate model to simulate AMOC multidecadal variability under three distinct atmospheric CO2 concentrations: Last Glacial Maximum, preindustrial, and 4 × preindustrial levels. Firstly, we discover that AMOC multidecadal variability exhibits a shortened period and a reduced amplitude with increasing atmospheric CO2. We find that these changes in AMOC variability are largely related to enhanced ocean stratification in the subpolar North Atlantic with increasing CO2 which in turn changes the characteristics of westward propagating oceanic baroclinic Rossby waves. Our analysis indicates that the shortened period is primarily due to the increased speed of free oceanic Rossby waves, and the reduced amplitude is mainly due to the reduced magnitude of atmospherically-forced oceanic Rossby waves. Mean flow effects, in the form of eastward mean zonal advection and westward geostrophic self-advection, need to be considered as they largely increase the speed of Rossby waves and hence allow for a better estimate of the changes in the period and amplitude of AMOC variability. Secondly, to explore the possible linkage between atmospheric variability and AMOC fluctuations under each CO2 concentration in a qualitative manner, we analyze the relationship between the North Atlantic Oscillation (NAO) and the AMOC and find a significant negative correlation between the two only under the preindustrial levels where the NAO leads the AMOC by 3–11 years.

Wind power, defined as the energy received by the ocean from wind, has been identified as a potentially viable precursor of ENSO. The correlation between tropical Pacific wind power anomalies and eastern equatorial Pacific sea surface temperature anomalies can be enhanced over a range of lead times by applying an empirical adjusted framework that accounts for both the underlying climatological state upon which a wind power perturbation acts and the directionality of wind anomalies. Linear regression is used to assess the seasonal prediction skill of adjusted wind power in comparison to unadjusted, as well as the conventional ENSO predictors wind stress and warm water volume. The forecast skill of each regression model is evaluated in a 1800-yr preindustrial climate simulation (CESM-LENS), as well as 23 years of observations. The simulation results show that each predictor’s effectiveness varies considerably with the sample record, providing a measure of the uncertainty involved in evaluating prediction skill based on the short observational record. The influence of climatological biases is however a demonstrable concern for results from the simulated climate system. Despite the short record, the observational analysis indicates that adjusted wind power skill is comparable to the conventional dynamical predictors and notably is significantly more predictable than unadjusted wind power when initialized in the summer. Moreover, the adjusted framework results in a reduction of error when evaluating wind power associated with wind bursts, reinforcing previous findings that the adjusted framework is particularly useful for capturing the ENSO response to westerly wind bursts.

More than 6 months into the pandemic, our knowledge around COVID-19 continues to develop rapidly. The cases of COVID-19 range from asymptomatic to severe, but the vast majority of patients will experience mild to moderate symptoms and will not require hospitalisation [1]. We have previously conducted a rapid review of the literature to identify which symptoms and signs might differentiate mild and moderate from severe cases of COVID-19 [2]. Since then and as more data are being gathered, there is increasing evidence of a “long-tail” of COVID-19 related illness [3]. A community app developed at King’s College London, which tracks patients’ symptoms, has shown that about 10% of individuals with COVID-19 had symptoms at 25 days and 5% were still ill one month later (https://covid19.joinzoe.com/). Some individuals with COVID-19 have reported “fatigue, headaches and tingling nerves” that lasted months after symptom onset [4]. Yet, the evidence to date remains fragmented as to the onset of symptoms and clinical features, how long symptoms may last and how this relates to the severity of the initial illness. A better understanding of patients’ projected recovery from COVID-19 can help both patients and doctors in knowing what to expect. It may also help identify people who are not recovering in the anticipated timeframe so they can be provided additional rehabilitation or investigated for a secondary cause of their symptoms where necessary. Forming a better idea of what the main symptoms and clinical features of the illness are is important for organizations such as Public Health England (PHE) in the UK and the CDC in the US, which continue to update the list of key symptoms to inform healthcare professionals and the public. It will also be relevant to organisations such as NHS England, which have recently launched an online COVID-19 rehab service supporting patients suffering long-term effects of the disease (https://www.england.nhs.uk/2020/07/nhs-to-launch-ground-breaking-online-covid-19-rehab-service/).

StatementThe authors have withdrawn their manuscript owing to a reporting error that we have identified in the conduct of this updated systematic review. On 7thMarch 2022 we made changes to the original protocol published in F1000, to highlight the need to keep up with the evolving landscape of Covid-19 and Covid-19 research and focus on comparative, controlled studies. The revisions included also changes in data extraction and analysis that would be needed to do so. These changes were done in consultation with members of the Long COVID Support Group. However, we omitted to publicize these changes in an accessible, modified version of our protocol, and/or by updating our preregistered PROSPERO record (CRD42020211131) and F1000 publication, prior to commencing and completing these stages of the process. In this manuscript, which reports the revised analyses, we have consequently also omitted to explicitly describe these changes as important deviations from the published protocol. Additionally, following rapid, sustained, and continuous growth in the conduct and reporting of eligible primary studies, it has become clear that, with or without the changes described above, we do not have sufficient capacity or resources to transition our baseline systematic review to being regularly updated using a living systematic review approach. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

The contents of this Model_Data directory are associated with Bhattacharya et al. 2022, Expansion and Intensification of the North American Monsoon in the Pliocene (AGU Advances) Minmin_SST_iCAM: contains the monthly climatological output of iCAM5 forced using the SSTs from Fu et al 2022. Separate file for each month, with all variables. 01=January, 02 = February, etc. Sensitivity_Simulations contain the simulations we performed with uniform warming and perturbed subtropical/tropical gradient. These are in a separate folder, and the experiment is indicated in file nomenclature: …..mhw_1.mon2.ncl = 1 times marine heat wave pattern …..mhw_2.mon2.ncl = 1 times marine heat wave pattern …..mhw_3.mon2.ncl = 1 times marine heat wave pattern …..mhw_4.mon2.ncl = 1 times marine heat wave pattern …..uniwar_1.mon2.ncl = 1 times marine heat wave pattern …..uniwar_2.mon2.ncl = 1 times marine heat wave pattern …..uniwar_3.mon2.ncl = 1 times marine heat wave pattern …..uniwar_4.mon2.ncl = 1 times marine heat wave pattern In this case, each file is a separate variable, and contains monthly climatologies for each year. All variable names follow standard CESM naming protocols, and are in standard netcdf formats.

The Pliocene epoch offers insights into future climate change, with near-modern atmospheric pCO2 and global mean surface temperature estimated to be 3-4°C above pre-industrial. The discrepancy in the hydrological response seen between simulations of future global warming and early Pliocene simulations is hypothesized to result from reduced SST gradients in the early Pliocene. However, the interpretation of Pliocene SST proxies is still debated, generating uncertainty about the reduced gradient scenario. One avenue toward reducing uncertainty in Pliocene warming patterns is to establish the degree of dynamical consistency between Pliocene SST reconstructions and hydrological cycle reconstructions. To this end, hydrological cycle reconstructions are needed in regions where water isotopic signals are predicted to be uniquely sensitive to Pliocene SST gradient changes. Here, we seek to identify these regions using an isotope-enabled GCM, iCAM5, to model the distribution of water isotopes in precipitation in response to four climatological SST and sea-ice fields representing modern, abrupt 4xCO­­2, late Pliocene and early Pliocene climates. We identify two regions with distinct precipitation isotope fingerprints resulting from early Pliocene SST gradients. The first region, the Indo-Pacific warm pool, is characterized by isotopic enrichment due to weakened convection and a reduced amount effect. The second region, the Sahel, is characterized by isotopic depletion due to more intense and widespread precipitation. A model-proxy comparison with available precipitation proxies in Africa provides promising initial results. However, additional proxy reconstructions are needed in both target regions to provide robust tests of dynamical consistency with current early Pliocene SST reconstructions.

Several oceanic and atmospheric mechanisms have been put forward to describe the response of the tropical Pacific to global warming. Still uncertainties persist in their interaction and relative importance, with projections varying substantially across climate models. When we turn to the last time in Earth’s history that atmospheric CO2 estimates exceed 400 ppm, the Pliocene, several apparent paradoxes appear, clouding our view of the tropical Pacific during the Pliocene and its utility as a potential analogue for future warming. However, when proper consideration is given to the timescales associated with the oceanic and atmospheric mechanisms that support tropical Pacific climate variability, several of these apparent paradoxes can be resolved. The first apparent paradox is between the reduced east-west SST gradient (weaker Walker Circulation) mean state reconstructions for the Pliocene and the strengthening of the east-west SST gradient during 20th century warming. This paradox can be resolved by considering the transient versus equilibrium processes involved in the response to global warming. The second apparent paradox is evidence for ENSO during the Pliocene even while the mean state resembled more El Nino-like (i.e., El Padre) conditions. This apparent paradox is resolved by the relative importance of coupled feedbacks, other than the thermocline feedback, generating inter-annual variability in the Pliocene. Thirdly, an apparent paradox between the reduced Pliocene east-west SST gradient, indicative of reduced wind-driven upwelling, and evidence of enhanced biological productivity in the east Pacific where productivity is typically driven by upwelling. This apparent paradox can be reconciled by evidence for older, more acidic, and nutrient-rich water reaching the equatorial Pacific by way of a Pacific meridional overturning circulation during the Pliocene, providing a mechanism for enhanced productivity existing alongside a reduced east-west SST gradient.

Geologic intervals of sustained warmth such as the mid-Pliocene warm period can inform our understanding of future climate change, including the long-term consequences of oceanic uptake of anthropogenic carbon. Here we generate carbon isotope records and synthesize existing records to reconstruct the position of water masses and determine circulation patterns in the deep Pacific Ocean. We show that the mid-depth carbon isotope gradient in the North Pacific was reversed during the mid-Pliocene in comparison to today, which implies water flowed from north to south and deep-water formation likely formed in the subarctic North Pacific Deep Water. An isotopically enabled climate model that simulates this North Pacific Deep Water reproduces a similar carbon isotope pattern. Modelled levels of dissolved inorganic carbon (DIC) content in the North Pacific decreases slightly, though the amount of carbon stored in the ocean actually increases by 1.6% relative to modern due to an increase in DIC in the surface ocean. Although the modelled Pliocene ocean maintains a carbon budget similar to the present, the change in deep ocean circulation configuration causes pronounced downstream changes in biogeochemistry.

Modern ocean circulation is driven by formation of deep waters in the North Atlantic and Southern Oceans. Despite the cold temperatures at high latitudes, the North Pacific exhibits no modern deep-water formation, due to the strong halocline in the subpolar North Pacific Ocean. However, modelling results suggest the halocline was weak during the Pliocene, allowing the formation of North Pacific Deep Water (NPDW). Here we compare the oxygen isotopes from benthic foraminifera at two sites in the Northwest Pacific Ocean, ODP Sites 1208 (3346 m) and 1209 (2387 m) to understand how NPDW varied over the Plio-Pleistocene (3.3 to 2.6 Ma). While in the modern the water that occupies the deep Pacific is homogenous, during the Pliocene there was a ~0.5 per mill gradient at times between sites 1208 and 1209, with, surprisingly, more positive δ18O values observed at the shallower 1209. The disparity in oxygen isotopes suggests different water masses over the two sites over the Plio-Pleistocene. Oxygen isotopes of foraminifera record temperature and the δ18O of seawater which loosely correlates with salinity in the modern surface oceans, with more positive δ18O values generally representing more saline, colder, and therefore more dense waters. High latitude processes like sea ice formation could result in a decoupling of salinity from δ18O of seawater. We suggest that the divergences in oxygen isotopes are the result of Site 1208 being bathed in southern-sourced waters, while Site 1209 is bathed in deep waters formed in the North Pacific. Modelling results suggest NPDW is a warm, saline water mass. That the divergence in δ18O values between the two sites is not constant throughout this period suggests that the strength of NPDW export may have fluctuated over this interval. Future work includes Mg/Ca analyses at Site 1209 to compare with the existing record at 1208 to examine the temperature and δ18O of seawater differences between these sites.

The Eocene-Oligocene Transition (EOT) marks the shift from greenhouse to icehouse conditions at 34 Ma, when a permanent ice sheet developed on Antarctica. Climate modeling studies have recently assessed the drivers of the transition globally. Here we revisit those experiments for a detailed study of the southern high latitudes in comparison to the growing number of mean annual sea surface temperature (SST) and mean air temperature (MAT) proxy reconstructions, allowing us to assess proxy-model temperature agreement and refine estimates for the magnitude of the pCO forcing of the EOT. We compile and update published proxy temperature records on and around Antarctica for the late Eocene (38-34 Ma) and early Oligocene (34-30 Ma). Compiled SST proxies cool by up to 3°C and MAT by up to 4°C between the timeslices. Proxy data were compared to previous climate model simulations representing pre- and post-EOT, typically forced with a halving of pCO. We scaled the model outputs to identify the magnitude of pCO change needed to drive a commensurate change in temperature to best fit the temperature proxies. The multi-model ensemble needs a 30 or 33% decrease in pCO, to best fit MAT or SST proxies respectively, a difference of just 3%. These proxy-model intercomparisons identify pCO as the primary forcing of EOT cooling, with a magnitude (-200 or -243 ppmv) approaching that of the pCO proxies (-150 ppmv). However individual model estimates span -66 to -375 ppmv, thus proxy-model uncertainties are dominated by model divergence.

Accurate estimates of past global mean surface temperature (GMST) help to contextualise future climate change and are required to estimate the sensitivity of the climate system to CO2 forcing through Earth's history. Previous GMST estimates for the latest Paleocene and early Eocene (∼57 to 48 million years ago) span a wide range (∼9 to 23 ∘C higher than pre-industrial) and prevent an accurate assessment of climate sensitivity during this extreme greenhouse climate interval. Using the most recent data compilations, we employ a multi-method experimental framework to calculate GMST during the three DeepMIP target intervals: (1) the latest Paleocene (∼57 Ma), (2) the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma), and (3) the early Eocene Climatic Optimum (EECO; 53.3 to 49.1 Ma). Using six different methodologies, we find that the average GMST estimate (66 % confidence) during the latest Paleocene, PETM, and EECO was 26.3 ∘C (22.3 to 28.3 ∘C), 31.6 ∘C (27.2 to 34.5 ∘C), and 27.0 ∘C (23.2 to 29.7 ∘C), respectively. GMST estimates from the EECO are ∼10 to 16 ∘C warmer than pre-industrial, higher than the estimate given by the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (9 to 14 ∘C higher than pre-industrial). Leveraging the large “signal” associated with these extreme warm climates, we combine estimates of GMST and CO2 from the latest Paleocene, PETM, and EECO to calculate gross estimates of the average climate sensitivity between the early Paleogene and today. We demonstrate that “bulk” equilibrium climate sensitivity (ECS; 66 % confidence) during the latest Paleocene, PETM, and EECO is 4.5 ∘C (2.4 to 6.8 ∘C), 3.6 ∘C (2.3 to 4.7 ∘C), and 3.1 ∘C (1.8 to 4.4 ∘C) per doubling of CO2. These values are generally similar to those assessed by the IPCC (1.5 to 4.5 ∘C per doubling CO2) but appear incompatible with low ECS values ( per doubling CO2).

The anticyclonic high-pressure systems over the southern-hemisphere, subtropical oceans have a significant influence on regional climate. Previous studies of how these subtropical anticyclones will change under global warming have focused on austral summer while the winter season has remained largely uninvestigated, together with the extent to which the dominant mechanisms proposed to explain the multi-model-mean changes similarly explain the inter-model spread in projections. This study addresses these gaps by focusing on the mechanisms that drive the spread in projected future changes across the Coupled Model Intercomparison Project Phase 5 and 6 archives during both the summer and winter seasons. The southern hemisphere anticyclones intensify in strength at their center and poleward flank during both seasons in the future projections analyzed. The inter-model spread in projected local diabatic heating changes accounts for a considerable amount of the inter-model spread in the response of the South Pacific anticyclone during both seasons. However, model differences in projected zonal-mean tropospheric static stability changes, which in turn influence baroclinic eddy growth, are most influential in determining the often-strong increases in sea level pressure seen along the poleward flank of all the anticyclones during both seasons. Increased zonal-mean tropospheric static stability over the subtropics is consistent with the poleward shift in Hadley cell edge and zonal-mean sea level pressure increases. The results suggest that differences in the extent of tropical-upper-tropospheric and subtropical-lower-tropospheric warming in the southern hemisphere, via their influence on tropospheric static stability, will largely determine the fate of the anticyclones over the coming century. Electronic supplementary material The online version of this article (10.1007/s00382-020-05290-7) contains supplementary material, which is available to authorized users.

Research objective\ud To determine if Muscle Response Testing (MRT) can be used to distinguish lies from truths using blind test patients.\ud \ud Design\ud A prospective study of diagnostic test accuracy was carried out using MRT to distinguish lies from truth.\ud \ud Methods\ud Twenty practitioners who routinely practised MRT were paired with 20 blind test patients (TPs). TPs were asked to speak simple true and false statements about visual stimuli presented subliminally (at 20 ms). In the subliminal phase, pairs performed 20 MRTs and 20 Intuitive Guesses (IG), consisting of 2 blocks of 10 statements each. In the Supraliminal Phase, the same picture-statement pairs were repeated. The order of stimuli presentation was randomly assigned so that each pair was presented with a unique series of stimuli.\ud \ud Results\ud In the Subliminal Phase, MRT accuracy (as percent correct) was found to be 48.5% (95% CI 42.8–54.2), which was no different from IG accuracy (47.8%; 95% CI 43.2–52.3; p = 0.68) or chance (50.0%; p = 0.59), and no different from MRT accuracy during the supraliminal phase (59.0%; 95% CI 50.4–67.6; p = 0.05). However, supraliminal MRT accuracy was significantly different from chance (p = 0.04), indicating that the pairs could perform MRT proficiently.\ud \ud Conclusion\ud The main reason for finding no effect is suspected to be due to an inadequate subliminal methodology, a process which is quite complex. Other explanations of results include: (1) MRT is not a valid test when the TP is blind, (2) Blinding TPs during MRT will produce ambiguous or unpredictable results, or (3) Nonconscious beliefs cannot be elicited using subliminal stimuli. Future research may wish to focus on exploring these possibilities. More specifically, subsequent studies may wish to use different methods to blind TPs, and establish whether MRT can be used to detect nonconscious processes, a generally held consensus among MRT practitioners.

Ongoing declines in insect populations have led to substantial concern and calls for conservation action. However, even for relatively well-studied groups, like butterflies, information relevant to species-specific status and risk is scattered across field guides, the scientific literature, and agency reports. Consequently, attention and resources have been spent on a miniscule fraction of insect diversity, including a few well-studied butterflies. Here we bring together heterogenous sources of information for 396 butterfly species to provide the first regional assessment of butterflies for the 11 western US states. For 184 species, we use monitoring data to characterize historical and projected trends in population abundance. For another 212 species (for which monitoring data are not available, but other types of information can be collected), we use exposure to climate change, development, geographic range, number of host plants, and other factors to rank species for conservation concern. A phylogenetic signal is apparent, with concentrations of declining and at-risk species in the families Lycaenidae and Hesperiidae. A geographic bias exists in that many species that lack monitoring data occur in more southern states where we expect that impacts of warming and drying trends will be most severe. Legal protection is rare among the taxa with the highest risk values: of the top 100 species, one is listed as threatened under the US Endangered Species Act and one is a candidate for listing. Among the many taxa not currently protected, we highlight a short list of species in decline, includingVanessa annabella,Thorybes mexicanus,Euchloe ausonides, andPholisora catullus. Notably, many of these species have broad geographic ranges, which perhaps highlights a new era of insect conservation in which small or fragmented ranges will not be the only red flags that attract conservation attention.

Oxygen minimum zones (OMZs) play a critical role in global biogeochemical cycling and act as barriers to dispersal for marine organisms. OMZs are currently expanding and intensifying with climate change, however past distributions of OMZs are relatively unknown. Here we present evidence for widespread pelagic OMZs during the Pliocene (5.3-2.6 Ma), the most recent epoch with atmospheric CO2 analogous to modern (~400-450 ppm). The global distribution of OMZ-affiliated planktic foraminifer, Globorotaloides hexagonus, and Earth System and Species Distribution Models show that the Indian Ocean, Eastern Equatorial Pacific, eastern South Pacific, and eastern North Atlantic all supported OMZs in the Pliocene, as today. By contrast, low-oxygen waters were reduced in the North Pacific and expanded in the North Atlantic in the Pliocene. This spatially explicit perspective reveals that a warmer world can support both regionally expanded and contracted OMZs, with intermediate water circulation as a key driver.

Southern Ocean bathymetry constrains the path of the Antarctic Circumpolar Current (ACC), but the bathymetric influence on the coupled ocean-atmosphere system is poorly understood. Here, we investigate this impact by respectively flattening large topographic barriers around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers impact both the barotropic and baroclinic forcing of the ACC, which increases by between 3% and 14% when barriers are removed individually and by 56% when all barriers are removed simultaneously. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea, affecting the deep overturning cell. When the barriers are removed, zonal flattening of the currents leads to SST anomalies upstream and downstream of their locations. These SST anomalies strongly correlate to precipitation in the overlying atmosphere, with correlation coefficients ranging between r=0.92 and r=0.97 in the four experiments. Windspeed anomalies are also positively correlated to SST anomalies in some locations but other forcing factors obscure this correlation in general. The meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on overlying winds. However, bathymetry-induced wind changes are too small to affect the overall wave-3 asymmetry in the Southern Hemisphere Westerlies. Removal of Southern Hemisphere orography is also inconsequential to the wave-3 pattern, suggestion a remote control.

International audience; The evolution of hydroclimate in East Asia during the Pliocene—a potential analog of the future greenhouse climate—remains highly uncertain. Here we reconstruct changes in the hydroclimate of Northern China during this epoch. Our results reveal previously undocumented severe drought conditions that persisted through the early Pliocene with a significantly greater magnitude than suggested by other records. Using a broad hierarchy of climate simulations, we find that reduction in the Pacific meridional sea surface temperature (SST) gradient has particularly strong impacts on precipitation over Northern China, which suggests its key role in maintaining drought conditions during the early Pliocene. The weaker Pacific meridional SST gradient causes the weakening of the East Asian summer monsoon precipitation over this region via a reduction of atmospheric northward moisture transport from the ocean, which enhances aridity inland. Our results highlight the fundamental control of the tropical ocean on the extra-tropical hydrological cycle.

International audience; Abstract. The mid-Pliocene (∼3 Ma) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures, and it is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (due to the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. Note that the dynamic effect plays a more important role than the thermodynamic effect in regional precipitation minus evaporation (PmE) changes (i.e., northward ITCZ shift and wetter northern Indian Ocean). The thermodynamic effect is offset to some extent by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth's energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1∘ northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and, hence, altering mid-Pliocene hydroclimate.

Background: While it is now apparent clinical sequelae (often called Long Covid) may persist after acute Covid-19, their nature, frequency, and aetiology are poorly characterised. This study aims to regularly synthesise evidence on Long Covid characteristics, to inform clinical management, rehabilitation, and interventional studies to improve long term outcomes. \ud \ud Methods: A living systematic review. Medline, CINAHL (EBSCO), Global Health (Ovid), WHO Global Research Database on Covid-19, LitCOVID, and Google Scholar were searched up to 17th March 2021. Published studies including at least 100 people with confirmed or clinically suspected Covid-19 at 12 weeks or more post-onset were included. Results were analysed using descriptive statistics and meta-analyses to estimate prevalence with 95% confidence intervals (CIs). \ud \ud Results: Thirty-nine studies were included: 32 cohort, six cross-sectional, and one case-control. Most showed high or moderate risk of bias. None were set in low-income countries, limited studies included children. Studies reported on 10,951 people (48% female) in 12 countries. Most followed-up post hospital discharge (78%, 8520/10951). The longest mean follow-up was 221.7 (SD: 10.9) days post Covid-19 onset. An extensive range of symptoms with wide prevalence was reported, most commonly weakness (41%; 95% CI 25% to 59%), malaise (33%; 95% CI 15% to 57%), fatigue (31%; 95% CI 24% to 39%), concentration impairment (26%; 95% CI 21% to 32%), and breathlessness (25%; 95% CI 18% to 34%). Other frequent symptoms included musculoskeletal, neurological, and psychological. 37% (95% CI 18% to 60%) of people reported reduced quality of life.\ud \ud Conclusion: Long Covid is a complex condition with heterogeneous symptoms. The nature of the studies precludes a precise case definition or evaluation of risk factors. There is an urgent need for prospective, robust, standardised controlled studies into aetiology, risk factors, and biomarkers to characterise Long Covid in different at-risk populations and settings.\ud \ud Systematic review registration: The protocol was prospectively registered on the PROSPERO database (CRD42020211131).

BackgroundWhile it is now apparent clinical sequelae (long COVID) may persist after acute COVID-19, their nature, frequency and aetiology are poorly characterised. This study aims to regularly synthesise evidence on long COVID characteristics, to help inform clinical management, rehabilitation strategies and interventional studies to improve long-term outcomes.MethodsA living systematic review. Medline, CINAHL (EBSCO), Global Health (Ovid), WHO Global Research on COVID-19 database, LitCovid and Google Scholar were searched till 17 March 2021. Studies including at least 100 people with confirmed or clinically suspected COVID-19 at 12 weeks or more post onset were included. Risk of bias was assessed using the tool produced by Hoy et al. Results were analysed using descriptive statistics and meta-analyses to estimate prevalence.ResultsA total of 39 studies were included: 32 cohort, 6 cross-sectional and 1 case–control. Most showed high or moderate risk of bias. None were set in low-income countries and few included children. Studies reported on 10 951 people (48% female) in 12 countries. Most included previously hospitalised people (78%, 8520/10 951). The longest mean follow-up time was 221.7 (SD: 10.9) days post COVID-19 onset. Over 60 physical and psychological signs and symptoms with wide prevalence were reported, most commonly weakness (41%; 95% CI 25% to 59%), general malaise (33%; 95% CI 15% to 57%), fatigue (31%; 95% CI 24% to 39%), concentration impairment (26%; 95% CI 21% to 32%) and breathlessness (25%; 95% CI 18% to 34%). 37% (95% CI 18% to 60%) of patients reported reduced quality of life; 26% (10/39) of studies presented evidence of reduced pulmonary function.ConclusionLong COVID is a complex condition with prolonged heterogeneous symptoms. The nature of studies precludes a precise case definition or risk evaluation. There is an urgent need for prospective, robust, standardised, controlled studies into aetiology, risk factors and biomarkers to characterise long COVID in different at-risk populations and settings.PROSPERO registration numberCRD42020211131.

A pronounced tropical cooling (> 4 °C) and high-latitude warming in the annual mean sea surface temperature (SST) climatology is found in a numerical experiment conducted with a coupled model consisting of an atmospheric general circulation model (AGCM) coupled to a slab ocean model (SOM) in which the time-independent SOM thickness is reduced by a factor of two. The results suggest that biases in the ocean mixed layer depth could be contributing to SST biases in coupled atmosphere–ocean general circulation models. These changes in annual mean SST are noteworthy since in simple climate models the SOM thickness controls the amplitude and phase of the SST annual cycle, but it plays no role in determining the annual mean SST. Results from the numerical experiment indicate that halving of the SOM thickness not only changes annual cycle amplitude but results in asymmetrical changes in the annual cycle that rectify onto annual mean SST. The changed SOM thickness is found to primarily affect the surface net solar flux and latent heat flux components. However, due to the SOM equilibrium energy budget constraint, the annual mean net surface heat flux does not change, and the solar and latent heat fluxes changes compensate for each other. There is no such constraint on the annual cycle of heat fluxes, where the solar and latent components act to reinforce each other over much of the ocean, with the notable exception of the tropic Pacific warm pool region. We investigate the influence of the amplitude of the SST annual cycle on the annual mean SST through the net surface heat flux and its components using a two-step approach. First, two prescribed SST AGCM simulations are carried out, both with the annual mean SST of the full-thickness SOM coupled model simulation: one forced with the SST annual cycle of the full-thickness SOM coupled simulation, and the other forced with the SST annual cycle of the half-thickness SOM coupled simulation. Second, the impacts of these changes in the annual cycle on the annual mean SST are assessed in a full-thickness AGCM-SOM coupled simulation forced by the net, annual-mean, surface heat flux changes produced by the SST annual cycle changes in the first step. It is found that these net surface heat flux changes can largely reproduce the annual mean SST sensitivity to SOM thickness found in the coupled SOM thickness halving experiment. The effects on the annual mean heat flux components and annual mean SST from changes in the SOM thickness in an idealized limiting case are also considered.

California experienced record-setting drought from 2012 to 2017. Based on both seasonal forecast models and historical associations, there was widespread expectation that the major El Niño event of 2015/16 would result in increased winter-season precipitation and break the drought. However, the 2015/16 winter rainy season ultimately resulted in slightly below-average precipitation and the drought continued. In this work we analyze data from both observations and seasonal forecasts made as part of the North American Multi-Model Ensemble (NMME) to better understand the general relationship between El Niño and U.S. West Coast rainfall, focusing on Southern California (SOCAL) rainfall, Pacific Northwest (PNW) rainfall, and the 2015/16 event. We find that while there is a statistically significant positive correlation between El Niño events and the SOCAL and PNW rainfall anomalies, this relationship explains at most one-third of the observed variance. Examination of hindcasts from the NMME demonstrates that the models are capable of accurately reproducing this observed correlation between tropical Pacific sea surface temperatures and California rainfall when information from the individual ensemble members is retained. However, focusing on the multimodel ensemble mean, which deliberately reduces the influence of unpredicted variability, drastically overestimates the strength of this relationship. Our analysis demonstrates that much of the winter rainfall variability along the U.S. West Coast is dominated by unpredicted variations in the 200-hPa height field and that this same unpredicted variability was largely responsible for the unexpectedly dry conditions in 2015/16.

Variability in the strength of low-cloud feedbacks across climate models is the primary contributor to the spread in their estimates of equilibrium climate sensitivity (ECS). This raises the question: What are the regional implications for key features of tropical climate of globally weak versus strong low-cloud feedbacks in response to greenhouse gas–induced warming? To address this question and formalize our understanding of cloud controls on tropical climate, we perform a suite of idealized fully coupled and slab-ocean climate simulations across which we systematically scale the strength of the low-cloud-cover feedback under abrupt 2 × CO2 forcing within a single model, thereby isolating the impact of low-cloud feedback strength. The feedback strength is varied by modifying the stratus cloud fraction so that it is a function of not only local conditions but also global temperature in a series of abrupt 2 × CO2 sensitivity experiments. The unperturbed decrease in low cloud cover (LCC) under 2 × CO2 is greatest in the mid- and high-latitude oceans, and the subtropical eastern Pacific and Atlantic, a pattern that is magnified as the feedback strength is scaled. Consequently, sea surface temperature (SST) increases more in these regions as well as the Pacific cold tongue. As the strength of the low-cloud feedback increases this results in not only increased ECS, but also an enhanced reduction of the large-scale zonal and meridional SST gradients (structural climate sensitivity), with implications for the atmospheric Hadley and Walker circulations, as well as the hydrological cycle. The relevance of our results to simulating past warm climate is also discussed.

Although the majority of people with Covid-19 will experience mild to moderate symptoms and will recover fully, there is now increasing evidence that a significant proportion will experience persistent symptoms for months after the acute phase of the illness. These symptoms include, among others, fatigue, problems breathing, lack of smell and taste, headaches, and depression and anxiety. It is also clear the virus has lasting fluctuating multiorgan sequelae, including affecting not only the respiratory system but also the heart, liver, and nervous system. We present a protocol for a living systematic review that aims to synthesize the evidence on the prevalence and characteristics of post-acute COVID-19. The living systematic review will be updated regularly, approximately every 6 months, as new evidence emerges. We will include studies that follow up at least 100 people with Covid-19 at 12 or more weeks post Covid-19 onset, with no restrictions regarding country, setting, or language. We will use descriptive statistics and, for outcomes reported in two or more studies, we will use meta-analyses to estimate prevalence with 95% confidence intervals (CIs) using the exact method. Heterogeneity between estimates will be assessed using the I2 statistic. Our findings will also be presented as infographics to facilitate transcription to lay audiences. Ultimately, we aim to support the work of policy makers, practitioners, and patients when planning rehabilitation for those recovering from Covid-19. The protocol has been registered with PROSPERO ( CRD42020211131, 25/09/2020).

The mid-Pliocene (~ 3 million years ago) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures and is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. The thermodynamic effect is to some extent offset by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth’s energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1° northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and hence altering mid-Pliocene hydroclimate cycling.

International audience; The tropical Pacific response to radiative forcing remains uncertain as projected future changes to the Walker circulation and SST patterns vary substantially among climate models. Here, we study what sets the magnitude and timescales of the response and why they differ across models. Specifically, we compare the fast and slow responses of the tropical Pacific to abrupt CO2 increases (2, 4, 8, 16 × CO2) in two configurations of the same model family (CESM) that differ in horizontal resolution and mean biases. We find that the model with a higher resolution shows a transient ocean thermostat-like response to CO2-forcing, with a stronger Walker cell and lack of warming in the eastern Pacific trade wind belts. This fast response lasts for about 50 years and is followed by a slight Walker cell weakening and equatorial warming. The second model, with a coarser resolution, shows a weak and short-lasting ocean thermostat response, followed by pronounced Walker cell weakening and eastern equatorial Pacific warming, similar to the long-term pattern noted in previous studies. These fast and slow responses also manifest in experiments where CO2 is gradually increased. We relate the magnitude of the fast ocean-thermostat response to the structure of the equatorial thermocline, setting the strength of the Bjerknes feedback. The magnitude and timing of the delayed eastern equatorial Pacific warming are related to the competition of positive feedbacks amplifying the ocean thermostat against the effect of ocean subsurface warming eroding the thermostat. The latter effect is further amplified by the slowdown of oceanic subtropical cells and enhanced extra-tropical warming. Different balances between these effects could explain the large spread in the model future projections for the tropical Pacific.

International audience; In contrast to the modern-day climate, North Pacific deep water formation and a Pacific meridional overturning circulation (PMOC) may have been active during past climate conditions, in particular during the Pliocene epoch (some 3–5 million years ago). Here, we use a climate model simulation with a robust PMOC cell to investigate the pathways of the North Pacific deep water from subduction to upwelling, as revealed by Lagrangian particle trajectories. We find that similar to the present-day Atlantic Meridional Overturning Circulation (AMOC), most subducted North Pacific deep water upwells in the Southern Ocean. However, roughly 15% upwells in the tropical Indo-Pacific Oceans instead—a key feature distinguishing the PMOC from the AMOC. The connection to the Indian Ocean is relatively fast, at about 250 years. The connection to the tropical Pacific is slower (∼800 years) as water first travels to the subtropical South Pacific then gradually upwells through the thermocline.

Interannual sea surface temperature (SST) variations in the tropical Atlantic Ocean lead to anomalous atmospheric circulation and precipitation patterns with important ecological and socioeconomic consequences for the semiarid regions of sub-Saharan Africa and northeast Brazil. This interannual SST variability is characterized by three modes: an Atlantic meridional mode featuring an anomalous cross-equatorial SST gradient that peaks in boreal spring; an Atlantic zonal mode (Atlantic Niño mode) with SST anomalies in the eastern equatorial Atlantic cold tongue region that peaks in boreal summer; and a second zonal mode of variability with eastern equatorial SST anomalies peaking in boreal winter. Here we investigate the extent to which there is any seasonality in the relationship between equatorial warm water recharge and the development of eastern equatorial Atlantic SST anomalies. Seasonally stratified cross-correlation analysis between eastern equatorial Atlantic SST anomalies and equatorial heat content anomalies (evaluated using warm water volume and sea surface height) indicate that while equatorial heat content changes do occasionally play a role in the development of boreal summer Atlantic zonal mode events, they contribute more consistently to Atlantic Niño II, boreal winter events. Event and composite analysis of ocean adjustment with a shallow water model suggest that the warm water volume anomalies originate mainly from the off-equatorial northwestern Atlantic, in agreement with previous studies linking them to anomalous wind stress curl associated with the Atlantic meridional mode.

Southern hemisphere subtropical anticyclones are projected to change in a warmer climate during both austral summer and winter. A recent study of CMIP 5 & 6 projections found a combination of local diabatic heating changes and static-stability-induced changes in baroclinic eddy growth as the dominant drivers. Yet the underlying mechanisms forcing these changes still remain uninvestigated. This study aims to enhance our mechanistic understanding of what drives these Southern Hemisphere anticyclones changes during both seasons. Using an AGCM, we decompose the response to CO2-induced warming into two components: (1) the fast atmospheric response to direct CO2 radiative forcing, and (2) the slow atmospheric response due to indirect sea surface temperature warming. Additionally, we isolate the influence of tropical diabatic heating with AGCM added heating experiments. As a complement to our numerical AGCM experiments, we analyze the Atmospheric and Cloud Feedback Model Intercomparison Project experiments. Results from sensitivity experiments show that slow subtropical sea surface temperature warming primarily forces the projected changes in subtropical anticyclones through baroclinicity change. Fast CO2 atmospheric radiative forcing on the other hand plays a secondary role, with the exception of the South Atlantic subtropical anticyclone in austral winter, where it opposes the forcing by sea surface temperature changes resulting in a muted net response. Lastly, we find that tropical diabatic heating changes only significantly influence Southern Hemisphere subtropical anticyclone changes through tropospheric wind shear changes during austral winter.