We seek to model the coupled evolution of a planet and a civilization through the era when energy harvesting by the civilization drives the planet into new and adverse climate states. In this way we ask if “anthropocenes” of the kind humanity is experiencing might be a generic feature of planet-civilization evolution. In this study we focus on the effects of energy harvesting via combustion and vary the planet’s initial chemistry and orbital radius.

Both magmatic and tectonic processes contribute to the formation of volcanic continental margins. Such margins are thought to undergo extension across a narrow zone of lithospheric thinning (~100 km). New observations based on existing and reprocessed data from the Eastern North American Margin contradict this hypothesis. With ~64,000 km of 2D seismic data tied to 40 wells combined with published refraction, deep reflection, receiver function and onshore drilling efforts, we quantified along-strike variations in the distribution of rift structures, magmatism, crustal thickness, and early post-rift sedimentation under the shelf of Baltimore Canyon trough (BCT), Long Island Platform and Georges Bank Basin (GBB). Results indicate that BCT is narrow (80-120 km) with a sharp basement hinge and few rift basins. The Seaward Dipping Reflectors (SDR) there extend ~50 km seaward of the hinge line. In contrast, the GBB is 30 wide (~200 km), has many syn-rift structures, and the SDR there extend ~ 200 km seaward of the hinge line. Early post-rift depocenters at the GBB coincide with thinner crust suggesting “uniform” thinning of the entire lithosphere. Models for the formation of volcanic margins do not explain the wide structure of the GBB. We argue that crustal thinning of the BCT was closely associated with late-syn rift magmatism whereas the broad thinning of the GBB segment predated magmatism. Correlation of these variations to crustal terranes of different compositions suggests that the inherited rheology determined the pre-magmatic response of the lithosphere to extension.

Waves generated by tropical cyclones can have devastating effects on coastal regions. However, the role of ocean currents in modifying wave amplitudes, wavelengths, and directions is commonly overlooked in wave forecasts, despite the fact that these interactions can lead to extreme wave conditions. Here, we use satellite observations and wave modeling to quantify the effects of ocean currents on the surface waves generated during a tropical cyclone event in the Arabian Sea. As a case study, this paper documents beams of wave heights originating from the eyewall of a tropical cyclone caused by current-induced refraction. Alternating regions of high and low wave heights in the model simulations are consistent with observations and extend for thousands of kilometers all the way to 100 m isobath. Our results highlight the importance of accounting for wave refraction by currents in order to accurately predict the impact of tropical cyclone generated waves on coastal regions.

Explosive volcanism imposes impulse-like radiative forcing on the climate system, providing a natural experiment to study the climate response to perturbation. Previous studies have identified disagreements between paleoclimate reconstructions and climate model simulations (GCMs) with respect to the magnitude and recovery from volcanic cooling, questioning the fidelity of GCMs, reconstructions, or both. Using the paleoenvironmental data assimilation framework of the Last Millennium Reanalysis, this study investigates the causes of the disagreements, using both real and simulated data. We demonstrate that discrepancies since 1600 CE can be largely resolved by assimilating tree-ring density records only, targeting growing-season temperature instead of annual temperature, and performing the comparison at proxy locales. Simulations of eruptions earlier in the last millennium may also reflect uncertainties in forcing and modeled aerosol microphysics.

Coastal climate adaptation public works, such as storm surge barriers and levees, are central elements of many strategies to limit damages from coastal storms and sea-level rise. Academic analysis of such public works projects is dominated by technocratic and engineering-driven frameworks. However, social conflict and politics have been crucial in the conception, design, and implementation of other public infrastructure and natural hazard preparedness projects. In this review, we highlight the role of interest mobilization, political motivations, siting opposition, and flexible/adaptive decision-making in both creating and overcoming political obstacles. Better understanding the social and political factors that enable or hinder the implementation of adaptation works could encourage strategies and policies that are less likely to result in deadlocks, delays, or failure, thus saving valuable time and planning resources.

In deglaciating environments, rock mass weakening and potential formation of rock slope instabilities is driven by long-term and seasonal changes in thermal- and hydraulic boundary conditions, combined with unloading due to ice melting. However, in-situ observations are rare. In this study, we present new monitoring data from three highly instrumented boreholes, and numerical simulations to investigate rock slope temperature evolution and micrometer-scale deformation during deglaciation. Our results show that the subsurface temperatures are adjusting to a new, warmer surface temperature following ice retreat. Heat conduction is identified as the dominant heat transfer process at sites with intact rock. Observed non-conductive processes are related to groundwater exchange with cold subglacial water, snowmelt infiltration, or creek water infiltration. Our strain data shows that annual surface temperature cycles cause thermoelastic deformation that dominate the strain signals in the shallow thermally active layer at our stable rock slope locations. At deeper sensors, reversible strain signals correlating with pore pressure fluctuations dominate. Irreversible deformation, which we relate with progressive rock mass damage, occurs as short-term (hours to weeks) strain events and as slower, continuous strain trends. The majority of the short-term irreversible strain events coincides with precipitation events or pore pressure changes. Longer-term trends in the strain time series and a minority of short-term strain events cannot directly be related to any of the investigated drivers. We propose that the observed increased damage accumulation close to the glacier margin can significantly contribute to the long-term formation of paraglacial rock slope instabilities during multiple glacial cycles.

We investigate the steady dynamical response of the atmosphere on the equatorial β-plane to a steady, localized, mid-tropospheric heating source at the equator. Expanding Gill (1980)’s seminal work, we vary the latitudinal and longitudinal scales of the diabatic heating pattern while keeping its total amount fixed. We focus on characteristics of the response which would be particularly important if the circulation interacted with the hydrologic and energy cycles: the overturning circulation and the low-level wind. In the limit of very small scale in either the longitudinal or latitudinal direction, the vertical energy transport balances the diabatic heating and this sets the intensity of the overturning circulation. In this limit, a fast low-level westerly jet is located around the center of diabatic heating. With increasing longitudinal or latitudinal scale of the diabatic heating, the intensity of the overturning circulation decreases and the low-level westerly jet decreases in maximum velocity and spatial extent relative to the spatial extent of this heating. The associated low-level eastward mass transport decreases only with increasing longitudinal scale. These results suggest that moisture-convergence feedbacks will favor small-scale equatorial convective disturbances while surface-heat-flux feedbacks would favor small-scale disturbances in mean westerlies and large-scale disturbances in mean easterlies. Part~II investigates the case of off-equatorial heating.

Since its adoption, the Paris Agreement sets and defines the global climate ambition. The overall scope of this ambition is expressed in its long-term temperature goal in Article 2 as well as the ‘net zero’ mitigation goal in Article 4. To provide guidance to climate policy, the scientific community has explored the characteristics of greenhouse gas (GHG) emission reduction pathways that can meet the Paris Agreement goals. However, when categorizing and presenting such pathways including in reports of the Intergovernmental Panel on Climate Change (IPCC), the focus has been put on the temperature outcome and not on the emission reduction criteria set out in Article 4.1. Here we propose a pathway classification approach that aims to comprehensively reflect all climate criteria set out in the Paris Agreement. We show how such an approach allows for an internally consistent interpretation of the Paris Agreement in terms of emission reduction pathways. For pathways that simultaneously are very likely to hold warming to below 2°C, pursue efforts to limit warming to 1.5°C and achieve the provisions outlined in Article 4.1, we report 2030 global Kyoto-GHG emissions of between 20-26 Gt CO2eq (interquartile range), net zero CO2 emissions around 2050 and net zero GHG emissions around 2060. We further illustrate how prevalent pathway classifications focusing, for example, on the temperature outcome in 2100 result in additional criteria being applied that are not rooted in the Paris Agreement. We outline the consequences of such approaches including for the deployment of carbon dioxide removal (CDR) in such pathways. We find that across pathways classified as ‘no or low overshoot’ pathways in previous IPCC reports, such non-Paris related, additional criteria for end-of-century outcomes may lead to about 20% higher CDR deployment compared to purely achieving the Paris Agreement objectives in mitigation pathways.

Snowmelt-driven floods result in large societal and economic impacts on local communities including infrastructure failures in the U.S. However, the current U.S. government standard design precipitation maps are based on liquid precipitation data (e.g. National Oceanic and Atmospheric Administration’s Precipitation-Frequency Atlas 14; NOAA Atlas 14) with very limited guidance on snowmelt-driven floods. In this study, we developed 25- and 100-year return level design maps of snow water equivalent (SWE) and 1-day and 7-day snowmelt including precipitation events (e.g. rain-on-snow) using long-term observation-based gridded SWE developed by University of Arizona (UA) incorporating the national snow model product (SNOw Data Assimilation System; SNODAS) over the contiguous U.S. (CONUS). For the 44 U.S. states where the NOAA Atlas 14 maps are available, the design snowmelt values from this study exceed the standard design values in 23% of the total extent. The snowmelt values exceed the NOAA Atlas 14 design precipitation by up to 171 and 254 mm in the northeastern U.S.; 127 and 225 mm in the north-central U.S.; and 191 and 425 mm the western mountain U.S. for the 25- and 100-year return levels, respectively. A comparison of 7-day design snowmelt between with and without precipitation shows that including precipitation results in an average increase of 42 mm and 68 mm for 25- and 100-year return levels, respectively, over snowmelt that do not include precipitation. The design snowmelt maps from this study complement the NOAA Atlas 14 design precipitation and provide additional guidance on infrastructure design for snowmelt-driven floods in the CONUS.

Using fully kinetic Particle-In-Cell (PIC) modelling we investigate how magnetic reconnection responds to a varying guide field in one of the inflow regions. We find that the reconnection rate varies significantly when the orientation of the magnetic field changes between being strictly antiparallel and having a guide field. These variations are fairly consistent with the scaling relation for asymmetric reconnection developed by Cassak and Shay (2007). However, the rate is also found to be non-linearly modulated by changes in the ion inflow velocity. The spatio-temporal change in the inflow velocity arises as the magnetic forces reconfigure to regions of different magnetic field strengths. The variations in the inflow magnetic field configuration allow for different gradients in the magnetic field, leading to asymmetries in the magnetic tension force. By momentum conservation, this facilitates asymmetries in the inflow velocity, which in turn affects the flux transport into the reconnection site. The outflow is found to be less laminar when the inflow varies, and various signatures of the inflow variations are identified in the outflow.

The subdued topography of the Turkana Depression separates the elevated Ethiopian and Kenyan Plateaus in East Africa. Mechanisms to explain its topography are debated because constraints on upper mantle structure and dynamics are lacking. Attempts to understand the role of the mantle below Turkana in the evolution of rifting between the Main Ethiopian and Southern East African rifts and the onset of Ethiopian Flood Basalt volcanism are also hindered by limited data availability. Here, recently deployed seismic networks in Turkana and neighboring Uganda enable us to develop a new absolute P-wavespeed tomographic model (AFRP21) to image mantle structure below the Turkana depression. Additionally, we use P-to-s receiver functions to map the mantle transition zone (MTZ) discontinuity structure. In the shallow mantle, broadly distributed slow wavespeeds reside below the Main Ethiopian rift. To the south, slow wavespeeds occur in a focused zone below the East African rift, but beneath the northern Turkana depression these are cross-cut by a narrow E-W band of fast wavespeeds. At upper MTZ depths slow wavespeeds are broadly continuous below the East African rift but begin to separate into two distinct anomalies at the base of the MTZ. While receiver functions reveal a broadly thinned MTZ below Cenozoic rift-related magmatism in East Africa, the thinnest transition zone exists below the Turkana Depression. Slow wavespeeds and a thinned MTZ below the Turkana Depression indicate hot upwelling material, thus its low-lying nature is not due to the lack of underlying dynamic support. Instead, the depressed topography may be better explained by Mesozoic-Cenozoic E-W rifting associated with the imaged shallow fast wavespeed band. Furthermore, the main eruptive phase of Ethiopian Flood basalt volcanism may be associated with the African plate’s position over the anomalously thinned MTZ in Turkana at ~30Ma.

This work documents version two of the Department of Energy’s Energy Exascale Earth System Model (E3SM). E3SM version 2 (E3SMv2) is a significant evolution from its predecessor E3SMv1, resulting in a model that is nearly twice as fast and with a simulated climate that is improved in many metrics. We describe the physical climate model in its lower horizontal resolution configuration consisting of 110 km atmosphere, 165 km land, 0.5° river routing model, and an ocean and sea ice with mesh spacing varying between 60 km in the mid-latitudes and 30 km at the equator and poles. The model performance is evaluated by means of a standard set of Coupled Model Intercomparison Project Phase 6 (CMIP6) Diagnosis, Evaluation, and Characterization of Klima (DECK) simulations augmented with historical simulations as well as simulations to evaluate impacts of different forcing agents. The simulated climate is generally realistic, with notable improvements in clouds and precipitation compared to E3SMv1. E3SMv1 suffered from an excessively high equilibrium climate sensitivity (ECS) of 5.3 K. In E3SMv2, ECS is reduced to 4.0 K which is now within the plausible range based on a recent World Climate Research Programme (WCRP) assessment. However, E3SMv2 significantly underestimates the global mean surface temperature in the second half of the historical record. An analysis of single-forcing simulations indicates that correcting the historical temperature bias would require a substantial reduction in the magnitude of the aerosol-related forcing.

When quadrupling the atmospheric CO$_{2}$ concentration in relation to pre-industrial levels, most global climate models show an initially strong net radiative feedback that significantly reduces the energy imbalance during the first two decades after the quadrupling. Afterwards, the net radiative feedback weakens, needing more surface warming than before to reduce the remaining energy imbalance. Such weakening radiative feedback has its origin in the tropical oceanic stratiform cloud cover, linked to an evolving spatial warming pattern. In the classical linearized energy balance framework, such variation is represented by an additional term in the planetary budget equation. This additional term is usually interpreted as an ad-hoc emulation of the cloud feedback change, leaving unexplained the relationship between this term and the spatial warming pattern. I use a simple non-linearized energy balance framework to justify that there is a physical interpretation of this term: the evolution of the spatial pattern of warming is explained by changes in the ocean’s circulation and energy uptake. Therefore, the global effective thermal capacity of the system also changes, leading to the additional term. In reality, the clouds respond to what occurs in the ocean, changing their radiative effect. In the equation, the term is now a concrete representation of the ocean’s role. Additionally, I derive for the first time an explicit mathematical expression of the net radiative feedback and its temporal evolution in the linearized energy balance framework. This mathematical expression supports the new proposed interpretation. As a corollary, it justifies the twenty-year time scale used to study the variation of the net radiative feedback.

We use a recently developed spectrally resolved bio-optical module to better represent the interaction between the incoming irradiance and the heat fluxes in the upper ocean within the (pre-)operational physical-biogeochemical model on the North-West European (NWE) Shelf. The module attenuates light based on the simulated biogeochemical tracer concentrations, and thus introduces a two-way coupling between the biogeochemistry and physics. We demonstrate that in the late spring-summer the two-way coupled model heats up the upper oceanic layer, shallows the mixed layer depth and influences the mixing in the upper ocean. The increased heating in the upper oceanic layer reduces the convective mixing and improves by ~5 days the timing of the late phytoplankton bloom of the ecosystem model. This improvement is relatively small compared with the existing model bias in bloom timing, but sufficient to have a visible impact on model skill. We show that the changes to the model temperature and salinity introduced by the module have mixed impact on the physical model skill, but the skill can be improved by assimilating the observations of temperature, salinity and chlorophyll concentrations into the model. However, in the situations where we improved the simulation of temperature, either via the bio-optical module, or via assimilation of temperature and salinity, we have shown that we also improved the simulated oxygen concentration as a result of the changes in the simulated air-sea gas flux. Overall, comparing different 1-year experiments showed that the best model skill is achieved with joint physical-biogeochemical assimilation into the two-way coupled model.

We investigate the veracity of the reports by Iwata & Umeno (2016, doi:10.1002/2016JA023036) and Iwata & Umeno (2017, doi:10.1002/2017JA023921), both of which claimed that the observed perturbations in GNSS-based ionospheric total electron content (TEC) could serve as a “precursor” of large earthquakes based on correlation analysis. Iwata & Umeno (2016) defined a spatial correlation of residuals between the observed and predicted TEC time series. They reported that the correlation value is significantly larger before large earthquakes than those observed during non-earthquake periods. Iwata & Umeno (2017), who applied the same method to other large earthquake, claimed that the preseismic ionospheric disturbances can be distinguished from other non-earthquake phenomena based on the small percentage of area where the correlation value exceeds the criterion. They also claimed that the low propagation velocity of the correlation peaks is also a pre-seismic characteristic. Here we tested their claims using a larger dataset. As a result, these three characteristics they claimed to have captured as evidence of earthquake precursors are not significant being frequently observed during normal (non-earthquake) days. In addition to that, the criteria of Iwata & Umeno (2017) cannot be applied to the large earthquake discussed by Iwata & Umeno (2016), and vice versa. Therefore, we can find no basis for claiming that they detected precursors to the earthquakes. The calculation procedure of the correlation function shows that the value is more of an indicator that amplifies small variations synchronized between nearby stations, like medium-scale traveling ionospheric disturbances rather than earthquake precursors.

We spectrally resolve the conventional clear-sky temperature and water vapor feedbacks in an idealized single-column framework, and show that the well-known partial compensation of these feedbacks is actually due to an almost perfect cancellation of the spectral feedbacks at wavenumbers where H2O is optically thick. This cancellation is a natural consequence of ‘Simpson’s Law’, which says that H2O emission temperatures do not change with surface warming if RH is fixed. We provide an explicit formulation and validation of Simpson’s Law, and furthermore show that this spectral cancellation of feedbacks is naturally incorporated in the alternative RH-based framework proposed by Held and Shell (2012) and Ingram (2012, 2013), thus bolstering the case for switching from conventional to RH-based feedbacks. We also find a negligible RH-based clear-sky lapse rate feedback, suggesting that the impact of changing lapse rates depends crucially on whether relative or specific humidity is held fixed

The Polar Cap (PC) indices are derived from the magnetic variations generated by the transpolar convection of magnetospheric plasma and embedded magnetic fields driven by the interaction with the solar wind. The PC indices are potentially very useful for Space Weather monitoring and forecasts and for related research. However, the PC index series in the near-real time and final versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) are considered unreliable. Both versions include solar wind sector (SWS) effects in the calculation of the reference levels from which magnetic disturbances are measured. The SWS effects are caused by current systems in the dayside Cusp region related to the Y-component, B, of the Interplanetary Magnetic Field (IMF). However, the IAGA-endorsed handling of SWS effects may generate unfounded PC index changes of up to 3 mV/m at the nightside away from the Cusp. For the real-time PCN and PCS indices, the cubic spline-based reference level construction may cause additional unjustified index excursions of more than 3 mV/m with respect to the corresponding final index values. Noting that PC index values above 2 mV/m indicate geomagnetic storm conditions, such unjustified contributions are considered to invalidate the IAGA-endorsed PC index series. Alternative derivation methods are shown to provide more consistent index reference levels for both final and real-time PC indices, to reduce their unfounded excursions, and to significantly increase their reliability.

The quantification and monitoring of photosynthesis are essential to understand the global carbon cycle and vegetation’s responses to climate. Among the different remotely-sensed photosynthesis-related variables, Sun-Induced chlorophyll a Fluorescence (SIF) is especially promising since it results directly from photochemical energy conversion but uncertainties still complicate its interpretation. Recent studies have pointed to the influences of vegetation biochemistry and structure on radiative transfer as the main confounding factors for the use of SIF as a photosynthesis proxy. Leaf-level fluorescence research has shown that such influences may be removed by adjusting the raw fluorescence signal to the emitting leaf’s spectra and we suggest that this can be upscaled to the landscape level. In this study we present and test new Spectrally-Adjusted SIF formulations (SASIFs), along with previously proposed SIF modifications and other acknowledged photosynthesis productivity proxies, against carbon-flux data from vegetation of diverse structure. Accordingly, we used Gross Primary Productivity (GPP) data spanning periods from two to seven years, from 27 FLUXNET sites classified into different Land Cover Classes (LCCs) as defined by the International Geosphere-Biosphere Programme (IGBP). The data tested against GPP was calculated with GOME-2 SIF data, MODIS reflectance and spectral vegetation indices, and it included: NIRV, SIF from the red and the far-red frequency peaks, SIF normalized by the cosine of the Sun’s zenith angle, SIF-yield, new SASIFs and FLUXCOM GPP. The relationships between all variables and FLUXNET GPP were tested using time-series decomposition, site- and LCC-specific Kendall’s rank correlation tests and linear mixed model analysis. Results show that one of our new SASIFs has the best overall correlation to FLUXNET GPP among all tested data. Our LCC-specific analysis demonstrates the influences of biochemistry, phenology, temporal resolution and vegetation structure on the relationships between the tested variables. Results support the idea that chlorophyll fluorescence can be complemented with reflectance data improving our ability to monitor vegetation productivity and predict climate-driven changes to standing biomass in spite of their particular limitations.